Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
John E. Graves
Eighty-five monitored sets were used to investigate the interactions of pelagic fishes with commercial pelagic longline gear in the western North Atlantic during the fall mixed species fishery north of Cape Hatteras, North Carolina, and the spring swordfish fishery in the southern Gulf of Mexico and northern Caribbean Sea. This dissertation incorporates four components: (1) direct analyses of longline gear behavior using small time-depth recorders, (2) comparisons of catch rates and mortality of all species caught on size 16/0 non-offset circle and size 9/0 straight-shank J-style hooks, including analyses of time-of-capture utilizing electronic hook time recorders, (3) an evaluation of post-release survival of white marlin captured by longline gear using pop-off satellite archival tags (PSATs), and (4) a description of two PSATs attached to white marlin and subsequently ingested by sharks. Data indicated that pelagic longline gear in the shallow coastal U.S. fishery is frequently in motion, even after hooks were presumed to have settled at depth. Effective fishing depths of the gear under several configurations were also shallower than predicted by commonly used catenary curve-based depth calculations. Catch rates between circle and J-style hook types were similar for most species, with only pelagic rays in the fall fishery showing an increased catch rate with J-style hooks. Yellowfin tuna and dolphinfish caught on circle hooks in the fall fishery were larger than those caught on J-style hooks. Most species were more commonly caught in the mouth with circle hooks rather than internally. A total of 28 white marlin were tagged with PSATs. Transmitted data from 17 of 19 reporting PSATs demonstrated survival following release. Estimates of post-release survival range from 60.7% (assuming that non-reporting tags were mortalities) to 89.5% (excluding non-reporting tags from the analysis). Two white marlin PSATs reported data consistent with predation or scavenging by sharks, including ingestion of the tags for seven and ten days respectively. This suggests that non-reporting PSATs may also be the result of unreported biological interactions.
© The Author
Kerstetter, David., "Description and evaluation of the United States coastal pelagic longline fishery interactions with target and non-target species in the western North Atlantic" (2005). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539616711.