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A Reorganization of the Seas
by Marisa Baxbaum
Evidence is mounting that our seafood preferences are causing a vast shift in the composition of aquatic ecosystems. Unless the developed world can curb its appetite for big fish – species such as tuna, cod, swordfish, marlin, grouper, haddock, sharks, and skate – these creatures will soon exist only in biology textbooks and Hemingway novels.
Threatened by overfishing. Illustration by Richard Ellis ram.biology.dal.ca
Globally, fish comprises 12% of our per capita calorie intake. In 2006, 76 million tons of commercial seafood – or seven trillion individual fish – were caught and consumed. Industrial fishing practices have become so effective that numbers of predator fish, like the ones pictured above, are dwindling. Using historical data on catch rates from 1880 to 2007, scientists at the University of British Columbia found that populations of predatory fish across the globe have declined by two thirds in the past 100 years – with 54% of that decline occurring over the past four decades. This 2011 study follows another published in 2003, which concluded that industrial fishing has eliminated 90% of large ocean fish.^ As a consequence, as fishing efficiency has gone up, catch rates have gone down; only one successful catch is made per 100 longline hooks, as opposed to 10 per 100 at the onset of industrialized fishing technologies. Those fish that are lucky enough to avoid the longlines and gillnets are not numerous enough to reproduce sustainably. While UBC researchers do not foresee a totally fishless ocean by 2050, they do predict a massive ecological reorganization: without predator controls on the population growth of prey fish, oceans will be inhabited mostly by smaller species. Already, numbers of these prey fish have more than doubled over the past century, following the decline of their natural enemies. Although in some locales, such as the North Atlantic, herring and other small fish are in jeapordy due to unmonitored midwater trawling.^ And in the Pacific, populations of sardine, anchovy and herring are being taken in ever increasing numbers to feed cats, dogs, chicken and the growing numbers of farmed fish.*
This is cause for concern, as big predator species are vital to ecosystem balance.^ Without predatory fish, we can likely look forward to murkier, less diverse waters. As populations of certain small, foraging fish increase, so does the incidence of algal blooms. This is because the small foragers eat zooplankton, which in turn consume algae. The loss of predator fish may thus precipitate a deep green sea, robbed of oxygen by these suffocating algal blooms and rendered uninhabitable to most aquatic organisms.
Climate change, in conjunction with overfishing, will also pose a threat to ecosystem vitality. Heavier rainfall, predicted to occur mostly in tropical areas, may form a surface layer of warmer, fresher water that does not mix well with the denser, colder, and saltier layers below it. This stratification of the water column inhibits the circulation of deep water nutrients, which plankton – the base of the marine food chain – need to survive. Fewer plankton means less food for fish, affecting species growth all the way up the food web. Another problematic factor is ocean acidification, caused by higher levels of dissolved CO2 in the water. Coupled with warming, acidification may put excess stress on fish and further limit their growth. Those species that simply cannot handle the changes can be expected to move to more habitable waters. This includes over 50% of our current stocks, which may relocate by up to 40 kilometers per decade.
Sharks – of which 100 million are harvested yearly – are needed to maintain healthy seagrass beds and coral reefs through similar food web mechanisms that keep foragers in check.^ But since shark fins are a delicacy than can fetch up to $500 per pound, the economics of the trade are outweighing the need for conservation efforts. Only three species out of 350 – the white, whale, and basking sharks – are actually protected from the international fishing trade, and the fishing process itself is both cruel and wasteful: once the fins are removed, the shark is usually tossed overboard to slowly die. Sadly, sharks are now as endangered as they are unfairly demonized: they constitute the largest group of threatened marine animals on the World Conservation Union’s Red List.
Even though their flesh accumulates higher levels of toxic mercury and other contaminants, it’s the big, predator fish that are preferred on our dinner plates. Industrialized fishing practices have enabled our oceanic scouring, but these practices cannot be blamed any more than increasing dietary demand. Fifty percent of that demand increase can be attributed to East Asian countries, and 42% of that to China. Western nations are also guilty. In Britain, native waters are so overfished that restaurants and household kitchens must rely on imports six months out of the year.^ The depleted state of 70% of U.S. fisheries prompted Congress to tighten federal catch limits in 2006, but fish stocks are still in jeopardy as of 2011:
U.S. Dept of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service Office of Sustainable Fisheries.
Unless demand lessens and stricter regulations are imposed on the fishing industry, predator fish – and the ecosystems they help support – will have little chance for recovery. The continued existence of wild oceans depends on our willingness to change our palates. For links to more sustainable seafood choices, see: inspirationgreen.com/fish-seafood-guides
A list of commercial fishing methods, including their environmental impacts, at the Monterey Bay Aquarium website: www.montereybayaquarium.org
SeafoodWatch seafood reports on the statuses of both farmed and fish species, also from the Monterey Bay Aquarium website: www.montereybayaquarium.org
Forage Fish are declining as well:
*Forage Fish Should Stay in the Ocean: oceana.org