Eating fish presents a very different environmental challenge than does eating meat farmed on land. Greenhouse gases aren’t as much of a problem, although the energy consumed by fishing boats and by production of fish does contribute to climate change. However, the biggest problem is overfishing. Radar, GPS, and other advanced technology have allowed us to systematically destroy large fish populations, so that “75 percent of major fisheries are fully exploited, overexploited, or depleted" (Clark & Clausen). We have been “fishing down the food chain,” which means that large, predatory fish are more rare, and what used to be considered “trash fish,” such as tilapia are becoming a mainstay of menus.
With today’s massive dragnets, an additional problem is bycatch; endangered species such as seals, porpoises, and many others, are caught along with the intended targets: “The average trawling operation throws 80 to 90 percent of the sea animals it captures as bycatch overboard” (Foer). Indeed, “Many scientists predict the total collapse of all fished species in less than fifty years” (Foer)—the empty ocean is a real possibility.
As our oceans, lakes, and rivers run out of fish, the alternative is aquaculture, or fish farms. Unfortunately, current aquacultural practices are not environmentally friendly. Fish are crammed together in cages, often swimming around in their own wastes, and given antibiotics to avoid disease. Farmed salmon has been shown to have high levels of PCBs and insecticides (Hamerschlag); however, its greenhouse emissions are lower than most livestock, at 4.14 kilograms of CO2 equivalent per kilogram of edible salmon (Hamerschlag and Venkat). Farmed fish are also fed fishmeal, which means that fish low on the food chain are caught, increasing the marine impact, including bycatch (Clark & Clausen). The impact of the menhaden, a type of small fish caught to be fed to farmed fish, is also great, as this critical little fish is facing severe threats.
Healthwise, fish are a lean source of protein, as well as the omega-3 fatty acids that help the heart. However, fish also contain mercury, a poison that accumulates up the food chain and can damage the brain and nervous system (Griesbauer). Mercury is particularly dangerous for pregnant women; among other risks, it can result in children born with brain damage. Tuna and sea bass are loaded with mercury, while shark and swordfish are even worse—another reason to recommend such fish as tilapia low on the food chain. Anchovies, sardines, and salmon are also low in mercury.
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