Fishmeal in Aquaculture
Most fishmeal and fish oil is manufactured from anchovies, sardines, capelin, and sand eels, and some of the fisheries that target these species are considered to be well-managed. But not all fishmeal is sourced this way. In Thailand, most shrimp farmers buy less expensive fishmeal produced from marine life captured by local bottom trawlers, vessels that drag heavy nets along the seafloor, catching large volumes of untargeted marine life and at times damaging fragile seafloor habitats. There is a range of scientific opinion about exact conversion ratios, but most fisheries experts agree that the process of raising salmon and other carnivorous species consumes considerably more fish protein than it produces, adding more pressure on over-exploited ocean fish populations.
Some scientists working with the aquaculture industry argue that raising carnivores has not increased the total volume of fish being “officially” targeted for producing fishmeal and oil products, which are also used to feed swine and poultry. However they acknowledge that the percentage used for aquafeeds is steadily growing, and at the current growth rate, the aquaculture industry will require volumes in excess of what the oceans can sustain. At the current growth rate of the industrial sector farming carnivorous fish species, the United Nation's FAO reports that fish populations targeted for fish oil could be depleted by 2015. Fishmeal resources could be depleted by 2030. There is new evidence in some regions that “biomass” fisheries, which capture ocean fish for fishmeal, have begun to destabilize the marine food web with negative impacts on marine wildlife.
There are also food safety issues. Increasing levels of ocean pollution have begun to contaminate different types of seafood like tuna and swordfish with dangerous levels of mercury. Pollution has also resulted in the contamination of fishmeal and fish oil with PCBs and dioxins, which are known to cause cancer. These toxins tend to bio-accumulate at more dangerous levels in the fatty tissues of fish that are higher on the marine food chain (fish that eat other carnivorous fish). The results of a comprehensive sampling of farmed and wild salmon products in supermarkets across the U.S. and Europe has shown a much higher concentration of PCBs and dioxins in farmed salmon. This is partly because wild salmon naturally forage on a variety of marine life over a large area, much of which is lower on the marine food chain. The salmon aquaculture industry contends that the toxins in farmed fish are within ranges considered safe by FDA standards, however there is considerable disagreement between scientists as to whether these standards accurately reflect the true health risk. FDA standards are based not only on health hazards but also on trade and commerce considerations. A much more rigorous standard used by the U.S. Environmental Protection Agency, and based solely on health considerations, indicates a much higher risk associated with eating farmed salmon.