This article originally appeared in The Shark Tagger-1998 Annual Summary
Members of the Apex Predators Program conducted three spring longline surveys on board the NOAA Ship Delaware II and R/V Pelican (1996) along the Atlantic coast during 1989, 1991, and 1996. The 1989 survey was conducted between Tampa Bay, FL and southern New England (Cruise DE II 89-03). The 1991 survey (Cruise DE II 91-06) was conducted between Miami, FL and southern New England using the same fishing methods. The third survey, conducted in 1996 (Cruise Pelican 96-01), repeated stations from the first two surveys in the region from Key West, FL to Delaware Bay, DE, between 5 and 40 fm. The cruises were essentially the same with respect to biological studies of sharks. However, the gear and soak times were altered in 1996 to more accurately represent that of the commercial large coastal shark fishery. The 1998 survey was basically a repetition of the 1996 survey.
The objectives of the 1998 survey, like 1996, were to: 1) investigate the distribution, abundance and species composition of sharks; 2) collect baseline catch per effort data; 3) tag sharks for movement and distribution studies; 4) inject tagged sharks with tetracycline for age validation studies; 5) collect biological samples for age and growth, food habits and reproductive studies; and 6) collect morphometric data. This information will continue to be used in conjunction with data from previous surveys to assess the populations of coastal sharks in the Atlantic Ocean.
The survey was conducted from 13 April to 29 May 1998 on board the NOAA Ship Delaware II. Ninety-one sets were completed between Key West, FL, and the Maryland/Delaware border. Of 917 sharks caught, 857 were tagged and released, 37 were brought on board and dissected for biological research and 23 were lost. The majority of sharks caught were sandbar (71%) and tiger sharks (15%). No other single species represented more than 4% of the catch.
Apex Predators Program personnel, in conjunction with the Canadian Department of Fisheries and Oceans, are continuing their studies on the age and growth of the porbeagle shark and expanding research to include movements, reproduction, and food habits. To date, we have vertebrae from 140 porbeagle sharks, ranging in size from 2.5' (birth) to 7.9' FL. Preliminary analyses of these vertebrae show that they have distinct rings. Several hundred porbeagle sharks have also been tagged, primarily by Canadian commercial fishermen and observers. The 1998 cruise was designed to target porbeagles off the coast of Maine and possibly Canada for the primary purposes of tagging as many porbeagles as possible and injecting them with tetracycline. The validation of vertebral band periodicity using the backbones of tetracycline injected sharks is vital to our age and growth study.
The cruise was conducted from 19 to 30 October, 1998 offshore of Massachusetts and Maine on the U.S. Atlantic coast. The objectives of the cruise were to: 1) tag and inject porbeagle sharks with tetracycline; 2) place archival tags on porbeagles; 3) collect biological samples for age and growth, food habits and reproductive studies and 4) collect morphometric data.
A total of 130 sharks, representing 4 species, were caught on 12 longline sets. Of these, 121 were tagged and released (43 injected), and 9 were released untagged or lost. Sharks represented 96% of the total catch of which blue sharks (58%) were the most common, followed by porbeagle (43%), common thresher, spiny dogfish and unknown sharks (2% each); additionally two skates and three bluefish were caught. Archival tags were attached to the first dorsal fins of five porbeagles (see related article). The data collected on this cruise will be combined with data from previous cruises and used to study the life history of this species.
The NMFS Southeast Fisheries Science Center (Mississippi Laboratory) conducted longline survey operations aboard the NOAA Ship Oregon II from 7 July to 22 September, 1998 in the Gulf of Mexico and Caribbean Sea along the coasts of Mexico, Cuba and Navassa Island. Commercial style monofilament bottom longline was the primary fishing gear (see 1995 Shark Tagger for details). During Leg III, pelagic gear was used in addition to the bottom gear. Gear configuration for the pelagic sets consisted of a high flyer followed by five evenly spaced hooks, a bullet float alternating every five hooks until 50 hooks were out, after which a second high flyer was attached. Drop lines of 164, 328, or 492 feet were attached at the high flyers and float lines. To settle the mainline to the desired fishing depth, a weight was attached to the mainline at a depth corresponding to the drop line depth beneath the first high flyer. Additional gear modifications during pelagic work included the addition of an8-10" steel leader (200 lb. Test) to the monofilament gangions.
The primary objectives of the survey were to: 1) assess the distribution and abundance of coastal and pelagic sharks; 2) collect biological and environmental data; 3) tag and release sharks; 4) utilize underwater video cameras to assess reef fish species composition and reef habitats at Navassa Island; and 5) utilize a fisheries acoustic system (FAS) to collect acoustic data and bathymetry at Navassa Island.
During the survey, 216 sites were sampled, 134 by bottom longline, 76 by pelagic longline, three by underwater video with FAS, and three by FAS bear only. A total of 147 fish were caught by longlining. Sharks comprised 45% of the total while 55% was incidental catch. Eighty-five percent of the sharks caught were tagged and released; the rest were brought on board for examination.
Legs I and II were conducted in Mexican waters between the US/Mexican border along coastal Mexico to the Bay of Campeche and coastal Yucatan. A total of 110 bottom longline sets caught 21 sharks (0.19 sharks/100 hook hours (hkhrs)) consisting of 11 large coastal and 9 small coastal sharks and 50 incidental fish (0.45 incidentals/100 hkhrs). Most of the sharks captures (76%) occurred along the Campeche Bank between 93° W and 90° W. The blacktip shark was the most common large coastal shark (4), the Atlantic sharpnose was the most common small coastal shark (7) and the southern stingray was the most common incidental fish (20).
Leg III was conducted in Cuban waters and around Navassa Island. Nineteen bottom longline sets produced 35 sharks (1.32 sharks/100 hkhrs) consisting of 16 large coastal and 9 small coastals and 18 incidental fish (0.95 incidentals/100 hkhrs). There were no dominant large coastal species caught but three each of scalloped hammerhead, tiger, Caribbean reef, and nurse sharks were caught. The dominant small coastal shark was the smooth dogfish (8) and the dominant incidental fish was the amberjack (6).
Seventy-six pelagic longline sets yielded 9 sharks (0.12 sharks/100 hkhrs) of 3 species, all of which were large coastals and 12 incidental fish (0.15 incidentals/100 hkhrs). The three shark species caught were silky (7), dusky (1), and scalloped hammerhead (1). The dominant incidental fish was the great barracuda (9).
The initial survey design for Cuban waters consisted primarily of bottom longline; however, due to the steep narrow continental shelf in most areas, pelagic longlining was thought to be the better sampling method. Areas conducive to bottom longlining were restricted to isolated locations along the southeast coasts (Caribbean and Atlantic) and an area along the north coast from 78° W to 82° W. Strong oceanic currents were prevalent throughout most of the survey area.
Five additional bottom longline survey sites were selected around the Navassa Island's perimeter and, when possible, parallel to depth contours. Ten sharks of 3 species were caught including scalloped hammerhead (7), smooth dogfish (2), and bull shark (1). The largest shark catch (6), occurred at the westsouthwest station. Incidental catch from all longline stations included one misty grouper, one silk snapper, and one great barracuda.