Spatial and dietary overlap in the Georges Bank groundfish community

Abstract

Patterns in spatial and trophic resource partitioning in the fish community of the Georges Bank region are identified, accounting for size-based changes in diets. During autumn and spring, this community is divided into geographic assemblages of species that have high spatial overlap. Similarity in spatial distribution is primarily related to similarity in depth preferences, and seasonal differences in species composition within assemblages are related to migrations. There is also important trophic structure within the Georges Bank community separating predators based upon prey size and location in the water column. Ontogenetic changes in diets are an important feature of the trophic structure in this system, particularly in the major piscivores. Seasonal changes in trophic structure reflect both predator and prey migrations. Dietary overlap among predator types is independent of either spatial overlap or depth preferences. There is spatial segregation within trophic guilds, and this spatial partitioning reduces the potential for exploitative competition within this community. Given the observed spatial patterns in trophic structure, the geographic assemblages on Georges Bank may be considered ecologically distinct functional units within this ecosystem.