Life history and production of three amphipod species on Georges Bank

Abstract

As part of the Georges Bank Benthic Monitoring Program [which monitors effects of oil exploration and drilling] size-frequency analysis was used to study the life history and production of 3 benthic amphipod species: Ampelisca agassizi, Unciola inermis and Ericthonius fasciatus. Abundant over large areas of Georges Bank, these amphipods are important prey of yellowtail flounder. From benthic grab samples collected quarterly during 1981-1983, > 200 individuals of each species were measured from each sampling date. The computer program NORMSEP was used to separate the length-frequency distributions into cohorts. Growth and mortality rates were determined by following cohorts through time; production was calculated as the sum of growth increments. Differences in the populations dynamics of the 3 spp. are exemplified by the annual production-to-biomass ratios. E. fasciatus has the highest P/B [productivitly to biomass] ratio (4.4), followed by U. inermis (2.5) and A. agassizi (1.5). These results, the 1st direct production estimates for benthic macrofaunal species on Georges Bank, are compared to production estimates for other marine amphipod species. Amphipod production rates on Georges Bank appear to be as high as production rates of related near-shore species.