Effect of sea cage aquaculture on the length, weight, and condition of wild Atlantic cod Gadus morhua

Abstract

Wild fish have been shown to associate with sea cage aquaculture and consume waste feed; however, little is known about the effects of waste feed consumption on wild fish. We used Atlantic cod Gadus morhua collected in the direct vicinity of sea cages and reference Northwest Atlantic Fisheries Organization divisions, either outside the direct vicinity (‘local division’) or completely removed from aquaculture (‘outside divisions’), to compare length, weight, and condition for cod ages 2 to 4. Concentrations of vegetable oil-based fatty acids (linoleic acid and α-linolenic acid) were then used as biomarkers for waste feed consumption to determine their role in explaining differences in length, weight, and Fulton’s condition index among cage-associated cod. Age 2 cage-associated cod were in lower condition than age 2 cod from the local division and lighter than age 2 cod from all outside divisions. Age 3 cage-associated cod were comparable to age 3 cod from the local division but in lower condition than age 3 cod from all outside divisions. However, age 4 cage-associated cod were longer and heavier than age 4 cod from the local division, but in lower condition than age 4 cod from 2 of 3 outside divisions. Additionally, there were positive relationships between fatty acid concentrations and length and weight for age 2 cage-associated cod, but no significant relationships for age 3 or 4 cage-associated cod. Results suggest the effects of waste feed consumption are contradictory but not consistent enough to disrupt established growth and condition patterns among divisions.