The population structure of the copepod, Pseudocalanus sp., on Georges Bank in February 1975 had distinct shifts from younger to older developmental stages in a clockwise pattern around the bank. It is hypothesized that this spatial pattern resulted from the interaction of copepod population dynamics and the mean circulation of sea water around Georges Bank. To test this idea, a combined physical/biological model is developed which simulates copepod population dynamics at each of a series of fixed spatial points around a hypothetical gyre. This simple physical scheme incorporates both advection and diffusion of copepods around the gyre. Rates of advection and diffusion are taken from the literature. Environmental influence on life history parameters (development rate, fecundity, and mortality) for Pseudocalanus sp. are found from laboratory experiments and from the literature. Spatial patterns generated by the model agree well with those observed from field samples. The results show that the hypothesis is possible thus providing a reasonable explanation for mechanisms generating these patterns. It is suggested that such mechanisms may contribute to much of the coarse and meso-scale (50 – 1000 km) heterogeneity in the distribution of marine zooplankton.