The 1997 Gulf and Atlantic Coastal Shark Assessment survey was conducted in the Gulf of Mexico and western North Atlantic coastal waters from Cabo Rojo, Mexico to Cape Hatteras, NC (see Map) onboard the NOAA Ship R/V OREGON II. Commercial style bottom longline gear was fished in depths of 5 to 30fathoms (see 1995 Shark Tagger Summary). A portion of the survey, conducted within territorial waters of Mexico (Leg II, U.S.-Mexico international boundary, southern limit of Texas to Cabo Rojo, Mexico), operated under auspices of the MEXUS-GULF Program and was coordinated with Instituto Nacional de la Pesca headquarters in Mexico City, Mexico.
Objectives of the survey were to: 1 ) assess the distribution and abundance of coastal sharks along the U.S. and Mexico coasts of the Gulf of Mexico; 2) collect biological and environmental data; and 3) tag and release sharks. Biological data for each capture included species identification, fork length (mm), total length (mm), fish condition (alive or dead), sex, whole weight (kg) and tag number if applicable. For some specimens, biological sampling included tissue samples for DNA studies, external parasites, collection of vertebrae for age and growth studies, and dissections to examine reproductive status and/or collection of internal parasites.
During the survey, 259 longline sets were completed (approximately 25,900 hook hours). Survey operations for Legs I, II, and III were in the Gulf of Mexico; Leg IV was along the southeast U.S. Atlantic coast (Figure 1). Leg I was conducted from south of Mississippi to offshore of Brownsville, TX. Leg II was conducted from offshore of Brownsville, TX to Cabo Rojo, Mexico (25 longline sets in Mexican waters). Leg III was conducted from south of Mississippi to the Florida Keys, FL, and Leg IV was conducted from offshore of Miami, FL to Cape Hatteras, NC. The survey along the Mexican coast from Cabo Rojo to the eastern Yucatan Peninsula was not completed due to circumstances requiring changes in the project objectives.
Shark captures composed 90% (926) of the total catch (1,030), with the remaining 10% classified as incidental catch (104). Of the 15 shark species captured, 4 species were small coastal sharks (74% of shark captures), 10 were large coastal species (26% of shark captures), and 1 was a pelagic species (shortfin mako, Isurus oxyrinchus, 0.11% of shark captures). The Atlantic sharpnose shark (Rhizoprionodon terraenovae, 88% of 681 small coastal shark captures) was the dominant small coastal shark, and the most dominant shark caught overall (65% of all shark captures). The dominant large coastal shark species caught was the sandbar shark (Carcharhinus plumbeus, 24.6% of 244 large coastal shark captures), followed by blacktip (C. limbatus, 23.8%) and tiger sharks (Galeocerdo cuvier, 22.1%).
The ratio of small coastal sharks to large coastal sharks and the dominant shark species often varied by area. The highest percentage of small coastal shark captures occurred between Florida and Cape Hatteras (during Leg IV) with small coastals composing 81% of shark captures. The highest percentage of large coastal shark captures occurred in the eastern Gulf of Mexico (during Leg III) with large coastals composing 53% of all shark captures. During the survey, 560 sharks were tagged and released (60% of shark captures).
Shark catches per unit effort (CPUE, expressed as sharks per 100 hook hours) were: 4.32 during Leg I (406 shark captures, 94 longline sets), 0.41 during Leg II (14 shark captures, 34 longline sets), 2.18 during Leg III (144 shark captures, 66 longline sets) and 5.57 during Leg IV (362 shark captures, 65 longline sets).