Fish Conservation species, parasites, and diseases that threaten local species’ populations To be responsible, aquaculture enterprises should not be sited where natural habitat is affected, their wastewater should be treated, and they should focus on plant-eating species, raised in closed systems to prevent escape Pollutants Pollution is the introduction of substances in quantities that are threatening to living resources and human health and activities Chemical pollution can cause spectacular mass mortalities or cause subtle changes in population composition, impaired sexual development and reproductive success, impaired growth rates, deteriorated seafood quality, tumors and other diseases, and outbreaks of harmful algal blooms such as red tides, Pfiesteria, or normally innocuous algae that overgrow corals or deplete waters of oxygen Chemical pollutants tend to concentrate in surface waters, where larvae and eggs also concentrate Chemicals enter the seas from sewage, industrial outfall, agricultural runoff, ocean dumping, aquaculture, accidental spills, and from the air (acid rain has significantly damaged freshwater fishes in North America and Europe) Major chemical pollutants include insecticides and herbicides, detergents, PCBs, elements such as chlorine and heavy metals, petroleum products (much of the gasoline/oil mixture run through 2-cycle outboard engines exits unburned), mining wastes, fuel ash, radioactive materials, and excessive nutrients from sewage, farm animals, and fertilizers When algal blooms caused by excessive nutrients use up those nutrients and die, their subsequent decomposition can rob the water of oxygen, suffocating marine creatures The surprising fact that fertilizer or other nutrients in excessive amounts can kill aquatic organisms is sometimes called ‘‘the paradox of enrichment.’’ About three-quarters of marine pollution comes from the land, thus the people causing the pollution not feel its effects directly or immediately, and the people feeling it (e.g., fishers) cannot directly affect its origin Spreading from the mouth of the Mississippi River, nutrient runoff from farm land produces a dead zone greater than 20,000 square kilometers in some years, reducing oxygen concentrations to dangerous levels and affecting important shrimp and oyster fisheries Over the long term, this is more a threat to the Gulf than the spectacular Deepwater Horizon oil blowout of 2010 New York City’s harbor gets more than 27 billion gallons of storm-water, which includes raw sewage, every year That is one reason why laws are necessary In the US clean water legislation has helped keep some fisheries economically viable by controlling pollutants Global Atmospheric Change and Fish Conservation Major atmospheric changes, like global warming and rising CO2 levels, have significant implications on marine life Earth’s climate has changed dramatically as ice ages have come and gone, but these changes took many thousands of years, allowing life-forms long periods in which to adapt Humancaused climate change is happening much faster, and some 449 habitats and species will probably not change or move fast enough to survive The burning of fossil fuels has increased atmospheric levels of carbon dioxide, methane, and other heat-trapping gases, and most scientists agree that this is intensifying the greenhouse effect, the warming of Earth’s atmosphere Oceans slow the buildup of greenhouse gases by absorbing about a third of the carbon produced by burning, but substantial climate change is likely over the next few decades The effects of such changes are not straightforward, but planetary warming is melting polar ice caps; causing population declines in icedependent krill, the shrimplike key prey species for Antarctic fishes, marine mammals, penguins, and other seabirds; causing changes in the distribution of many temperate species; and raising sea levels throughout the world This rise is expected to cause some flooding and loss to coastal marshes, mangrove areas, low-lying islands, and their critical associated fishnursery habitats, as well as to some cities Global warming is directly affecting fish abundances and forcing latitudinal migrations of some populations The Atlantic Cod population in the North Sea is moving northwards, while Cod populations in the Celtic and Irish Seas will likely disappear by 2100 Warming is likely to alter ocean currents Such changes may intensify the recurrent El Nin˜o phenomenon Other possible changes include alteration of currents such as the Gulf Stream and Kuroshio Current, and weakening of major upwellings off South America and Africa Such changes would affect the production, distribution, and survival of fishes and other creatures in the world’s oceans, and alter the fish availability among countries Changing sea temperatures will exert major influence on the survival and distribution of the oceanic populations In parts of the California Current, planktonic animals declined 70% over the last 40 years, a decline many scientists think may be linked to global warming Our addiction to fossil fuels is also driving ocean pH to dangerous levels Our oceans absorb 22 million tons of carbon dioxide (CO2) daily, much from industrial processes, which when dissolved in seawater forms carbonic acid in a process called ‘‘ocean acidification.’’ Ocean pH has dropped from a preindustrial value of 8.18 to 8.07 today, and is expected to reach 7.82 by 2100 (Orr et al., 2005) pH is measured on a logarithmic scale, so a 0.1 decrease means our oceans are 30% more acidic today than 250 years ago This is having a dramatic and wide ranging impact on fish populations and marine ecosystems For some fish species, increasing acidity decreases larval survival and replenishment of reef fishes, interferes with their olfactory system so they not flee predators, and reduces growth Ocean acidification is reducing survival and growth of organisms low on the food chain, with potentially severe ripple-effects through the entire food web Some ecosystems may simply dissolve Coral reefs, made from the calcium carbonate (CaCO3) skeletons of corals and coralline algae, require waters super-saturated in aragonite (one form of CaCO3) to exist and grow While more than 98% of coral reefs were bathed in aragonite-saturated waters before the industrial revolution, ocean acidification has already put 40% of reefs into unfavorable conditions (Cao and Caldeira, 2008) If CO2 levels increase as predicted, by 2050 aragonite levels will be too low to support the formation of coral reefs