Fisheries science JSFS , tập 78, số 4, 2012 3

Fish Sci (2012) 78:753–760 DOI 10.1007/s12562-012-0498-0 ORIGINAL ARTICLE Fisheries Fluctuations of abundance and survival rate during the egg and larval stages of Japanese anchovy Engraulis japonicus in the Seto Inland Sea (1980–2007) Naoaki Kono • Hiromu Zenitani Received: February 2011 / Accepted: 28 March 2012 / Published online: 28 April 2012 Ó The Japanese Society of Fisheries Science 2012 Abstract In order to understand the processes affecting early survival of the Japanese anchovy Engraulis japonicus population in the Seto Inland Sea, we examined the monthly fluctuations in the abundance and survival rates from eggs to recruits (15-day-old larvae, 13 mm in standard length fish, defined as 1-month-old fish) during their main spawning season from 1980 to 2007 The abundance of the yolksac larvae positively correlated with the abundance of eggs, but the abundance of recruits did not significantly correlate with the abundance of yolksac larvae These results imply that the survival rate during the egg stage is relatively stable, but that the rate during the larval stage is variable Of the three most recent decades (1980s, 1990s and 2000s), the abundance of recruits was highest in the 1980s The decrease in the abundance of recruits after the 1990s can be considered to have occurred through a decline in survival rate during the larval stage because there were no significant differences in egg abundance, yolksac larval abundance, and survival rates during the egg stage in the three decades of the study period N Kono (&) National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan e-mail: nkono@fra.affrc.go.jp H Zenitani Fisheries Research Institute, Toyama Prefectural Agricultural, Forestry and Fisheries Research Center, 364 Takatsuka, Namerikawa, Toyama 936-8536, Japan e-mail: hiromu.zenitani@pref.toyama.lg.jp Present Address: H Zenitani National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan Keywords Anchovy Á Egg abundance Á Engraulis japonicus Á Larval abundance Á Recruitment Á Survival rate Á The Seto Inland Sea Introduction The Japanese anchovy Engraulis japonicus is distributed from Sakhalin to the Philippines and is a common pelagic fish in the waters surrounding Japan [1] Three stocks of Japanese anchovy are thought to exist, based on fishing and migration patterns: the Pacific stock, the Tsushima Current stock, and the Seto Inland Sea stock [2] The Seto Inland Sea (Fig 1) is a semi-enclosed sea area and is characterized by a high productivity [3] Japanese anchovy is one of the most important commercial fishing species [4] and a key species in the ecosystem, i.e., it is the prey of higher predators [5] In the Seto Inland Sea, it is mostly caught by boat seine and small purse seine, and the catches are categorized in catch statistics as ‘shirasu’ (late-stage larvae: \40 mm in total length, TL) and ‘Katakuchi-iwashi’ (from juveniles to adults: TL of approx C40 mm) After the 1990s, the catches of both categories have been almost the same amount in the Seto Inland Sea (Fig 2), and the economic importance of ‘shirasu’ to anchovy fisheries has been increasing comparatively Japanese anchovy recruit as ‘shirasu’ to the larval anchovy fishery from the size of about 10 mm TL [6] It is important to elucidate the early survival processes from the egg stage to recruitment as ‘shirasu’ to predict the abundance of anchovy recruits However, to identify the survival process, it is essential to determine the fluctuations in abundance at each developmental stage from the egg stage to recruitment In order to understand the early survival processes of the anchovy population in the Seto Inland Sea, we 123 754 Fish Sci (2012) 78:753–760 130°E 150°E 150 Katakuchi-iwashi Shirasu Ja Catch (103 t) 40°N n pa Pacific Ocean 30°N 34°N 100 50 1970 1975 1980 1985 1990 1995 2000 2005 Year 33°N Fig Inter-annual fluctuation in catches of ‘shirasu’ [late-stage larvae of Japanese anchovy: up to about 40 mm in total length (TL), open bars] and ‘Katakuchi-iwashi’ (from juveniles to adults of Japanese anchovy: about C40 mm in TL, closed bars) in the Seto Inland Sea Materials and methods 34°N 33°N 131°E 132°E 133°E 134°E 135°E Fig Maps of the study area showing the Seto Inland Sea The Seto Inland Sea is the sea area enclosed by three solid lines (middle map) Crosses indicate net towing stations in the egg and larval census The Seto Inland Sea was partitioned into six sea areas, shown by the dotted lines, for calculating egg and yolksac larval abundance Open circles indicate fisheries ports where catch and biological data used in virtual population analysis were obtained (bottom map) examined the monthly fluctuations in the abundance and survival rates from eggs to recruits [15-day-old larvae, standard length (SL) of 13 mm, defined as 1-month-old fish] during their main spawning season We first estimated the monthly abundance of eggs and yolksac larvae of Japanese anchovy from 1980 to 2007 in the Seto Inland Sea by egg and larval census As the life span of the Japanese anchovy is only a few years [1], and the duration of the main spawning season is months [7], it is difficult to estimate the practical abundance by virtual population analysis (VPA) based on data of the catch numbers for each year-old fish and in each year Therefore, we used the abundance of anchovy by VPA based on the catch data for each month-old fish and in each month and demonstrated the quantitative relationships among them in the main spawning season 123 Egg and larval census Intensive egg and larval censuses of coastal fishes in the Seto Inland Sea have been carried out every month since 1980 by 13 Prefectural Fisheries Experimental Stations located in 11 prefectures (Ehime, Fukuoka, Hiroshima, Hyogo, Kagawa, Oita, Okayama, Osaka, Tokushima, Wakayama, Yamaguchi) adjacent to the coast in the Seto Inland Sea Data from 1980 to 2007 were analyzed in the study reported here Vertical tows of a conical net with a side length of 80 cm [8] or of a cylindrical conical net with a side length of 65 cm at the cylindrical part and 130 cm at the conical part [9] were used for ichthyoplankton sampling The nets have an inside mouth diameter of 45 cm and a mesh aperture of 0.330 or 0.335 mm The nets were equipped with a flow-meter to standardize the filtering efficiency and the length of the tow path of the net Each net was retrieved vertically at m s-1 from a depth of 50 m or from the bottom at stations shallower than 50 m Tow samples were preserved in 5–10 % seawater formalin, and anchovy eggs and larvae were sorted from these tow samples Sampling stations were organized to cover the entire Seto Inland Sea (Fig 1), and data from a total of 68,571 tow samples, ranging from 1,762 to 2,909 tows per year, were used in this study The sea surface temperature (SST) was measured simultaneously with the net towing at each station Calculation of abundance of eggs and larvae Due to the absence of data for yolksac larvae in some areas, we were unable to calculate the abundance of yolksac 755 larvae for nine of the sampling areas, following Kono and Zenitani [7] Therefore, the survey area in the Seto Inland Sea was divided into six sea areas for convenience in our study, and each tow sample was assigned to one of the sea areas (Fig 1) The egg abundance, Ei,j, standardized by the incubation time in the i-th sea area in month j, was calculated as X  Xi;j;k  Ei;j ¼ Á Dj Á Ai ð1Þ Á ni;j IEi;j;k k where Xi,j,k is the density of eggs in the i-th sea area in month j at the k-th station (number of eggs per m2 of the water column), IEi,j,k is the egg incubation time in days in the i-th sea area in month j at the k-th station, ni,j is the number of stations in the i-th sea area in month j, Dj is the number of days in month j, and Ai is the area in square meters of the i-th sea area The egg incubation time was calculated after Hattori [10] as À Á À Á 483:26 exp À0:121Ti;j;k IEi;j;k ¼ 14 Ti;j;k 26  C 24 ð2Þ where Ti,j,k is the SST in the i-th sea area in month j at the k-th station The egg abundance, Ej, standardized by the incubation time, for month j over the entire survey area was calculated as X Ej ¼ Ei;j : ð3Þ i The yolksac larval abundance, Li,j, standardized by the duration of the yolksac larval stage in the i-th sea area in month j, was calculated by the same procedure as that used for egg abundance as X  Yi;j;k  Li;j ¼ Á D j Á Ai ð4Þ Á ni;j ILi;j;k k where Yi,j,k is the density of yolksac larvae in the i-th sea area in month j at the k-th station (number of yolksac larvae per m2 of the water column), and ILi,j,k is the duration of the yolksac larval stage in days in the i-th sea area in month j at the k-th station The equation for the duration of the yolksac larval stage of Japanese anchovy was constructed using information obtained in previous rearing experiments [11–14] as (Fig 3) 386:83 expðÀ0:085Ti;j;k Þ 24 ðn ¼ 9; r ¼ 0:922; p\0:001Þ: ILi;j;k ¼ ð5Þ Duration of the yolksac larval stage days Fish Sci (2012) 78:753–760 y = (386.83/24) e-0.085 x = 0.922 15 17 19 21 23 25 27 Water temperature Fig Relationship between seawater temperature and duration of the yolksac larval stage of Japanese anchovy under rearing experiments Plots were redrawn from published data Open circles, triangles, squares, and crosses refer to data from Azeta [11], Fukuhara and Takao [12], Imai and Tanaka [13], and Kono et al [14], respectively The yolksac larval abundance, Lj, standardized by the duration of the yolksac larval stage, of month j over the entire survey area was calculated as X Lj ¼ Li;j : ð6Þ i Anchovy recruits Anchovy abundance at each age (month-old) and in each month has already been estimated from January 1981 to December 2007 in the Seto Inland Sea by VPA based on the catch abundances at each age (month-old) and in each month calculated from data of Japanese anchovy sampled at 44 fishing ports (Fig 1) by Kono and Zenitani [15] We used 1-month-old fish (15-day-old larvae, 13-mm SL fish) abundance as recruits, as anchovies are caught from a size of about 10 mm TL in the Seto Inland Sea [6] VPA is a fairly robust procedure for examining historical trends in abundance [16] Survival rates Only the survival rates for the whole Seto Inland Sea could be calculated because the number of recruits were calculated for the whole Seto Inland Sea Japanese anchovy spawn abundantly from June to August in the Seto Inland Sea [7] Therefore, we calculated the survival rates during the egg stage (from eggs to yolksac larvae) using the egg and yolksac larval abundance from June to August The survival rates during the egg stage, Se, were calculated as 123 756 Fish Sci (2012) 78:753–760 where Rj is the abundance of recruits (1-month-old fish) Although the absolute values of these survival rates must be treated with caution because of biases, such as specific extrusion of different developmental stages through the meshes of the plankton net in net sampling or an assumption of the natural mortality rate after recruitment in VPA, the equations presented here allow the historical trends of these survival rates to be described A part of the recruits of the Pacific stock migrate into the Seto Inland Sea from April to June [17] However, even in the Kii Channel, which is located in the eastern part of the Seto Inland Sea and through which recruits could readily migrate from the Pacific Ocean, recruits caught after July have been shown to mainly originate from eggs spawned within the Seto Inland Sea [18] Data from July to September were also used to calculate the survival rates during the larval stage Therefore, the recruits from the Pacific would scarcely affect the survival rates during the larval stage Results Abundances of eggs, yolksac larvae, and recruits Total egg abundance from June to August in each year fluctuated from 136 trillion in 1988 to 948 trillion in 2002 (Fig 4) Total abundance of yolksac larvae from June to August in each year fluctuated from trillion in 1993 to 125 trillion in 1999 Monthly anchovy abundance in number at each age (month-old) has been estimated from 1981 to 2007 [15] Total abundance of recruits from July to September varied between 95 billion in 1998 and 386 billion in 1985 (Fig 4), with peak abundance during the 1980s, the least abundance during the 1990s, and intermediate abundance during the 2000s 150 12 Yolksac larval abundance (10 ) We considered that recruits in a certain month were derived from yolksac larvae in the preceding month because 15-day-old larvae (1-month-old fish) recruit to the fishery Therefore, survival rates were calculated during the larval stage (from yolksac larvae to 1-month-old fish) using the yolksac larval abundance from June to August, and 1-month-old fish abundance was calculated from July to September The survival rates during the larval stage, Sl, were calculated as PSep: Jul: Rj Sl ¼ PAug:  100: ð8Þ Jun: Lj 123 1000 ð7Þ 12 Ej  100: Egg abundance (10 ) Jun: Lj 800 100 600 400 50 200 0 400 300 Jun: Se ¼ PAug: Recruit (10 ) PAug: 200 100 1980 1985 1990 1995 2000 2005 Year Fig Fluctuations in Japanese anchovy in the Seto Inland Sea from 1980 to 2007 Top Fluctuations in total egg abundance (open circles) and total yolksac larval abundance (closed circles) from June to August Bottom Fluctuations in recruits (1-month-old fish) from July to September Relationships among abundance of eggs, yolksac larvae, and recruits The relationship between the total egg abundance and the total yolksac larval abundance from June to August, and the relationship between the total yolksac larval abundance from June to August and the total recruits from July to September were examined The abundance of yolksac larvae positively correlated with egg abundance (Fig 5; n = 28, r2 = 0.473, p \ 0.001) The abundance of recruits, however, did not correlate with the abundance of yolksac larvae (Fig 6) Comparison of the abundance of eggs, yolksac larvae, and recruits over three decades In order to determine the factors affecting the fluctuations in the abundance of eggs, yolksac larvae and recruits during the three decades of the study (1980s, 1990s, 2000s), we Total yolksac larval abundance 12 from June to August (10 ) Fish Sci (2012) 78:753–760 757 multiple comparison, p \ 0.05] The abundance of recruits after the 1990s was significantly less than that during the 1980s 150 L = 0.0894 E - 4.918 r = 0.473 100 Survival rate 50 0 200 400 600 800 1000 Total egg abundance from June to August (1012) Total recruits from July to September (1-month-old fish abundance, 10 ) Fig Relationship between total egg abundance and total yolksac larval abundance from June to August of Japanese anchovy in the Seto Inland Sea from 1980 to 2007 400 300 200 100 0 50 100 Total yolksac larval abundance from June to August (10 12) The survival rates during the egg stage varied between 3.5 % in 1985 and 19.7 % in 1999 (Fig 7) The coefficient of variation (CV) of the survival rates during the egg stage was 0.47 The survival rate during the larval stage varied between 0.1 % in 1999 and 3.3 % in 1985 Of the three decades under study, the highest survival rate during the larval stage occurred during the 1980s, followed by a gradual decrease until the 2000s The CV of the survival rates during the larval stage was 0.88 The average survival rates among the three decades were compared for the egg and larval stages (Table 2) There were no significant differences among the three decades for survival rates at the egg stage; however, there was a significant difference between the 1980s and the 2000s in terms of survival during the larval stage (one-way repeated measures ANOVA followed by Games–Howell pairwise comparison test, p \ 0.05) The survival rate during the larval stage in the 2000s was significantly lower than that in the 1980s, and that in the 1990s (0.7 %) was less than half the survival rate in the 1980s (1.5 %), although the difference was not significant 150 Fig Relationship between total yolksac larval abundance from June to August and total recruits from July to September of Japanese anchovy in the Seto Inland Sea from 1981 to 2007 compared the average abundance of each developmental stage for each decade (Table 1) There were no significant differences among the three decades for the abundance of eggs and yolksac larvae, whereas there were significant differences between the 1980s and 1990s, and between the 1980s and 2000s for the recruits [one-way repeated measures analysis of variance (ANOVA) followed by Scheffe´’s test for Discussion The major finding of our study is that the abundance of the yolksac larvae tended to be determined by the abundance of eggs, but that the abundance of recruits was not determined by the abundance of yolksac larvae The CV of the survival rates during the larval stage was larger than that during the egg stage These results imply that survival rates during the egg stage are relatively stable, while those during the larval stage are variable Therefore, it may be difficult to predict the abundance of anchovy recruits (15day-old larvae, 13-mm SL fish) from only the abundance of Table Comparison of the abundancea of each developmental stage of Japanese anchovy in the Seto Inland Sea for the three decades under study Developmental stage 1980s 1990s 2000s Eggs (1012) 403.4 ± 189.4 a 375.2 ± 196.7 a 533.7 ± 188.6 a 26.4 ± 21.7 a 36.9 ± 34.6 a 38.3 ± 16.1 a 262.6 ± 85.3 a 161.5 ± 71.2 b 167.7 ± 49.6 b Yolksac larvae (1012) Recruits (10 ) Data are presented as the average ± standard deviation of each decade Values followed by a different lower-case letter are significantly different among the three decades within each developmental stage [one-way repeated measures analysis of variance (ANOVA) followed by Scheffe´’s test for multiple comparison, p \ 0.05] a For eggs and yolksac larvae, total abundance from June to August; for recruits: total abundance from July to September 123 758 Fish Sci (2012) 78:753–760 Survival rate (egg to yolksac lavae, 20 15 10 Survival rate (yolksac lavae to recruits, 1980 1985 1990 1995 2000 2005 Year Fig Fluctuations in the survival rates during the egg stage (top) and larval stage (bottom) of Japanese anchovy in the Seto Inland Sea from 1980 to 2007 eggs and yolksac larvae during the main spawning season in the whole Seto Inland Sea Funakoshi [19] concluded that the annual shirasu catch of Japanese anchovy was generally determined by the annual egg abundance from 1975 to 1986 in the Pacific coast of Japan (Enshu-Nada, Ise Bay and Mikawa Bay) because the regression lines between the egg and the larval abundance and between the larval abundance and shirasu catch were significantly positive However, Nakamura and Fujita [20] concluded that the survival rates and transport due to currents are more important factors than egg abundance in determining the monthly shirasu catch of Japanese anchovy from 1961 to 2001 in almost the same sea area as that examined by Funakoshi [19] (western Enshu-Nada and Ise Bay) Nakamura and Fujita [20] based their conclusion on the maximal coefficients of determination being only 29 % in the Ricker curve used to show relationships between the monthly shirasu catch and the egg abundance In our study, the recruits were not always determined solely by the egg abundance as in Nakamura and Fujita [20] In order to be able to predict the abundance of recruits accurately, we need to examine those factors which are likely to cause fluctuations in survival rates during the larval stage in the future During the last three decades, the abundance of recruits in the Seto Inland Sea was highest during the 1980s and significantly less in the 1990s and 2000s We conclude that this decrease in the abundance of recruits after the 1990s mainly occurred through a decline in survival rates during the larval stage because there were no significant differences between the three decades in terms of egg abundance, yolksac larval abundance, and survival rates during the egg stage With respect to the mortality of anchovy during the egg and larval stage, some causes have been reported up to now, such as the lack of available food [21–23], cannibalism by juveniles and adults during the egg or larval stage [24–27], and predation [5, 24, 25, 27–30] As a basic reason for being independent of these causes of mortality, the larval stage examined in the present study (approx weeks) is longer than the duration during the egg stage (1–2 days) [31], and this longer duration during the larval stage will tend to lead to a higher probability of variability in the survival rate during this stage [32] Another reason for variances in the survival rate is that starvation can affect mortality during the larval stage unlike the egg stage After the ‘critical period’ hypothesis proposed by Hjørt [33], a number of key hypotheses were proposed that examined the implications between the available prey abundance and survival in the early larval life [34, 35] Hunter [36] suggested that larvae of northern anchovy Engraulis mordax at the stage just after yolk absorption are more likely to die from starvation than older larvae in view of their metabolic requirements Starvation in field-sampled larvae has been reported in various marine fish species [21–23, 37, 38] The daily survival rate of Japanese anchovy larvae, which were smaller than 15 mm SL, was low when the concentration of small-sized copepod nauplii in Hiuchi-Nada (a part of the central area of the Table Comparison of the survival rates for the three decades during egg and larval stages of Japanese anchovy in the Seto Inland Sea Developmental stage 1980s 1990s 2000s Egg stage (%) 6.2 ± 3.0 a 9.1 ± 4.7 a 7.1 ± 1.0 a Larval stage (%) 1.5 ± 1.1 a 0.7 ± 0.5 a,b 0.5 ± 0.1 b Data are presented as the average ± standard deviation of each decade Values followed by a different lower-case letter are significantly different among the three decades within each developmental stage (one-way repeated measures ANOVA followed by Games–Howell pairwise comparison test for multiple comparison, p \ 0.05) 123 Fish Sci (2012) 78:753–760 Seto Inland Sea) was low [39], and a possible key factor in the regulation of anchovy recruitment levels is the fluctuation in abundance of the copepod assemblage [40] Variation of the abundance of available food, therefore, might be one of the causes leading to the variation in the survival rates during the early larvae Total egg production between May to September in the Seto Inland Sea of Japanese anchovy was positively correlated with the mean SST during the same period, and the mean SSTs after the middle of the 1990s tended to be higher than those in the preceding period [7] Japanese anchovy populations on the Pacific side of Japan increased during warmer periods [41, 42] However, the increase in the mean SST after the middle of the 1990s in the Seto Inland Sea did not lead to an increase in the abundance of recruits In rearing experiments of Japanese anchovy larvae of approximately 20–30 mm SL [43, 44], the survival rates varied among combinations of seawater temperature (13, 17, 21 and 25 °C) and abundance of food (0, 30, 300 and 3,000 Artemia nauplii fish-1 day-1) The survival rates at 17 °C among all water temperature conditions were the highest in all prey conditions; at C17 °C, the survival rates dropped rapidly with increasing water temperatures but the same prey conditions, and the final survival rates at the higher temperatures were lower Because the metabolic rate of larval fish increases under higher seawater temperature conditions [45] and more energy is consumed, the effects of any deficiency of food intake on the survival rate may become increasingly pronounced at higher temperatures In addition, the abundance and the production rates of copepods have been found to decrease with increasing water temperature in the Seto Inland Sea [40, 46] The mean water temperature in the Seto Inland Sea between August and September is frequently [25 °C, occasionally even at the bottom layer [47, 48] It is therefore possible that the decline in the survival rates during the larval stage after the 1990s may be linked to declining food levels due to the high water temperatures Based on an analysis of growth rates using otolith microstructure, Takahashi and Watanabe [44] showed that mortality of Japanese anchovy in the Kuroshio–Oyashio transition region on the Pacific side of Japan was dependent on growth and developmental rates in the metamorphosing stage (late larvae and early juveniles, 26- to 47-mm SL fish) and that this stage determined the abundance at recruitment (1-year-old fish) In our study, we showed the possibility that there is a survival process affecting population fluctuations even during the developmental stage from yolksac larvae to recruits (15-day-old larvae, 13-mm SL fish), which is an earlier developmental stage than that used for Japanese anchovy in the Kuroshio–Oyashio transition region [44] This process might be the first developmental stage in which survival success regulates the 759 fluctuations of the abundance of Japanese anchovy in the Seto Inland Sea Acknowledgments We thank the many researchers, officers, crews, and operators of the 13 Prefectural Fisheries Experimental Stations located on the Seto Inland Sea coast for their kind assistance during the egg and larval census sampling Egg and larval censuses continue to be carried out with the help of the RV ‘Yoshu’ (77 t) of Ehime, ‘Buzen’ (31 t) of Fukuoka, ‘Aki’ (19 t) of Hiroshima, ‘Shin-Hyogo’ (48 t) of Hyogo, ‘Yakuri’ (19 t) of Kagawa, ‘Hoyo’ (75 t) of Oita, ‘Wakaseto’ (19 t) of Okayama, ‘Osaka’ (28 t) of Osaka, ‘Tokushima’ (80 t) of Tokushima, ‘Kinokuni’ (99 t) of Wakayama, and ‘Seto’ (30 t) of Yamaguchi 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Can J Fish Aquat Sci 64:768–776 43 Takahashi M (2001) Growth and development of larval and juvenile Japanese anchovy (Engraulis japonicus) and their implications for recruitment to spawning population (in Japanese) PhD thesis University of Tokyo, Tokyo 44 Takahashi M, Watanabe Y (2004) Growth rate-dependent recruitment of Japanese anchovy Engraulis japonicus in the Kuroshio– Oyashio transitional waters Mar Ecol Prog Ser 266:227–238 45 Houde ED (1989) Comparative growth, mortality, and energetics of marine fish larvae: temperature and implied latitudinal effects Fish Bull US 87:471–495 46 Zenitani H, Kono N, Tsukamoto Y, Masuda R (2009) Effects of temperature, food availability, and body size on daily growth rate of Japanese anchovy Engraulis japonicus larvae in Hiuchi-nada Fish Sci 75:1177–1188 47 Yamamoto M (2003) The long-term variations in water temperature and salinity in Bisan-Seto, the central Seto Inland Sea (in Japanese with English abstract) Bull Jpn Soc Fish Oceanogr 67:163–167 48 Wanishi A (2004) Variations of water temperature during the recent 30 years in the Suo-Nada region off Yamaguchi Prefecture in the western Seto Inland Sea (in Japanese with English abstract) Bull Yamaguchi Prefectural Fish Res Center 2:1–6 Fish Sci (2012) 78:761–773 DOI 10.1007/s12562-012-0508-2 ORIGINAL ARTICLE Fisheries Basin-scale distribution pattern and biomass estimation of Japanese anchovy Engraulis japonicus in the western North Pacific Hiroto Murase • Atsushi Kawabata • Hiroshi Kubota Masayasu Nakagami • Kazuo Amakasu • Koki Abe • Kazushi Miyashita • Yoshioki Oozeki • Received: September 2011 / Accepted: 24 April 2012 / Published online: June 2012 Ó The Japanese Society of Fisheries Science 2012 Abstract The distribution pattern and biomass of the Japanese anchovy Engraulis japonicus in the offshore region of the western North Pacific (north of 35°N and west of 170°E) were studied using a quantitative echosounder This is the first attempt at such a study in this region Data were collected in summer from 2004 to 2007 The biomass was estimated using data collected at 38 kHz Species compositions in the backscatterings from pelagic fish were assigned based on the results of trawl hauls taking account H Murase (&) The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan e-mail: muraseh@affrc.go.jp Present Address: H Murase National Research Institute of Far Seas Fisheries, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan A Kawabata Á H Kubota Á Y Oozeki National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan M Nakagami Hachinohe Station, Tohoku National Fisheries Research Institute, 25-259 Shimo-mekurakubo, Hachinohe, Aomori 031-0841, Japan K Amakasu Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan K Abe National Research Institute of Fisheries Engineering, 7620-7 Hasaki, Kamisu, Ibaraki 314-0408, Japan K Miyashita Field Science Center for the Northern Biosphere, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan of sea surface temperature (SST) Japanese anchovy tended to be high density to the west of 153°E and were distributed in an SST range of 9–24 °C Although the temporal and spatial coverage of the survey differed each year, at least 1.5–3.4 million tons of Japanese anchovy were present in the survey area between 2004 and 2007 To take account of the spatial coverage of the survey each year, the most reliable biomass estimate for this region in the time period was 3.4 million tons (coefficient of variation 0.22) Keywords Abundance Á Acoustic Á Distribution Á Hydroacoustic Á Kuroshio Á Oyashio Á Pelagic fish Á Stock assessment Introduction Old World anchovies, Engraulis spp., are distributed worldwide, mainly in coastal waters [1] Among these, the Japanese anchovy E japonicus is distributed around Japan and adjacent waters The Pacific stock of the Japanese anchovy is distributed on the Pacific coast side of Japan [2] Although this stock tends to inhabit the coastal region, like other Engraulis spp., it is well documented that the distribution range expands offshore to as far as 180° longitude when the stock is abundant [3–9] Japanese anchovy in the offshore region is considered to be transported from the spawning ground on the coastal side of the Kuroshio by the Kuroshio Extension [10, 11] However, it has been reported that Japanese anchovy also spawn offshore [12–14] Therefore, offshore Japanese anchovy are considered to be a mixture of the offspring of inshore and offshore spawners [9, 15] The results of several studies indicate that the biological characteristics of Japanese anchovy distributed in inshore and offshore 123 950 Fish Sci (2012) 78:947–964 Fig Study sites in Mafia Island in the United Republic of Tanzania Mafia Island 390 44’ E Ras Mkumbi TANZANIA, United Republic BN KANGA INDIAN OCEAN JJ KRG BALENI Zanzibar Island KDN INDIAN Dar es Salaam OCEAN Rufiji River / Delta fisheries has traditionally been prawn trawling, but this has not performed since mid-2008 due to a moratorium imposed by the government The artisanal fisheries employ small-sized motorised or nonmotorised fishing vessels with a maximum length of 11 m and gross tonnage of 20 GT, with low capital investment The majority of the fishers employ nonmechanised gear and vessels constructed from locally available materials The fishing activities are performed in inshore areas, mainly in the coral reef, mangrove creeks, and seagrass beds [21, 22] The community of Mafia is closely knit and organised, with a religious system maintained by elders, leading to social structures that are vital in consultation, decision making, and when initiating actions relating to and performing evaluations of resource use and conservation efforts [20, 23, 24] (http://www.pupilvision.com/uppersixth/ coasts3.htm/) However, the overexploitation of resources presents a potential threat to fisheries resources In comparison to the traditional utilisation of resources by a limited number of locals, the local people’s monopoly on fishing rights has been threatened as more and more fishers from the mainland and neighbouring islands extend their searches to fishing grounds in Mafia Mafia Island Marine Park (MIMP) was the first marine park to be designated by the government in Tanzania, in 1995 The aim was to promote sustainable management of marine resources and community participation [24] The MIMP encompasses various habitats A large number of people reside within the park boundary, and up to 50 % of 123 KIRONGWE Ras Kisimani Legend BN: Bweni JJ: Jojo KRG: Kirongwe KDN: Kilindoni KILINDONI 70 52’ S Pemba Island KIEGEANIChole Bay Juani Is Jibondo Is them depend heavily on the exploitation of marine resources for their livelihoods [20, 24] The MIMP controls the extraction of both living and nonliving resources, construction, marine sports, and unauthorised research [20], with some exceptions for controlled resource use by resident villagers Guimaras Guimaras is an island province of the Republic of the Philippines located in the Western Visayas region It lies in the Panay Gulf, southeast of Panay Island (Fig 3) It is separated from Panay Island by Iloilo Strait (1.5 n.m wide) and from Negros Island by Guimaras Strait (6 n.m wide) Guimaras Province includes the islands of Guimaras, Inampulugan, and many small islands, covering approximately 605 km2 The major fishing ground is the Guimaras Strait, which covers 7,120 km2 and is 18 m deep on average Over 60 % of the cities and municipalities in Guimaras Province face the sea The population of the island is about 151,000 persons, with about 28,000 households The province is basically agricultural, including fisheries Its major industries are tourism, fruit processing, coconut processing, fish farming, handicrafts, mining, and lime production Municipals surveyed in this study include Jordan and Nueva Valencia The fisheries resources of Guimaras are exploited by highly diverse gear types, including handlines, gillnets Fish Sci (2012) 78:947–964 951 Fig Study sites in Guimaras Island in the Republic of the Philippines (drift, bottom, and encircling gillnets), seines (purse, beach, and Danish seines), trawls, squid jiggers, and fixed gear such as a fish corral, which is an arrowheadshaped endemic labyrinth In these fisheries, the only large-scale fishing conducted is purse seining, while Danish seine and encircling gillnets are used in middlescale fishing The other fisheries are small in scale, employing small boats In the small pelagic fisheries, purse seines and drift nets are the most important gear in terms of catch volume Results A total of 127 fishers were interviewed in the three islands: 67 fishers from 30 villages in Pohnpei, 31 fishers from villages in Mafia, and 29 fishers from villages in Guimaras (Table 1) These fisheries are multigear, multispecies systems that are typical of many tropical fisheries Fishers in all three islands perform fishing migrations, with the majority of the fishers venturing into fishing grounds beyond those in the vicinity of their residential areas There are variations in the choice of landing site and market The markets are situated along the coasts of the islands or the adjacent mainland and thus serve as landing sites for some fishers Fishery structure and organisation The fishery structure and organisation in the fisheries of Pohnpei, Mafia, and Guimaras were analysed with regards to the types of fisheries operating (subsistence, small-scale commercial) and administration Pohnpei The development and management of the coastal fisheries in Pohnpei encompass all reef and lagoon fisheries as well as the near-shore fisheries for coastal and pelagic species Generally, subsistence fishers make the greatest use of the inshore resources, while many of the small-scale commercial fishers prefer the near-shore, bottom, and pelagic resources Inshore fishing activities involve 80 % of the fishers, with less than 14 % venturing outside the reef The majority of the fishing is performed in waters 35–50 m deep Mafia The Mafia fisheries are mainly conducted under small-scale commercial and subsistence categories Fishing involves small capital investment, and is mainly performed for subsistence purposes The fishing activities are limited to 123 952 Fish Sci (2012) 78:947–964 Table Numbers of fishers interviewed, administrative units, fishers’ villages, and fish landing sites by island considered in the current study Island Unit No of units No of villages No of landing sites No of fishers Pohnpei (FSM) District 30 16 67 Mafia (Tanzania) Ward 4 31 Guimaras (Philippines) Municipal 12 29 100 % of total gear sampled the inshore areas, targeting mainly the coral reef, mangrove creeks, and seagrass bed fisheries In terms of structure and state, the fisheries are associated with a widespread lack of fisheries support services, a lack of capital, and limited alternative sources of livelihood Coupled with the entry of immigrant fishers, the fisheries are experiencing a rapid increase in fishing effort, especially in the inshore areas, as well as low or noncompliance to management regulations, destructive fishing practices, and resource use conflicts Efforts to mitigate these challenges and to alleviate poverty in coastal communities via government support programmes enacted under national policies have shifted gear/vessel ownership, thus changing the structures and resource-use patterns of fisheries Ringnet/Purse seine Driftnets 80 Bottom gillnet 60 Trolling Bottom Longline 40 Traditional traps Handline 20 Spears Pohnpei Mafia Guimaras Fig Categories of fishing gear used in Pohnpei, Mafia, and Guimaras Guimaras There are two main categories of marine fisheries in Guimaras: municipal fisheries, which are limited to the coastal waters, and commercial fisheries, which use large fishing vessels of more than 3.0 GT in deeper offshore waters However, much of the fishing is done inshore on and around coral reefs, in mangrove bays and in estuaries, with the majority of the bays being overfished The offshore distances of the fishing grounds for over 87 % of the fishers are within 11 n.m., and the grounds are 68 m deep on average Limited livelihood alternatives due to the low level of education attained by the majority of coastal fishers, the rapidly growing population that is dependent on fisheries, and the entry of immigrant fishers (especially from Iloilo and Negros) have led to a rapid increase in fishing effort due to the increased number of fishers, as well as low or noncompliance to management regulations and destructive fishing practices Resource-use conflicts are associated with the entry of commercial fishing vessels into the municipal fishing grounds Resource-use patterns The factors used to assess the resource-use patterns were fishing gear and vessels, catch and fishing effort, the ownership of fishing gear and vessels, and landing sites and markets Two categories of fishing gear with about eight 123 gear types were identified in the three islands: (1) traditional types comprising spears, handlines, and traps; (2) modern types comprising bottom long-lines, trolling lines, bottom gillnets, drift nets, small-scale purse seines, and ring nets The purse seines and ring nets are highly labour intensive Whereas drift nets and handlines were found in all three islands, purse seines, ring nets, and traps were recorded only in Mafia, while trolling lines were characteristic of Pohnpei Spears and bottom gillnets were not recorded in Mafia (Fig 4) Similarly, the fishing vessels were either traditional craft, including dugout and outrigger canoes, or modern vessels such as fibre-reinforced plastic (FRP) boats (Fig 5) Note that foot fishers (who accessed the fishing grounds on foot, without a vessel) are included as a fishing vessel category, and they mainly target the intertidal and inshore areas Divers, targeting reef species such as octopus are also included in this category Fishing gear and vessels Fishing gear Most of the fishing gear types used in Pohnpei were not very labour intensive, and was handled by a small number of fishers (Fig 4) The main fishing gear types were handlines, spears, and drift nets The use of spears was widespread, especially in the reef and outer reef slopes Drift nets and bottom gillnets with mesh sizes of about 3–400 were used to target both pelagic and Fish Sci (2012) 78:947–964 953 100 % Fishers Sampled FRP Boat 80 Plank 60 Plywood Partial Monocoque 40 Canoe 20 Foot-fishers Pohnpei Mafia Guimaras Fig Fishing vessels used in Pohnpei, Mafia, and Guimaras by category Foot fisher: fishers that travel to the fishing grounds on foot, by wading, or by swimming Canoe: wooden dugouts or with planks that mostly employ oars for propulsion, but occasionally use sails Plywood partial monocoque: wooden frames over which marine plywood is stretched to form a partial monocoque (or framed marine plywood), with sails/modified inbuilt engines employed for propulsion; the majority have outriggers Plank: wooden boats made from planks (plank-on-frame); these are propelled by sails or outboard engines, and may have outriggers benthopelagic fish species Trolling lines were used to catch tuna species in outer reef waters Generally, the gear types used in Mafia were much more labour intensive than those used in Pohnpei and Guimaras Within the island, five fishing gear types that can be categorised into two groups were used: (1) labour-intensive gear such as ring nets and purse seines and (2) less labourintensive gear such as portable bamboo basket traps locally known as madema, drift nets, bottom long-lines, and handlines, although Mafia’s trap and drift net fishing operations involved up to 17 fishers per vessel Ring nets were recorded only in urban Kilindoni Spears were absent due to regulations against their use in coral reefs Fishing gear types used in Guimaras were dominated by bottom long-lines and bottom gillnets For the bottom longlines, the number of hooks ranged from 120–1,500 per boat Drift nets and handlines accounted for 12 % each, while spears accounted for about % The types of gear used were region specific; handlines and drift nets were mainly used in the rural areas, while bottom long-lines were mainly used by urban fishers Bottom gillnets were distributed throughout the surveyed sites One distinctive characteristic of the Mafia fisheries was a comparatively wide variation of vessel types covering two categories, which were larger than those found in Guimaras In Mafia, wooden boats constructed from planks employing outboard engines or sails for propulsion (categorised as a plank boat in this study) were dominant Most plank boats were 7–11 m long and used in drift net, ring net and purse seine fisheries They were subcategorised into (a) those made from industrially processed planks and employing outboard engines known locally as Boti; (b) small dhow-type planked boats that are mostly propelled by sails known locally as mashua; and (c) outrigger boats made up of either locally or industrially processed planks and propelled by sails locally known as ngalawa 86 % of the purse seines and ring nets were recorded in Kilindoni, indicating that most of the fishing operations target the fishing grounds in the outer reefs Dugout canoes (mtumbwi) employing oars for propulsion accounted for % of the vessels Foot fishers, mainly targeting crab and octopus, were also recorded In Guimaras, three types of fishing vessels that can be categorised into two classes were recorded: (1) canoes with oars; (2) framed marine plywood with outriggers, employing sails for propulsion (classified as plywood partial monocoques); and (3) outrigger wooden boats that are mainly framed marine plywood (plywood partial monocoques) but have been modified to fit 5–15 hp inboard nonmarine engines The length of the vessels ranged from to 11 m Fishing vessels that use outboard engines as a primary mode of propulsion were not recorded Unlike Pohnpei and Mafia, foot fishers were virtually absent Crew size on fishing vessels The analysis of crew size per vessel showed fishers per vessel in Pohnpei, 1–27 in Mafia, and 1–4 in Guimaras (Fig 6) While fishing with a small number of crew members, small-sized fishing gear, and small vessels prevailed in all three islands, operations with more than eight fishers appeared only in Mafia This reflects the presence of Boti vessels, which are used for technologically advanced fisheries, especially ring nets and purse seines This is the most distinctive characteristic of Mafia fisheries Catch and effort Fishing vessels Fishing vessels in Pohnpei were mainly FRP boats, which accounted for 67 % of the fishing vessels (Table 2; Fig 5) The lengths of the FRP boats ranged from to 13 m, with an average of m The boats employed 10–60 hp outboard engines, with the majority having about 40 hp Canoes, mainly dug out of tree trunks, were also in use The lengths of canoes ranged from to m, with an average of about m, and they employed oars as the main mode of propulsion Foot fishers were also recorded In Pohnpei, the average catch rate was about 12 kg/fisherday The average fishing frequency was 13 days/month (Fig 7), although this number increased in high season (Fig 8) Mafia showed the highest average catch rate at 30 kg/fisher-day, which tended to rise in high season The average fishing effort was 17 days/month, with great variations observed among different fishing gear types A small increase in fishing effort during the high season or 123 954 Fish Sci (2012) 78:947–964 Table Types of vessels used in the island fisheries of Pohnpei in the Federated States of Micronesia, Mafia in Tanzania, and Guimaras in the Philippines, and the classification used for the present study Island Fishing craft Total length (m) Structure Primary propulsion Crew size Classification (this study) Pohnpei Canoea 1–6 Wood Oars 1–7 Canoe FRP FRP Mafia Guimaras a b 3–13 Fibre-reinforced plastic Outboard engine 1–8 Mtumbwic 3–5 Dugout Oars/poles/a few sails 1–5 Canoe Ngalawad Plank on frame (local/modern) with outrigger Sail 4–5 Plank Mashuae 10 Plank on frame (modern) Sail/inbuilt engine 4–6 Plank Botif 6–11 Plank on frame (modern) Outboard engine 4–27 Plank Payaog 3–4 Bamboo Oars/poles 2–3 Canoe Canoe oara,h 3–6 Plywood on frame Oars/poles/sail/modified inbuilt enginesi 1–4 Canoe Bancaj 4–11 Plywood on frame with outriggers Sail/modified inbuilt nonmarine enginek 1–4 Plywood partial monocoque Canoe: wooden dugouts or with planks that mostly use oars for propulsion; occasionally use sails b FRP: fiber-reinforced plastic boats c Mtumbwi: wooden dugouts or with planks that mostly use oars for propulsion; occasionally use sails d Ngalawa: wooden plank-based boats with outriggers (planks are either handmade locally or from factories) originating from the Tanzania Spice Islands (Mafia, Pemba, and Zanzibar) e Mashua: plank boats employing sails or inbuilt engines for propulsion f Boti: plank boats employing outboard engines for propulsion g Payao: bamboo craft that are mostly used to aggregate fish for handline fishing h Canoe: wooden dugouts or marine plywood-on-frame boats, generally with oars or modified to use inbuilt nonmarine engines; these are mostly found in Guimaras Island i Nonmarine engines (mostly hp) are used j Banca: wooden plank boats or framed marine plywood boats employing sails or that are modified to use inbuilt nonmarine engines for propulsion; most have outriggers for stabilisation Nonmarine engines ranging from to 15 hp are used Number of Fishers per vessel k 18 Pohnpei 16 14 Mafia 12 Guimaras 10 0 10 12 14 Vessel length (meters) Fig Number of fishers per vessel in Pohnpei, Mafia, and Guimaras minimal changes in the fishing effort between the high and low seasons were observed In Guimaras, the average catch rate was kg/fisher-day, which was the lowest among the three islands This is attributable to the types and the seaworthiness of the vessels, the gear used, and the status of the resources The average fishing effort was 18 days/ month, which increased in high season 123 Fig Seasonal fish catch rates for the fishers in Pohnpei, Mafia, and Guimaras a The boxes represent the middle half (50 %) of the CPUE values, including the upper and lower quartiles and the median b The vertical lines end at the minimum and maximum The duration of the fishing season was the same as for 8–12 months among the three islands Fishers operating for 30 days per month throughout the fishing season were Fish Sci (2012) 78:947–964 955 % of fishers sampled 100 Foot fisher 80 Employers 60 Hired 40 Shared 20 Self Pohnpei Mafia Guimaras Fig 10 Fishing vessel ownership in Pohnpei, Mafia, and Guimaras Fig Seasonal fishing effort (days/month) for the fishers in Pohnpei, Mafia, and Guimaras a The boxes represent the middle half (50 %) of the CPUE values, including the upper and lower quartiles and the median b The vertical lines end at the minimum and maximum % of fishers sampled 100 80 Employer s 60 Hired 40 Shared 20 Self Pohnpei Mafia Guimaras Fig Fishing gear ownership in Pohnpei, Mafia, and Guimaras recorded in all three islands The majority of these fishers were from rural areas, and used simple gear types and small fishing vessels, especially canoes with oars, indicating subsistence resource use This result suggests a high dependency on fisheries for employment and livelihoods in the three islands Ownership of fishing gear and vessels Both gear and vessel ownership were categorised as selfowned, shared, hired, employer-owned, or foot fishers Self-gear ownership was relatively high—over 92 % of the fishers in Pohnpei and Guimaras owned their gear (Fig 9) In Mafia, only 10 % of the fishers owned their gear; the majority of the gear was shared The phenomenon of employer-owned gear was only seen in Mafia fisheries, accounting for 17 % of the Mafia fishers; it was absent in Pohnpei and Guimaras Self-ownership of vessels was high in Guimaras (79 %) and Pohnpei (65 %), but low in Mafia (10 %), which showed high levels of shared-vessel ownership (Fig 10) These ratios were similar to those for fishing gear Employer-owned vessels accounted for 13% of the vessels in Mafia The employers in Mafia (locally known as tajiri, a rich man) were either mainly senior fishers who had successfully retired from fishing to become fish traders in fishing villages and nearby urban areas, or entrepreneurs living in big cities Vessel hiring was mainly recorded in Pohnpei (18 %) and in Mafia (6 %) only in Kilindoni, where fishers with ring nets hire 8–9 m sailed outrigger boats The vessel-owning seagoing fishers in Mafia were mainly subsistence fishers with 2–3 m dugout canoes, who used traditional traps and handlines that were restricted to the km inshore fishing grounds \10 m deep In Mafia, shared gear or a shared vessel is property owned by a group and used by the group members/owners who work together during fishing and share the income from fishing equally among themselves The higher levels of gear and vessel sharing is attributed to low income among the fishers and the high costs of both the fishing gear and vessels In addition, common sharing was related to organisations such as cooperatives or fishers’ self-help groups Membership of CBOs and hence shared ownership was part of the government’s requirement of the fishers if they were to benefit from government support in purchasing better gear/vessels to utilise the relatively offshore resources (thus also easing the pressure on the inshore resources) Basing on the above analysis of gear and vessel ownership, fishers in three islands were classified into group I (foot fishers), group II (casual labour fishers), group III (gear owning fishers), group IV (vessel-gear owning fishers), or group V (employers who own gear and/or vessels but not go out to sea for fishing); see Fig 11 Group V comprises mainly typical employers and/or those who lease their vessels in the fishery The casual labour fishers of group II are heavily dependent on the group V fishers, and their wages per fishing trip are often based on the net revenue from the day’s fishing in Mafia For example, the 123 956 Fish Sci (2012) 78:947–964 daily income distribution for a group of 16 fishers including 14 casual labour fishers and vessel/gear owners in Kilindoni showed that the captain/vessel owner earned over 41 % of the fishing revenue, while the other fishers got only 4.2 % only a few fishers (28 % of those in Kitti and 10 % of those in Madolenihmw) had access to the Kolonia capital market Overall, 94 % of the fishers in Pohnpei accessed either the municipal or urban markets to sell their catch In Mafia, 91 % of fishers sell their catch at the landing sites within the local villages (including Kilindoni, Bweni, Jojo, and Kirongwe), mainly to middlemen who transport the fish to the main fish market in Dar es Salaam, located about 195 km from Mafia The fishers of Kilindoni, however, had access to additional selling options at the fish processing factory and to retailers It was noted that the Mafia fishers had little access to urban markets, with only 25 % of the fishers transporting their catch to the main fish market The fishers benefit less in Mafia, as a larger share of the income from the fisheries goes to middlemen, the majority of whom are from the mainland In Guimaras, the main landing sites and markets varied with areas Landing sites were located along the Jordan and Nueva Valencia coasts, except for Iloilo and Tigbauan outside the study area Generally, the fishers from remote fishing villages utilised the landing sites and markets in the villages About 89 % of the fishers in the remote villages sold their catch at the landing sites to middlemen who transported the catch to the urban markets on the main islands of Panay and Negros On the other hand, fishers from near the urban areas utilised the numerous landing sites available within these areas Some of these fishers target the urban markets, with 90 % occasionally selling their catch at the Iloilo city market Basing on the fishers’ market utilisation, fish markets in the three islands were categorised into: (1) village markets: including middlemen, retailers, and a nearby fish processing factory within a village; (2) municipal/within the district markets: including nearby municipal markets within a district; and (3) urban markets: including the public market and fish vendors/dealers in big cities Fish landing sites and markets Age structure and distribution among fishers In Pohnpei, the landing sites were within the slightly sheltered creeks located all around the island The main fish markets utilised by fishers fell into three categories: (1) village markets; (2) markets within the district; and (3) an urban market located in Kolonia 75 % of the fishers from the districts neighbouring Kolonia sold their catch at the market in Kolonia (Fig 12), either to fish vendors or directly at the public market Smaller islands such as Mwand and Param, which have no markets within the villages, sold all their marketable catch in the Kolonia market Fishers from relatively rural districts of Kitti and Madolenihmw showed wide variations in their marketing, with some fishers targeting all market categories However, In the fisheries in the three islands, variations in the age of entry to the fisheries as well as the fishers’ workforce age were observed (Fig 13) Pohnpei was characterised by younger fishers, with the age distribution being largely skewed towards young fishers, and the mode being in the 21–30 year age class (36 % of fishers were \30 years old) Early entry for young fishers \21 years old was noted The age structures in both Mafia and Guimaras were characterised by middle-aged to old fishers, with a relatively normal distribution of age and the mode occurring in the 31–40 year age class Fishers \21 years old were not recorded in Mafia and Guimaras, and only about 13 and 10 % of the fishers were below 30 years old in Mafia and % of fishers sampled 100 80 Foot fisher 60 Casual labourfishers Employer 40 Gear-fisher Vessel-gear fisher 20 Pohnpei Mafia Guimaras Fig 11 Classification of fishers in Pohnpei, Mafia, and Guimaras, based on gear and vessel ownership and the nature of the fishing operations % of fishers sampled 100 80 Capital 60 Municipal /within the district 40 Village 20 Pohnpei Mafia Guimaras Fig 12 Categories of fish markets utilised by fishers in Pohnpei, Mafia, and Guimaras Village markets: village market, fish dealers, and nearby fish processing factory; municipal markets within the district: nearby municipal markets within the district; capital: capital city markets (including public markets and fish vendors/dealers) 123 Fig 13 Age distributions of fishers in Pohnpei, Mafia, and Guimaras 957 % of fishers sampled Fish Sci (2012) 78:947–964 40 Pohnpei 30 20 10 % of fishers sampled 40 Mafia 30 20 10 % of fishers sampled 40 Guimaras 30 20 10 < 21 21 - 30 31 - 40 41 - 50 51 - 60 61 - 70 > 71 Age (Years) Guimaras, respectively Fishers aged [70 years were not recorded in Mafia Mafia showed the narrowest age range Fisheries resource management and community participation Institutions responsible for fisheries administration The management of fisheries resources in Pohnpei combines both traditional and modern scientific methods to empower local communities The administration of fisheries development and management activities are divested to separate agencies in the FSM, where, through the Fisheries Section, the national government provides support to state agencies involved in coastal fisheries development and management Legally, administration of the fisheries falls under the auspices of the National Fisheries Corporation, a public body established by the FSM Government to develop and promote profitable and long-term commercial fisheries The Conservation Society of Pohnpei works closely with the government and community to assist the state and municipal governments and the local communities in developing the management of fisheries resources In the administration of the fisheries in Mafia, coastal resource management is delegated to the local government authorities (LGAs) in collaboration with the village authorities under the central government’s supervision The LGAs are legally authorised to manage fisheries through the Fisheries Act, 2003 and the Fisheries Regulations, 2009 in Tanzania The administration is set up such that it creates an environment enabling community participation in the management of the coastal fisheries resources and livelihoods improvement through legally empowered Beach Management Units (BMUs) The fisheries management regimes utilise measures regarding the exploitation of fisheries resources by fishers through fishing gear, zoning to reduce resource-use conflicts, and controlling fishing effort through licensing and MPAs such as MIMP 123 958 Fish Sci (2012) 78:947–964 In the administration of the fisheries in Guimaras, the authority for coastal resource management is delegated to the municipal (local) government units (LGUs) and the fisheries and aquatic resource management councils (FARMCs) The central government only retains a supervisory role Community and stakeholder participation in the planning and decision-making process forms part of the institutional system and is achieved largely through the FARMCs, devolution to LGUs, and a participatory decision-making process Fisheries resource management is delegated to municipal authorities through municipal ordinances under the Local Government Code 1991 and the Fisheries Code 1998 Through these codes, the LGUs are given authority and responsibility for the management of their coastal areas out to 15 km offshore Therefore, the local governments are empowered to both enact appropriate ordinances and enforce all fisheries laws, rules, regulations, and ordinances Community participation Fishers participated by voluntary registered membership in fishery-related CBOs in the three islands at levels of 10, 71, and 52 % in Pohnpei, Mafia, and Guimaras, respectively Pohnpei exhibited the lowest involvement in CBOs, with the majority showing no affiliation (Fig 14) Mafia recorded the highest involvement, mainly in fishers’ self-help groups, followed by fisheries cooperatives The absence of conventional conservation/management CBOs is attributable to the compulsory membership of BMUs under a community-government initiative enacted at the village level to steer collaborative fisheries management Most of the existing CBOs were established with support from the government to improve small-scale fishers’ access to better fishing gear and vessels, and to ensure sustainable management of the inshore resources by shifting the fishing effort to the offshore waters However, nonmembership of % Membership for sampled fishers 100 CBOs was common in Kilindoni, with 57 % of the fishers not being affiliated to any forms of CBOs This is attributable to strong ties between employers and casual labour fishers, particularly in the ring-net fisheries that prevail in Kilindoni In Guimaras, community participation was characterised by membership of two types of fishery-related CBOs: (mainly) fisheries cooperatives, which were mostly located near the urban areas, as well as conservation and management groups Correlation between administration and community participation According to the information and analysis above, participation in CBOs, which is common in Mafia followed by Guimaras, but rather uncommon in Pohnpei, clearly correlate with the fisheries administration systems employed in the three islands, where local communities are empowered or responsibility is delegated to local authorities in Mafia and Guimaras Nevertheless, low or poor participation of fishers in resource management is apparent in all three island fisheries, which is further aggravated by the high mobility of the fishers, especially with regard to targeted fishing grounds, landing sites, and markets Discussion Fisheries resource use and management factors influencing the fishers were comparatively analysed to assess the sustainability of the fishers’ communities in these fisheries The factors included fishery structure and organisation, fishing gear and vessel type, catch rate and catch effort, fishing gear and vessel ownership, distances to landing sites and markets, age of entry to the fishery, and membership of CBOs Based on these, we propose a new concept: fishers’ community sustainability This concept provides a framework for understanding the relations among the above factors, so that they can be integrated into management initiatives None 80 Fishery structure and organisation 40 Resource management / conservation Groups for Selfhelp 20 Fisheries cooperatives 60 Pohnpei Mafia Guimaras Fig 14 Types of community-based organisations (CBOs) linked to fishers in Pohnpei, Mafia, and Guimaras 123 Analysis of the structure and organisation of the fisheries in the three islands suggests characteristically small-scale commercial and subsistence fisheries with some degree of management delegation to the local authorities This has been characterised by different scholars as concentrating fishing effort on or near to the shore [25–30] The structures and organisation of small-scale commercial and subsistence fisheries are often influenced by the geographical location, climate, season, and demographic and socioeconomic factors A widespread lack of capital and Fish Sci (2012) 78:947–964 fisheries support services in Mafia makes it difficult for fishers to obtain fishing vessels capable of venturing offshore, which actually augments subsistence; this, in turn, is further associated with low compliance with management regulations and destructive fishing practices Limited opportunities for income-generating activity diversification imply a high dependency on fisheries for livelihood [11] The promotion of income-generating activities improves community interest in resource management, as observed in Mafia, thus influencing the structure and organisation of fisheries The structure and organisation of fisheries are therefore important for establishing sound management systems to sustain the livelihoods of the coastal fishers On the other hand, disparities in the structures and organisations of fisheries are attributable to differences in geographical characteristics, such as the fishing grounds and markets of the three islands Pohnpei Island contains the capital of the FSM, and hence most of the fisheries are organised along municipal and urban structures, which is supported by the small size of the island and the resulting easy access to various fishing grounds, fish landing sites, and markets Unlike Pohnpei and Guimaras, which lies between two urban island cities (though fishers in remote areas have less accessibility to those markets), Mafia is far from the markets in mainland Tanzania The islands’ comparative location relative to its urbanness and distances from urban areas influence the observed trend in landings and the tendency to market to the urban areas, which helps to shape the respective fisheries and the corresponding fishers’ community Fishing gear and vessels The distribution of fishing gear types employed in Pohnpei differs from the spatial variations in the distribution of gear types in Mafia and Guimaras The use of highly efficient/ effective gear types reflects the resource status of a particular area, as highly efficient gear types are needed to catch fish in a poor resource base In Guimaras, the dominance of low-cost gear types such as handlines and spears in rural areas and bottom long-lines with a large number of hooks in areas near urban centres suggest a subsistence fishery and commercialised fishery with declining resources, respectively [31] In Mafia, the dominance of ring nets in the urban Kilindoni suggests the nature and diversity of the markets, the proximity of the fish processing factory, and the readily available fish buyers This is unlike village areas, which are dominated by drift nets and traditional traps, and are highly dependent on the middlemen who collect fish at the villages On the other hand, small pelagic seine nets are generally too costly for individual fishers to own, and are often leased from employers or shared among group members The labour-intensive shared and 959 employer-owned gear types indicate a relatively large-scale fishery; the ring nets and purse seines in the urban Kilindoni area in particular point to large differences in socioeconomic status among fishers While differences in income levels influence the type of a fishing vessel that can be afforded, Pohnpei fisheries included comparatively expensive FRP fishing boats The relative scarcity of motorised vessels in Mafia is related to the dominant use of outboard engines The modification of vessels to include relatively low-cost nonmarine engines in Guimaras in order to overcome cost limitations indicates the influence of innovative skills in expanding access to relatively distant fisheries resources for small-scale coastal fishers The results suggest the effects of integrated support programmes in building capacity, empowering the economically vulnerable fishers, and redistributing the fishing effort Catch rate and catch effort Differences in the catch rate, fishing effort, and duration of the fishing season among Pohnpei, Mafia, and Guimaras are mainly attributable to the geographical locations of the islands and associated factors The status of the resource base and gear types, including highly catch-productive purse seines and ring nets, also influence catch rates In Mafia, the highest average catch rate is attributable to the resource base and the comparatively large-scale/labourintensive fisheries On the other hand, in Guimaras, where fishers rely on waters that are thought to be rather depleted in resources, the lowest average catch rate was only kg/ fisher-day The similar catch rates in low season for the three sites may indicate that the catch is almost equivalent to the minimum or appropriate level for consumption by fishers The increase in the number of operational days in high season in Pohnpei and Guimaras shows a characteristic of commercialisation, as it reflects the ability of markets to absorb a large amount of catch Mafia’s remoteness from limited markets for the catch and the great dependency of its fishers on middlemen contributes to the limited ability of Mafia fishers to convert their catch into monetary value, explaining the relatively constant interseasonal fishing activities This elucidates the vulnerability of small-scale coastal fishers and suggests that marketingrelated empowerment schemes should be implemented in order to improve the fishers’ livelihood for resource and fishers’ sustainability Fishing gear and vessel ownership In this study, Pohnpei and Guimaras showed relatively high levels of self-gear ownership compared to Mafia This is attributed to the presence of fishers operating individually 123 960 using spears and handlines in Pohnpei and bottom longlines in Guimaras In Mafia, labour-intensive fisheries were mainly characterised by shared gear, including more expensive purse seines and ring nets, suggesting that the fisheries are socially cohesive, leading to the availability of ‘‘communal’’ gear types The high vessel ownership rate among fishers in Guimaras was attributed to the more common use of small vessels and the incorporation of nonmarine engines into the smaller boats, which implies that more fishers could afford both gear and vessels (hence the high level of vessel-gear fishers) Although Pohnpei and Mafia exhibited hired and/or employer’s vessel/gear ownership, the mechanisms that allowed fishing without the need to own gear or a vessel differed for the two fisheries The hired gear/vessel ownership in Pohnpei is based on strong relationships among extended-family members, which allow one member to lease a vessel to another based on trust rather than a business contract In Mafia, the hired or employer gear/ vessel ownership is related to the different economic statuses of the leasing/employing parts of the group The presence of employer and casual labour fisher categories in Mafia is due to the unfair distribution of the monetary returns of fisheries, which favours employers and causes the fisheries profits to be siphoned away from the fishers’ community This channelling of the wealth to the rich is reflected in the employer-owned ring-net investment, which is far greater than the investment of other fishers, which explains the comparatively large socioeconomic differences among fishers in Mafia From a management perspective, a multigroup fishery requires a special approach that accounts for fisher categories There will clearly be problems and complexities in the management of a fishery dominated by casual labour fishers working under employers’ contracts, because the latter group not participate directly in the actual fishing activities Challenges pertaining to an individual fisher category are the central issue for management, and the categorisation of fishers is a special requirement in the formulation of resource utilisation policies Therefore, a clear definition and understanding of the structure of the fishery is useful for fisheries management The ownership patterns reflect the type of fishery and its effects on both resources and fishers’ community sustainability In Mafia, the fishers’ long-term experiences of lacking capital and fisheries services have resulted in an extended employer ownership system associated with a high level of casual labour fishers, meaning that even a relatively technological advanced fishery did not benefit local fishers’ communities and was linked to fisheries management problems Government intervention to promote the fishers’ involvement in management brought ownership changes to sharedamong-fishers’ organisations, thus creating the labour- 123 Fish Sci (2012) 78:947–964 intensive fisheries associated with a decline in the employer and casual labour fisher categories The trends in gear and vessel ownership by Mafia fishers suggest that (1) some fishers are still trapped in the pre-intervention experience associated with unprofitable fishing, poor levels of gear/vessel ownership, and prominent employer/casual labour fisher categories especially in Kilindoni with poor affiliation to CBOs, and (2) post-intervention high shared ownership showing the departure from the pre-experiences These findings suggest that continuing with the positive ownership shift has the potential to improve fishers’ livelihoods, fisheries resource management, and community sustainability Distance to landing sites and markets In all of the islands, the major markets were the urban markets, which can accept a lot of catch The year 2000 Pohnpei census report shows that the labour force forms 58 % of the population, with more than 50 % being employed in the formal sector [32], and they have purchasing power They constitute a reliable market in Kolonia, where, because it is close to the fishing villages and accessible marketing services, most of the catch is sold directly by fishers On the other hand, because their capital cities are a fair distance away, many fishers in Mafia and rural Guimaras are unable to transport their catch to the urban markets These fishers are left with no choice but to rely on village markets, or sell to middlemen at landing sites Mafia and rural Guimaras fisheries are thus typical small scale fisheries as characterised by Salas et al [33], where fishers have limited power to influence the fish market, given their small-scale capital commitment and greater dependence on middlemen for marketing These fishers will consequently continue to earn a meagre income from their fishing toils while a greater percentage of the fisheries revenue is externalised This scenario has a profound effect on the fisheries structure and organisation, as well as the distribution of fishing effort—important aspects to consider for fisheries development and management strategies Regarding fisheries management for sustainability, the lack of fish markets and marketing services for fishers to sell their catch directly, coupled to a reliance on middlemen, means that fisheries in Mafia and rural Guimaras have a low profitability There are no remittance returns from these fisheries to enhance livelihood stability [34], thus reinforcing the characteristic subsistence fisheries associated with poverty and high resource dependency Increased dependency on fisheries meant that fishers often found it harder to turn to nonfishing alternatives [11] There is also reduced compliance with management regulations relating to serious implications not only for resource sustainability Fish Sci (2012) 78:947–964 but also for livelihood stability, which reduces the sustainability of fishers’ communities and hence their ability to continually deliver the functional objectives of the fisheries Age of entry to fisheries The age structure of Pohnpei fishers was similar to that of the island’s overall population, except for the 0–15 years age class—the island’s modal class [32] In the cases of Mafia and Guimaras, the fishers’ age structure showed fewer fishers under 21–30 years old, although this class is the islands’ modal class [35] (http://www.census.gov.ph/ data/pressrelease/2002/pr0206tx.html/) This contrasts with the modes for both islands, which fall in the 0–19 year age class These facts indicate that there is generally late entry to the fisheries, regardless of the trends in the island’s population age structures The early entry to fisheries in Pohnpei makes it easier for experienced fishers to pass on fisheries skills and values to novices, whereas the late entry to fisheries in Mafia and Guimaras makes this process much more difficult or unlikely Early entry therefore suggests the potential for continuity in carrying out the functional objectives of the fisheries in the present and in future generations Continuity of these functional objectives is important for mankind in general, as it provides food security, income, and employment when coupled with fisheries management for resource sustainability In Pohnpei, most of the fishing activities were structured along a family basis, as the families are strongly knitted together; the social capital is strong among family members Family-owned fishing vessels and engines offer an opportunity for youths to enter fisheries early, indicating a dependency on fisheries for income generation associated with affordable participation The early entry to fisheries in Pohnpei creates an environment that provides young entrants with technical and economic support In turn, the supported youths acquire experience, follow their experienced seniors, and use the monetary returns from fishery to invest in the industry and support others Fisheries returns thus become remittance income to enhance livelihood stability [34], and when coupled with proper fisheries management, this fishery presents a model case for a sustainable fishers’ community Late entry into the fisheries of Mafia and Guimaras suggest that the youth on those islands generally not rely on fisheries as their main source of income A lack of capital in the fishers’ communities limits youths from joining the industry in Mafia The fisheries on Mafia, which are characterised by shared fishing vessels/gear ownership and strong cohesion among group members, fail to support early entry The lack of capital in the fishers’ community tends to enhance the casual labour fishers’ category, which 961 depend on employment in labour-intensive ring-net fishing The very low daily wages paid to casual labour fishers limit their ability to invest in the fishery and not encourage early entry in the fishery, thus augmenting their dependency Mafia’s case demonstrates a high dependency associated with limited access to the resource due to less affordable participation In Guimaras, the low early entry rate is attributable to the availability of more favourable livelihood opportunities, as youths can easily migrate to nearby urban areas such as Iloilo City to get favourable jobs Fishers, who are hindered by their elderly age and low levels of education, and thus find it difficult to compete for other opportunities, remain dependent on fisheries for their livelihood The ability of pull migration (individual moves triggered by more attractive circumstances elsewhere, often in urban areas) to reduce resource dependency and improve livelihoods [34] further explains the comparatively high fisherries dependency of Mafia fishers The tendency of factors limiting early entry to augment the dependency on fisheries for a livelihood is supported by different scholars [22, 29, 36], who found that fisheries systems in areas with limited livelihood options, marginalised economies, and inadequate social amenities create an open access trend where fisheries become the only option to coastal communities Due to poor technology and limited returns from the fishery, this tendency impedes the expansion of fisheries activities and limits such activities to the inshore areas [25, 37] Fisheries resource management and community participation The observed correlation between the fisheries administration system for coastal fisheries management and community participation through fishery CBOs in the three islands indicates the effectiveness of empowering local communities to enhance their participation in and improve management Systems with the lowest levels of community participation tend to exclude the fishers from the management process and create barriers between the fishers and resource managers, thus augmenting the poor state of management Unlike Pohnpei, the high participation of fishers in CBOs in Mafia followed by Guimaras reflects the legislation that was brought in to empower community institutions such as BMUs in Mafia and FARMCs in Guimaras There has been increased recognition of the importance of the participation of fishers in effective fisheries management This realisation has resulted in the recent implementation of various management policies and programs emphasising the development of new legal, administrative, and institutional arrangements at both the national and community level [38–41] 123 962 Government support for sound management systems that incorporate CBFM initiatives is important for ensuring the involvement of fishers in the resource management process CBOs are the key to the establishment of CBFM systems In Mafia, government intervention to ensure sustainable management of the inshore resources has led to an increase in CBOs, and in turn to a positive vessel/gear ownership shift to shared, livelihood improvement and strengthened cohesion among group members This social capital is important for participatory fisheries management, in contrast to the individual-based operations in Pohnpei In Japan, for example, fisheries management has retained the traditional CBFM approach [42] with enormous success, as almost all of the fishing vessels are owned by individual fishers; a similar scenario in the coastal fisheries expected in Pohnpei, Mafia and Guimaras When CBFM systems are created with area-based fishing rights, reduced competition for resources and fewer resource-use conflicts among fishers are often guaranteed [38, 43, 44] The implementation of fisheries resources management with initiatives from fishers, as well as the management of the associated ecosystems and the introduction of livelihood improvement initiatives that are acceptable to coastal fishing communities provide the key to the sustainability of these resources and fishers While improving resource-use patterns and restructuring the fisheries are important tasks, the inclusion of fisher-related factors such as their sustainability and their integration into fisheries management is also fundamental in the development and management of coastal fisheries Fishers’ community sustainability Regardless of the factors that contribute to it, a lack of young entrants into the fisheries ultimately impedes the ability of the fishers’ community to continually deliver the functional objectives of fisheries In relation to the distinctive fishers’ operations related to age structure and the noted extremes or early entry against the late entry, we propose the concept of ‘‘fishers’ community sustainability’’ In this perspective, a ‘‘fishers’ community’’ refers to a group of people who are connected to one another through a fishery We define ‘‘sustainability’’ in this context as the community’s ability to continuously carry out the functional objectives of the fishery from generation to generation The concept assumes that there is a sufficient operational period before retirement to transfer fisheries skills Specifically, the concept covers the features and practices of the fishery industry that are responsible for contributing to or hindering the fishers’ community sustainability It includes environmental, social, cultural, and economic aspects of how fishers interact over time The age structure patterns observed in the Mafia and Guimaras 123 Fish Sci (2012) 78:947–964 fisheries lead to various effects that are linked to the unsustainability of these fishers’ communities Fisheries in these areas require special management and development strategies that integrate fisher-related factors, in contrast to areas with strong economies, as is evident from the fishers’ age structures in the three islands The fishers’ age structure therefore represents an especially important parameter to consider in the formulation of resource utilisation policies Lessons This study has established indicators of the sustainability of fishers’ communities Based on the results obtained here, the sustainability of fishers’ communities is linked to the following key factors: (a) the age structure of fishers (in particular, the age of entry to the fishery); (b) monetary returns from fishing (obtained through fish markets and marketing); (c) cohesion among the fishers (social capital; achieved through family members and/or among group or organisation members); and (d) the mitigation of subsistence-related dependency on fisheries resources, due to the availability of alternative income-generation options Comparisons of the fisheries on the three islands teach us important lessons The social capital or the attitudes and values that govern interactions among the fishers, as well as the norms and traditions through which community-level decisions are made [11], influence fishers’ community sustainability In Pohnpei, CBOs were not very popular, and the fisheries were basically organised at the family level On the other hand, the fisheries in Mafia and Guimaras were organised along both family and community lines, suggesting that social capital was stronger in these islands than in the Pohnpei fisheries, which appeared to be more urban and socioeconomically advanced Community sustainability of the Pohnpei fisheries was comparatively high, though low technological advancement was apparent Due to favourable geography (i.e short travelling distances), fishers benefit from the markets and marketing services available These fisheries show a good balance between fish consumers (demand) and the fishing activities, as supported by the social capital generated by close family ties However, the ability of this family/individual-based fishery to sustain both fisheries resources and the fishers’ community as demand increases is questionable The absence of social groupings in the Pohnpei fisheries suggests a loosely knit society, which poses risks to open-access fisheries resources There is a need for proper fisheries management and the maintenance of positive fisheries returns through markets and marketing to achieve both resource and fishers’ community sustainability Guimaras provides youths with limited alternative employment opportunities to fishing, and low fishery returns (especially in rural areas) and very low catch rates Fish Sci (2012) 78:947–964 were common on this island All of these observations suggest that its coastal fisheries are at risk Without any intervention to promote resource sustainability and erode subsistence-related fishery dependency, the future of the fisheries in Guimaras in regards to both resource and community sustainability is uncertain Mafia’s labour-intensive fisheries are the most advanced of the three islands regarding fishing gear technology However, before government intervention, they did not contribute to the majority’s livelihood; instead, these fisheries enhanced subsistence and were not supportive of early entry, thus degrading community sustainability These fisheries needed intervention to overcome the factors hindering sustainability Following the government intervention, these fisheries have shown (an ongoing process of) positive shifts in gear and vessel ownership, with an increase in shared gear and vessels along with a decline in the prominence of the employer and labourer fisher categories Shared ownership strengthens the fishers’ community through local fishers’ benefits, increased capital investment, and (over time) the potential to revert ownership back to the fishers and support early entry Continuing this empowerment should suppress the employer and labourer fisher categories, and thus their negative effects However, the problem of long distances of the fishing villages from the market must also be addressed to enable fishers to sell their catch at a proper price to achieve good returns (e.g., through empowerment to access capital markets for direct sales) A high dependency on a fishery indicates that fishing is key to fishers’ community sustainability, and the loss of coastal fisheries means the total destruction of the entire fisheries-dependent community Mitigating subsistencerelated dependency on fisheries resources is essential in fisheries management Fisheries development must also incorporate the various aspects of fishers’ community sustainability Acknowledgments The authors thank Mr Koichi Sakonju and Mr Nobuo Lopez of the Overseas Fishery Corporation Foundation of Japan, the FSM office in Pohnpei, Mr John Komakoma of the Mafia Zone Fisheries Resource Protection, Dr Ricardo Babaran and the late Mr Cornelius Selario of the University of the Philippines Visayas for their assistance in field organisation and in data collection We acknowledge the Research Institute 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[1 2, 15–17] The distribution patterns of eggs and larvae of Japanese anchovy 1 23 770 Fish Sci (2012) 78:761–7 73 Table 6 Estimated biomass of Japanese anchovy in the survey area for each year ni number of 1 n.mile intervals, A0 surveyed area (1 03 n.mile2 ), B0 biomass (106t ), d degree of coverage Year 2004 2005 2006 2007 Surveyed blocks 1, 2, 3, 6, 7 3, 4, 6, 7, 8 1–8 1–8 Rni 4,7 61 3, 4 40 4,6 79 2,8 30 ... 100 100 0.00 CV 0.00 1.41 0.00 1. 43 2.26 1.70 2.44 2.20 3. 46 2.81 2. 63 2. 13 2.00 0 0 0 13 2 0 2 64 0 3 5 0 0 0 0 % 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00 CV 0.00 0.00 0.00 2.45 0.00 1. 73 2.41 0.00 3. 46 2. 83 0.00 0.00 0.00 0 Mackerels 42 35 3, 0 86 532 1 2,8 08 37 3 9,9 59 878 135 31 0 4 0 0 % 0 29 15 1 72 0 41 20 1 0 0 3 0 0.00 CV 0.00 1.41 0.00 2.00 2 .39 1.55 1. 63 2. 13 3.44 2. 83 0.00 2.67 0.00 7 – – – – 9 5 8... ICES J Mar Sci 53: 155–160 Petitgas P, Masse J, Bourriau P, Beillois P, Bergeron JP, Delmas D, Herbland A, Koueta N, Froidefond JM, Santos M (2006) 1 23 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Hydro-plankton characteristics and their relationship with sardine and anchovy distributions on the French shelf of the Bay of Biscay Sci Mar 70:161–172 Scalabrin C, Masse´ J (19 93) Acoustic detection... 6 5 5 3 6 5 6 2 538 634 637 251 836 774 598 411 q 16.86 8 .30 13. 85 0.00 0.42 0. 73 1.51 1.06 Ak 50 81 101 61 141 137 108 1 13 Bk CV (Bk) 0.85 0.44 0.67 0.60 1.40 0 .35 0.00 0.00 0.06 0.89 0.10 0.19 0.16 0.79 0.12 0. 63 d 2 .39 2. 23 2.00 1.02 2. 23 2.09 1.82 1.22 4 5 3 3 4 5 3 5 425 732 34 4 81 232 501 30 7 208 q 2. 13 19.50 5.69 0.16 0.00 0.00 0.67 3. 69 Ak 50 81 101 61 141 137 108 1 13 2007 Nk Rni Bk CV (Bk)... 14.6 15 .3 0.05 23. 2 10 .3 0.21 6.5 7.6 0.20 2 .3 13 13. 3 0.05 14.8 7.1 0 .32 1.9 13. 7 0.07 16.4 10.1 0.07 6.0 14 14.0 0.10 17.6 4.8 0.18 0.5 10.9 0.29 7.8 13. 5 0.12 15.6 15 13. 6 0.06 16.0 13. 2 0.16 14.4 9.7 0.09 5.4 8.9 0.25 4.0 16 13. 4 0.07 15 .3 10.7 0.07 7.4 8.0 0.26 2.8 14 .3 0.05 18.5 17 13. 7 0.09 16.2 7.5 0. 23 2 .3 6 .3 0.15 1.2 10.0 0.08 5.8 18 12.8 0.18 13. 2 – – – 8.8 0.47 3. 8 9.7 0.12 5 .3 19 14.5... when the SST was low, although no consistent change in length frequency was observed along the SST gradient The mean Lt (range 4.8–15 .3 cm) and corresponding w (range 0.5– 23. 2 g) for anchovy are summarized in Table 3 1 23 1 23 % 0 CV % CV Mackerels % CV 9 13 6 7 4 7 7 1 3 1 Year 12 13 14 15 16 17 18 19 20 21 SST (°C) 1 8,9 64 86 1 6,9 61 3 6,5 47 4,9 89 1 2,0 41 5 8,2 61 3, 4 85 2 0,8 20 1 2,9 54 6 73 140 97 100 71 85... 4 12 5 14 4 AR 10.29 11.79 4.78 8.69 3. 91 7.57 3. 56 10.47 4.78 13. 67 3. 99 7.59 Mean of all populations 8.09 HO 0 .33 33 0.4706 0 .39 22 0.4510 0.1765 0.5686 0. 039 2 0.4510 0 .31 37 0.6471 0.2549 0 .37 26 HE 0.5925 0.7266 0.5546 0.7 637 0. 230 1 0.7551 0.0946 0.6405 0.5456 0.8716 0.29 53 0.5518 FIS 0.4450 0 .36 10 0 .30 20 0.4180 0.2420 0.2560 0.5920 0 .30 50 0. 433 0 0.2670 0.1460 0 .34 25 N 40 40 40 40 40 40 40 40 40 40... between each population pair, relative thickness of arrows relative amount of directional gene flow 1 23 782 Fish Sci (2012) 78:775–7 83 Table 4 Results of migration model selection approach Hypothesis Red variant Ln L Full model Green variant AIC Ln L AIC - 1,2 87 2,5 93 - 736 1 ,3 76 n-island model -806 1,6 17 -650 1 ,3 04 Stepping stone model -927 1,8 60 -681 1 ,3 67 - 1,1 35 2,2 81 - 1,1 35 2,2 81 Source-sink Log- likelihood... Yamashita Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Katsurakoi 11 6, Kushiro, Hokkaido 085-080 2, Japan H Kidokoro Japan Sea National Fisheries Research Institute, Fisheries Research Agency, Suido-cho 1-5 939 -2 2, Niigata 951-812 1, Japan Y Sakurai Faculty of Fisheries Sciences, Hokkaido University, 3- 1-1 Minato-cho, Hakodate, Hokkaido 041-861 1, Japan Introduction Most commercially... 0 .30 91 0. 436 4 0.5091 0.4000 0.0727 0 .38 18 0.0909 0.4545 0.1455 0.6000 0. 036 4 0 .31 24 HE 0.6555 0.6779 0.6 038 0.78 13 0.08 83 0.7281 0.2592 0.6698 0.5479 0.8714 0.2018 0.5 532 FIS 0. 535 0 0 .36 40 0.1660 0.4950 0.1850 0.4 830 0.6550 0 .33 00 0. 739 0 0 .32 00 0.8 230 N 50 NA AR 0.4 632 50 50 50 50 50 50 50 50 50 50 50 12 13 8 8 8 10 1 12 6 12 6 11.51 12.61 7.56 7.92 7.55 9.45 1 11.71 5.96 11 .35 5.92 8.41 8. 73 HO 0.5200