IDENTIFYING HABITAT ASSOCIATIONS OF MARINE FISHES USING SURVEY DATA -AN APPLICATION TO THE NORTHWEST ATLANTIC

We present an objective method for identifying associations between en vironmental (habitat) conditions and the distributions of marine fishe s using survey data. The method tests the null hypothesis of a random association between fish distribution and habitat conditions. We apply this method to bottom depth, temperature, and salinity data and to th e distributions of four groundfish species (yellowtail flounder (Pleur onectes ferruginens, previously Limanda ferruginea), haddock (Melanogr ammus aeglefinus), silver hake (Merluccius bilinearis), and Atlantic c od (Gadus morhua)) from trawl surveys of the eastern Scotian Shelf (no rthwest Atlantic) conducted in winter/spring (March) and summer (July) 1979-84. Haddock and silver hake maintained similar temperatures in w inter and summer by changing their depth distributions (temperature-ke epers), with haddock generally at cooler temperatures than silver hake . Yellowtail flounder (a depth-keeper) maintained similar depths betwe en seasons while tolerating a wide range of temperatures and salinitie s. Atlantic cod were not consistently associated with particular depth s in either spring or summer, and we were unable to distinguish betwee n temperature or salinity as a single factor modifying their distribut ions, perhaps because of age-related effects. Identification of persis tent habitat associations of marine fishes provides an opportunity to improve fisheries management procedures.