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Commercial Shark Fishery Observer Program

Final Report Abstracts

1994-1995 Final Report Abstract
Steve Branstetter1 and George Burgess2
1 Gulf and South Atlantic Fisheries Development Foundation, Inc.
2 University of Florida

To garner otherwise unobtainable information, and thus enhance the reliability of management strategies, observers aboard voluntarily participating commercial shark vessels documented a sample of the catch and effort of the southeast U.S. commercial shark longline fishery. In 1994 and 1995, three observers logged 351 sea days monitoring 276 longline sets during 96 fishing trips. Approximately 3,000,000 hook-hours of effort produced nearly 11,000 sharks of 26 different species; this translated to more than 115 metric tons of landings (2.3% of the U.S. Atlantic commercial shark landings for the two-year period). Two species - blacktip sharks (Carcharhinus limbatus), common inshore of the 10 fathom contour, and sandbar sharks (Carcharhinus plumbeus), dominant in deeper continental shelf waters - constituted 60-75% of the catch and 75-95% of the landings. About 15% of the large- coastal shark catch was released, and some cryptic mortality (catch that is used for bait or discarded) occurred in the fishery; landings accounted for approximately 90% of the total mortality on this stock. Nearly 100% of the small-coastal shark catch (dominated by the Atlantic sharpnose shark, Rhizoprionodon terraenovae) was landed or used for bait. Within a region, overall and depth-specific catch rates between years and seasons were, for the most part, not statistically different. For all regions combined, approximately 50% of the documented catch of sandbar and blacktip sharks was immature. Small sandbar sharks were more common inshore of the 10-15 fathom depth range, and almost all blacktip sharks were taken in these shallower waters. Approximately 70% of the sandbar sharks taken in the North Carolina area were female, but females only comprised 30-60% of the catch in Florida waters. For blacktip sharks, only about 25% of the North Carolina catch was female, whereas on both coasts of Florida, 50-60% was female. Over the course of a calendar year, only about 20-30% of the mature female sandbar sharks were documented as pregnant, but about 50% of the adult female blacktip sharks were pregnant. With only two years of data, no conclusive trends can be determined concerning the health of the shark stock, but given that much of the catch inside 10-15 fathoms is immature fish, or pregnant females, continued fishing pressure in nearshore (< 10 fm) waters may have substantial negative impacts on the stock; to the long-term detriment of the stock and fishery. Excluding these nearshore efforts, recruitment to the fishery is substantial by the time the fish are 135 cm FL (12 yr of age). Based on this age structure, a minimum size limit of perhaps 140 cm FL for sandbar sharks might be an appropriate management measure. Very preliminary estimates indicate that with such measures, which would equal approximately a 10% reduction in quota, the sandbar shark stock could increase in numbers with continued fishing.

Reprinted from: FINAL REPORT - MARFIN Award NA47FF0008 - "Characterization and comparisons of the directed commercial shark fishery in the eastern Gulf of Mexico and off North Carolina through an observer program" supplemented with INTERIM REPORT - S-K Award NA57FD0067 - "An expansion of an observer program to characterize and compare the southeast US directed shark fishery to include the east coast of Florida," March 1996.