Effect of artificial light on marine invertebrate and fish abundance in an area of salmon farming

Artificial light can change the behaviour of aquatic organisms, although the direction of response can be species and life-stage specific. Open net-pen salmon farms in British Columbia, Canada, routinely illuminate their net-pens during the winter and spring, with unknown consequences on the abundance and distribution of marine fish and invertebrates. Paired lit and control samples consisting of plankton hauls and purse seines were made around a 400 W underwater light such as those used on salmon farms. On lit nights, invertebrates were marginally more abundant, while fish larvae and juvenile and adult fish were significantly more abundant. In particular, the invertebrate taxa Gastropoda and Bivalvia were significantly more abundant on lit nights, as were the fish species Pacific herring Clupea pallasi, sand lance Ammodytes hexapterus, threespine stickleback Gasterosteus aculeatus, soft sculpin Psychrolutes sigalutes, and great sculpin larvae Myoxocephalus polyacanthocephalus. These results suggest that lights commonly used in open net-pen aquaculture may increase the abundance of some fish species around pens, thereby increasing the probability that farmed fish and wild species directly and indirectly interact in coastal marine environments.