Abundance and spatial distribution of copepods on Georges Bank during the winter/spring period

Abundant copepods on Georges Bank during the winter–spring period (January–June) 1995–1999 were Calanus finmarchicus, Metridia spp. (primarily M. lucens), Pseudocalanus spp., Oithona spp (primarily O. similis), Temora longicornis, Centropages typicus, and C. hamatus. The first four taxa had off-bank sources (Group I) while the last three (Group II) had on-bank sources. All Group I taxa were relatively low in abundance in January and then increased in abundance throughout the sampling period. C. finmarchicus and Metridia spp. showed similar changes in age structure with large numbers of nauplii initially, a maturation of the population in April, followed by a decline in nauplii in May and a resurgence in their numbers in June. These species never achieved high abundance on the shallow crest region of the Bank and became very low in abundance there during May and June. By contrast Pseudocalanus spp. and Oithona spp. increased in abundance throughout the sampling period and, although they were lower in abundance on the crest during winter (January–March) and early spring (April), were able to establish populations there and became abundant during May and June. Group II taxa were low in abundance during winter (C. typicus was abundant initially but declined through April) and did not begin to increase until spring (April–June). Their populations were centered over the crest of the bank indicating a local source, either from resting eggs, or because of high egg production rates due to the higher chlorophyll levels there.