Rockfish Caught Near Salmon Farms High in Mercury
Mercury concentrations are elevated in copper rockfish and quillback rockfish taken near salmon farms along British Columbia’s coast. Rockfish sampled within 750 m of nine salmon farms, where native communities traditionally harvest seafood, had mercury levels ranging from 1.7 to 3.3 times higher than rockfish found over 3 km away from operating fish farms in the same area.
Although not surpassing Health Canada’s guideline for mercury consumption, the levels in rockfish near salmon farms are high enough to warrant that women and children limit how much rockfish they eat.
Mercury builds up near salmon farms in fish feed and waste. It is also biologically more available underneath fish-pen nets where ocean sediments become depleted of oxygen. Near one-third of the farms sampled, mercury concentrations in rockfish are further exacerbated by the fish feeding higher than usual up the food chain, preying more on other fish than on invertebrates.
These environmental effects are long-lived because of how mercury behaves in the environment and accumulates in rockfish. Fallowing fish farms for six months is not enough to lower mercury levels in rockfish by any more than 15%.
Adrian M.H. deBruyn, Marc Trudel, Nicola Eyding, Joel Harding, Heather McNally, Robert Mountain, Craig Orr, Diane Urban, Sergei Verenitch and Asit Mazumder. 2006. Ecosystemic Effects of Salmon Farming Increase Mercury Contamination in Wild Fish. Environmental Science and Technology. 40 (11): 3489-3493.