Persistence of Demersal Fish Assemblages Between Cape Hatteras and Nova Scotia, Northwest Atlantic

摘要

Persistent spatial boundaries and species membership of groundfish assemblages between Cape Hatteras and Nova Scotia from 1967 to 1988 were described based on Northeast Fisheries Science Center autumn bottom trawl surveys. Responses of several of those assemblages to perturbation by fisheries were also described. Cluster analysis was used to identify site groups with similar species composition and species groups with similar spatial distributions for each year. Assemblage responses were tracked by subregion over time, based on mean and percentage of total-biomass-per-tow by species and indices of species diversity. Six major site groups were defined with cluster analysis in most years. Major differences in site group boundary patterns were observed between northern site groups (Scotian Shelf, Gulf of Maine, Georges Bank) and southern site groups (Northern Mid- Atlantic Bight, Southern Mid-Atlantic Bight and Deepwater). Northern site groups were characterized by sharp boundaries which persisted in the same area from year to year and corresponded to depth features. Boundaries of southern site groups shifted from year to year probably reflecting an increased influence of temperature-related oceanographic features. Membership in major species groups was highly persistent in time. Assemblages concentrated in northern subregions exhibited strong persistence in terms of spatial distributions as well. Although species group affiliations have persisted over time, the response of species groups to fishery perturbation varied among groups. Assemblages concentrated in northern regions did not appear resilient under fishery perturbation in the Gulf of Maine and Georges Bank subregions. Although comparable data were unavailable to characterize fishery perturbation in the Mid-Atlantic Bight area, during the same period that abundance of northern species groups continued to decline or remained at low levels, some migratory or potentially temperature-responsive species groups appeared to have extended their distributions northward, increased abundance, or both. Because many of these species are piscivorous and relatively underexploited, the result may be the potential addition of trophic linkages among assemblage groups as predator-prey interactions. Reversibility of fishery effects on productivity of less resilient assemblages will depend on the strength of trophic linkages both within and between assemblage production units that previously may have been uncoupled or only loosely coupled.