Midshelf fronts in the South Atlantic Bight and their influence on seabird distribution and seasonal abundance

AbstractRelationships of seabird distribution and abundance to continental shelf fronts off the southeastern United States were studied during a 15-month period in 1983–1984. Surface thermal fronts occur in the middle shelf domain (20–40- m depths) on the continental shelf of the South Atlantic Bight (Cape Hatteras, North Carolina, to Cape Canaveral, Florida). Midshelf fronts propagate south of Cape Hatteras following coolings events and persist from October through March. The monthly mean abundance of seabirds in the midshelf domain was correlated with the frequency of occurrence and extent of these fronts. Seabird abundance within the midshelf domain peaked during fall and winter when fronts were also most numerous and extensive (attaining 1,800-km lengths). Seabirds aggregate within 10 km of the front, with greatest densities (> 150/km2) on the shoreward side. Seabird guilds displayed different affinities for the fronts. Zooplanktivorous phalaropes (Phalaropus) had a clumped distribution, highly correl...