Factors affecting the seasonal abundance, composition and diversity of fishes in a Southeastern New England estuary

Abstract

Fish communities in the Slocum River, Buzzards Bay, Massachusetts were sampled over a 2-year period. Physical variables were measured when each of the 221 seine hauls were taken. A total of 54 species representing 36 families and comprising 18 913 individuals was collected. The measures of species diversity were computed for each month and the physical and biological data were subjected to factor analysis. The Slocum River estuary is dominated by a few resident species that are common in similar habitats along the northern mid-Atlantic states. The number of individuals increased with seasonal increase of temperature but this relationship was only approximate. The mean number of species per seine haul per month was more closely associated with temperature. The reciprocal of Simpson's index, SI′, peaked during the spring and fall. The low diversity during the summer was probably due to the invasion of large numbers of a few anadromous species. The high autumn diversity is caused by invasion of a small number of several expatriate tropical species. Within the estuary salinity influences the composition and diversity of the fishes. Station 1, which was an essentially freshwater habitat, produced all of the freshwater species and station 4, which was an essentially saltwater habitat, produced mostly stenohaline saltwater species. The diversity indices were lowest at these two stations. In contrast, stations 2 and 3 varied most in salinity and tended to be the most diverse. Factor analysis further reduced the large quantity of data and somewhat simplified the handling and the interpretation of the information. The loadings per year were reasonable associations of physical and biological parameters. Temperature was overall the most important physical factor while salinity was most important within seasons. The other physical variables measured were generally intercorrelated with temperature or with salinity and had by themselves no discernible effect on the abundance, composition, or diversity of the fishes.