Dynamics of the shark community in the Mid-Atlantic Bight

Abstract

Inventory biodiversity indices such as species richness, distribution of species’ abundances or evenness in communities, and those that represent functional characteristics provide foundational information that can be used to formally evaluate the ecological role species fulfill within ecosystems. Describing changes in the dimensions of biodiversity relative to spatiotemporal and environmental gradients facilitates more refined and integrated views of community dynamics. This study synthesized fisheries-independent bottom longline survey data collected from 1990 to 2018 to elucidate patterns in six inventory biodiversity indices across temporal, small-scale spatial, and thermal domains for the shark community inhabiting the Mid-Atlantic Bight. Model-based predictions over years showed marked increases since the mid-2000s in several indices and were suggestive of an expanding community in terms of species richness, biodiversity, relative abundance, functional traits, and size composition. Annual relative evenness predictions were fairly constant and indicative of persistent maintenance in the distribution of community abundance across taxa through time. Changes in the biodiversity indices were also evident across a fairly small spatial area and in response to bottom water temperature, although patterns were less prominent when compared to interannual trends. The results of this study complement single-species population analyses by providing a community-level perspective, and offer positive indications that the shark community off the U.S. east coast has become more robust over the past several years.