Effects of Turtle Excluder Devices (TEDs) on Loggerhead Sea Turtle Strandings with Implications for Conservation

Abstract

All five species of sea turtles in United States waters are listed under the Endangered Species Act as threatened or endangered. A major source of mortality for these turtles is drowning in shrimp trawls; 70-80% of strandings of dead turtles on beaches are related to interactions with this fishery. In the late 1980s, the state and federal governments began requiring turtle excluder devices (TEDs) in trawl nets; TEDs allow turtles to escape the nets before they drown. To date, the effectiveness of TEDs in reducing sea turtle strandings has not been quantitatively assessed. In this paper, we report on a statistical analysis of strandings data for loggerhead sea turtles on South Carolina beaches from 1980-1993. These data are long term, based on excellent beach coverage and include eight years before TEDs were required, two years of intermittent use, and four years with TED regulations in place. Regression analysis of the natural log-transformed strandings data showed a good fit to the model (R2 = 0.88). The model had significant linear and squared trend terms suggesting the trawlers were sampling from a declining population (-5.3% per year), but the rate of decline has diminished. The analysis shows significant effects of the shrimp fishery in increasing strandings. The effect of TEDs in reducing strandings was also significant; TEDs reduce strandings by about 44% relative to the estimated effects of shrimp trawls without TEDs. If reductions in stage-specific mortality rates are at all similar to the observed reductions in strandings due to TEDs and other mortality sources do not intervene, population model predictions suggest that the outlook for loggerhead population recovery is good.