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Chapter 7 - Demersal Fishrepresenting an important center of distribution. Thesespecies include Acadian redfish, Atlantic cod, Atlantichalibut, Atlantic wolfish, American plaice, cusk, haddock,and pollock. Distribution of all other species within theassemblage is limited to the western side of the Atlantic,with the exception of spiny dogfish noted above (Colletteand MacPhee 2002).Analysis of species distribution usingNational Marine Fisheries Service(NMFS) bottom trawl survey dataand other sources reveals distinct differencesin species abundance, distribution,and composition within theNorthwest Atlantic region itself, withGeorges Bank representing a significanttransition zone between colderwaterspecies to the north in the Gulfof Maine and more temperate speciesin Southern New England and theMid-Atlantic. According to Cook andAuster (2007), there appears to bea reasonably strong consensus aboutthe existence of five distinct biogeographicregions on the ContinentalShelf of the eastern United States andNova Scotia, including the Scotian Shelf/Grand Banks,Gulf of Maine, Georges Bank, Southern New England,and the Mid-Atlantic Bight. Each is characterized by aunique combination of oceanographic conditions, fishspecies assemblages, and a wide variety of invertebratetaxa. The boundary at Cape Cod appears to be so strongthat some authorities consider it to be a break betweentwo major provinces, the Eastern Temperate and WarmTemperate (Cook and Auster 2007). This transition zoneat Georges Bank was also recognized by researchers studyingbenthic macroinvertebrates in the Northwest Atlantic,south of the Scotian Shelf. They found that the large majorityof species off Nova Scotia and in the Gulf of Maineconsists of boreal forms, whereas a significant componentof the Georges Bank assemblage is temperate transitionalor Virginian species because of the area’s higher seasonalmaximum temperatures (which preclude reproductionand/or growth of many subarctic or boreal species)(Theroux and Grosslein 1987).The most recent peer reviewed stock assessments foundthat ten of the demersal species included in the stock assessmentare overfished (less than half of biological goalsfor population size ) and eight are subject to overfishing(fishing mortality rates exceed target levels) (NEFSC2008). However, several species that were once severelydepleted are successfully rebuilding, including Acadianredfish, haddock, and summer flounder (NEFSC 2008;ASMFC 2009). Trends in relative abundance for each ofthe 32 species varied. While many species in the assemblageare declining, some are holding steady and othersare increasing. These trends are often specific to differentportions of the species’ ranges.A number of demersal fish species included in this assessmenthave been identified as Species of Concern. NMFSdefines these as species about which they have some concernsregarding status and threats, but for which insufficientinformation is available to indicate a need to listthe species under the Endangered Species Act. Species ofConcern included in the assemblage are Atlantic halibut,© Norm DespresNorthwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 7-