Study

The impact of turtle excluder devices and fisheries closures on loggerhead Caretta caretta and Kemp's ridley Lepidochelys kempii strandings in the Gulf of Mexico, Texas, USA

  • Published source details Lewison R.L., Crowder L.B. & Shaver D.J. (2003) The impact of turtle excluder devices and fisheries closures on loggerhead and Kemp's ridley strandings in the Western Gulf of Mexico. Conservation Biology, 17, 1089-1097

Summary

Since 1980, The Sea Turtle Stranding and Salvage Network has monitored marine turtle strandings along the Texas coast, USA. High numbers of strandings in the early to mid-1980s, attributed in part to turtles being trapped and drowning in shrimp trawl nets, prompted regulations that required turtle excluder devices (TEDs) on shrimping vessels. However, following TED implementation in 1991, strandings in the Gulf of Mexico increased. In order to understand why, the efficacy of TEDs and other management actions (e.g. fisheries closures) on loggerhead Caretta caretta and Kemp's ridley Lepidochelys kempii turtle populations was evaluated by analyzing a long-term, stranding data set.

The Sea Turtle Stranding and Salvage Network data set contains records of turtle strandings on the Texas coast from 1980 to the present. For the purposes of the analyses, the following were excluded: incidental turtle captures by fishing vessels; turtles recovered from power-plant intakes; strandings of captive-reared or headstarted turtles; and strandings of turtles <10 cm carapace length.

The data set used (1986-2000) included 1,795 and 1,279 strandings of loggerhead and Kemp's ridley turtles, respectively.

Evidence of population growth independent of nest counts by identifying changes in the size distribution of all stranded turtles were sought, and shrimping variables (including the implementation of TEDs in 1991 and subsequent measures of compliance) incorporated.

The number of annual strandings increased dramatically from around 50-60 individuals of each turtle species in the years subsequent to introduction of the TED implementation (1991-1993) to around 180 for loggerhead and 205 for Kemp’s ridleys in 1994. Average annual strandings of loggerhead and Kemp's ridleys increased by 51% and 22%, respectively, between 1986–1993 and 1994–2000.

Analyses of the 1986 to 2000 data set suggests that both sea turtle population growth and increased shrimping activity have contributed to the increases in strandings around the Texas coast. Compliance with TED regulations was a significant factor in accounting for annual stranding variability i.e. low compliance was correlated with high levels of strandings.

The study projections suggest that improved compliance with TED regulations will in fact, reduce strandings to levels that, in conjunction with other protective measures, should further promote population recoveries for loggerhead and Kemp's ridley turtles.

The authors suggest that local, seasonal fisheries closures, concurrent with TED enforcement, could reduce strandings to even lower levels.



Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:

http://www.blackwell-synergy.com/doi/full/10.1046/j.1523-1739.2003.02057.x

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