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Chapter 7 - Demersal FishAtlantic wolfish, barndoor skate, cusk, and thorny skate.Of these five species, Atlantic halibut and barndoor skateare considered endangered by the IUCN and Atlanticwolffish and cusk are under status review by NMFS forpotential Endangered Species Act listing (NMFS 2009a).Ecosystem Interactions and Ecological DependenciesThe demersal species included in this assemblage arecharacterized by their close association with the seafloorfor critical life stages and activities including feeding, usageof juvenile nursery areas, and spawning. High ratesof productivity in the region provide an abundant foodsource for planktivores in the water column, while still allowingsignificant energy to reach the ocean floor to supportbenthic communities.The trophic ecology of demersal fish species in theNorthwest Atlantic is well studied. Many species arecharacterized as opportunistic generalists, feeding on avariety of prey items ranging from plankton to benthicmacroinvertebrates or fishes depending on life stage (Linkand Garrison 2002). Larval and juvenile life stages ofmany demersal fish are a significant food source for adultlife stages of species, and cannibalism is not uncommon.Many demersal fishes exhibit ontogenetic (size-specific)shifts in diet, switch among prey items according to theiravailability, and exhibit dietary preference for small pelagicfish.In contrast to other ecosystems, the food web of thenortheast United States Continental Shelf ecosystem ishighly connected and complex, consisting of weak speciesinteractions (Link and Garrison 2002). It has beeninferred that production in this region is tightly bound,with most of the fish production being consumed byother fish species (Sissenwine et al. 1982). These apparentenergetic constraints can result in relatively stablelevels of overall biomass and production of fish, althoughdramatic fluctuations at the individual species level areroutinely observed. Such fluctuations were observed onGeorges Bank in the mid- to late 1980s as populations ofelasmobranchs (skates and dogfish) increased in responseto significant declines in cod, haddock, and flounder populationsdue to fishing pressure (Fogarty and Murawski1998). Similar changes in trophic dynamics were observedin coastal portions of the Gulf of Maine when depletion ofcod and other large predatory fishes fundamentally alteredthe food web, leading to significant increases in lobsters,crabs, and sea urchins in the coastal zone (Steneck 1997).These studies and others demonstrate the degree to whichpopulations of some species in the assemblage (and othermarine species) are directly influenced by changes in therelative abundance of others.In addition to species-specific trophic interactions, manydemersal species in the assemblage display strong associationswith a range of benthic habitats during various lifestages. For example, survivorship of juvenile cod is knownto be higher in substrates with greater structural complexity,and it has been suggested that gravel substrate mayrepresent a limiting resource for the early life stages of codand haddock (Fogarty and Murawski 1998). Nearshorecoastal and estuarine habitats are especially important fora number of the Southern New England and mid-Atlanticspecies in the group. Atlantic croaker, summer flounder,spot, tautog, and winter flounder display obligate utilizationof these habitats (they use them by necessity), andmany others, including black sea bass and displayingfacultative (non-obligatory) use. Golden tilefish areknown to be important modifiers and creators of habitaton the outer Continental Shelf and along the slopes andwalls of submarine canyons, creating elaborate “pueblovillages” of burrows within clay substrates, presumablyto avoid predation (Able et al. 1982; Grimes et al. 1986).Tilefish burrows provide habitat for a variety of otherspecies, including crustaceans, lobster, conger eel, cusk,hake, and ocean pout.7-Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report