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

We present an objective method for identifying associations between environmental (habitat) conditions and the distributions of marine fishes 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 the distributions of four groundfish species (yellowtail flounder (Pleuronectes ferruginens, previously Limanda ferruginea), haddock (Melanogrammus aeglefinus), silver hake (Merluccius bilinearis), and Atlantic cod (Gadus morhua)) from trawl surveys of the eastern Scotian Shelf (northwest Atlantic) conducted in winter/spring (March) and summer (July) 1979-84. Haddock and silver hake maintained similar temperatures in winter and summer by changing their depth distributions (temperature-keepers), with haddock generally at cooler temperatures than silver hake. Yellowtail flounder (a depth-keeper) maintained similar depths between seasons while tolerating a wide range of temperatures and salinities. Atlantic cod were not consistently associated with particular depths in either spring or summer, and we were unable to distinguish between temperature or salinity as a single factor modifying their distributions, perhaps because of age-related effects. Identification of persistent habitat associations of marine fishes provides an opportunity to improve fisheries management procedures.