Island in the Stream: Oceanography and Fisheries of the Charleston Bump

The Charleston Gyre as a Spawning and Larval Nursery Habitat for Fishes

John J. Govoni and Jonathan A. Hare


Abstract.—The region of the outer continental shelf and upper slope, encompassed roughly by 32 and 33°N and 78 and 79°W, is unique within the southeastern Atlantic coast of the United States because of the frequent presence of large (amplitudes of 50-100 km), cyclonic eddies. These eddies develop continuously north of the deflection of the Gulf Stream at the Charleston Bump and decay downstream. The cyclonic circulation of these eddies brings nutrient-rich water from deep and off the shelf edge to near surface and results in enhanced primary production. Succession of Zooplankton assemblages, driven by enhanced primary production, might serve fish production by providing an exceptional, and more continuous food supply for larval fishes spawned in or entrained into eddies. In addition, larval fishes that risk entrainment into the Gulf Stream and consequent loss from local populations, can be retained on, or near, the shelf when embedded within these eddies. The residence of an eddy within the region ranges from a week to a month or two, while the larval period of most fishes ranges from weeks to months. The large-scale eddies in the region develop most frequently in winter when the Gulf Stream is in its strongly deflected mode, coincident with the spawning of a suite of commercially important fishes. Although the region of the Charleston Gyre has the potential to act as an important spawning and nursery habitat, published evidence of usage of the habitat afforded by large scale eddies in this region is weak. High concentrations of larval fishes occasionally occur in the region, but there is no indication of high concentrations of fish eggs. With its high primary and secondary production, succession of Zooplankton assemblages, and retention mechanism, the region of the Gyre may constitute an important spawning and nursery habitat for fishes, but more research aimed at assessing this potential is necessary.