Incidental capture and mortality of sea turtles in the industrial shrimp trawling fishery of northeastern Venezuela

Abstract

The incidental capture of sea turtles by industrial shrimp trawlers off eastern Venezuela is documented, based on data gathered by on-board observers from February 1991 through November 2000. A total of 275 trips were made, with a total of 55,992 h of trawling using either one or two normal nets of 20-m headrope length, equivalent to 59,744 h std. net^–1 of 30.5 m upper rope length. In total, 63 turtles were captured: 20 Eretmochelys imbricata, 20 Chelonia mydas, 15 Caretta caretta, and 8 Dermochelys coriacea. All these species showed a wide distribution along the central Caribbean Sea and Atlantic coasts of Venezuela, but they were always caught in areas close to shore and not deeper than 82 m; the distribution of D. coriacea was more concentrated towards the Atlantic zone. The estimated CPUE for all four species, using non-standardized effort values, was 0.0011 ± 0.0003 turtles h^–1 std. net, equivalent to one turtle per 930 ± 11 h std. net. The variation in captures throughout the year was not significant (χ² = 1.29; P = 0.73), except for D. coriacea, which was only caught between January and May. No significant difference was observed between the capture of turtles during the day or night. Direct mortality ratio reached 19 ± 9.7%; the actual ratio of mortality caused by incidental capture is not known. Most individuals caught by Venezuelan trawlers were juveniles that most probably use the area as feeding grounds. Considering an average effort by the fleet of 310,000 ± 16,500 h std. net yr^–1, an estimate of turtle capture before the use of turtle excluder devices was made mandatory in 1994 would be about 330 ± 4 ind yr^–1, with an associated direct mortality of 63 ± 30 turtles. This capture rate would be the lowest among the countries where similar evaluations have been performed (Australia, Colombia, Costa Rica, and USA). Key words: size structure, CPUE, distribution, Caribbean Sea.