Long term temporal perspectives for the demersal fish assemblages of Georges Bank with implications for management and modeling

Graduation date: 1983Questions of assemblage persistence, resiliency arid continuity in time were investigated with data from seasonal bottom trawl surveys conducted by the Northeast Fisheries Center, Woods Hole,\ud Massachusetts, from 1963-1978. Cluster analysis proved to be a useful statistical method for delineating assemblage boundries and corresponding resident demersal fish components from Georges Bank, northeastern coast, USA. Assemblages were continuous and persistant over the long term and changed spatial configuration only slightly on a seasonal basis. Responses of assemblage species\ud ranged from mild to severe with respect to declines in biomass, numerical density and changes in relative abundance. Assemblage directional changes were triggered by intense fisheries during\ud this time period as well as inherent trophic dynamics of component species. This study has potentially important multispecies management connotations and the assemblage concept is a useful potential operational definition or working hypothesis framework for further applications of management and modeling. Linear programming analyses with catch maximization objective functions showed that the goal of attaining total summed quotas within specific assemblages was highly dependent on species composition, relative abundance and distribution. A multispecies model of the shallow assemblage on Georges Bank was constructed to answer specific questions concerning the assemblage species composition changes we had observed. We were interested in determining\ud whether observed trends in species composition and abundance in this assemblage could in part be explained by simple ecological mechanisms. Results from model simulation runs indicate that competition and predation could account for some of the variability in biomass that we had observed in the shallow assemblage. These findings suggest that interspecific interactions may be important determinants of fish population abundance in this type of marine assemblage