The distribution and abundance of pelagic gammarid amphipods on Georges Bank and Nantucket Shoals

In this study, long-term, broad-scale zooplankton survey data were used to estimate the temporal and spatial distribution and abundance of gammarid amphipods present in the water column on Georges Bank. Delta-mean abundances computed from 10 years of data showed that gammarid amphipod abundances peaked in summer and again in fall. The amphipods were also most numerous in water less than 50 m deep. The statistical tests employed revealed no conclusive evidence for diurnal vertical migration. Interannual delta-mean abundances fluctuated approximately 5-fold between 1977 and 1986, ranging from 217 to 1181 amphipods 100 m−3. Peak amphipod biomass occurred in July and was estimated to be 2.8 kcal m−2. Using production-to-biomass ratios from the literature, mean annual production of amphipods in these samples was estimated to be between 1.6 and 9.8 kcal m−2. Production in shallow areas was especially high, 22 kcal m−2 year−1.