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Alternate Title

Development of a Kemp's Ridley Sea Turtle Stock Assessment Model

Authors

Benny J. Gallaway, LGL Ecological Research Associates, Inc.
William J. Gazey, W.J. Gazey Research
Charles W. Caillouet Jr., Nonaffiliated Marine Fisheries Scientist
Pamela T. Plotkin, Texas Sea Grant College Program
F. Alberto Abreu Grobois, Universidad Nacional Autónoma de México
Anthony F. Amos, University of Texas at Austin
Patrick M. Burchfield, Gladys Porter Zoo
Ray R. Carthy, U.S. Geological Survey
Marco A. Castro Martínez, La Comisión Nacional de Áreas Naturales Protegidas
John G. Cole, LGL Ecological Research Associates, Inc.
Andrew T. Coleman, Institute for Marine Mammal Studies
Melissa Cook, National Marine Fisheries Service
Steven DiMarco, Texas A&M University
Sheryan P. Epperly, National Marine Fisheries Service
Masami Fujiwara, Texas A&M University
Daniel Gomez Gamez, Gladys Porter Zoo
Gary L. Graham, Texas Sea Grant College Program
Wade L. Griffin, Texas A&M University
Francisco Illescas Martínez, Gladys Porter Zoo
Margaret M. Lamont, U.S. Geological Survey
Rebecca L. Lewison, San Diego State University
Kenneth J. Lohmann, University of North Carolina
James M. Nance, National Marine Fisheries Service
Jonathan Pitchford, Institute for Marine Mammal Studies
Nathan F. Putman
Scott W. Raborn
Jeffrey K. Rester, Gulf States Marine Fisheries Commission
Jack J. Rudloe, Gulf Specimen Marine Laboratories, Inc.
Laura Sarti Martínez, La Comisión Nacional de Áreas Naturales Protegidas
Mark Schexnayder, Louisiana Department of Wildlife and Fisheries
Jeffrey R. Schmid, Conservancy of Southwest Florida
Donna J. Shaver, U.S. National Park Service
Christopher Slay, Coastwise Consulting, Inc.
Anton D. Tucker, Mote Marine Laboratory
Mandy Tumlin, Louisiana Department of Wildlife and Fisheries
Thane Wibbels, University of Alabama at Birmingham
Blanca M. Zapata Najera, La Comisión Nacional de Áreas Naturales Protegidas

Abstract

We developed a Kemp’s ridley (Lepidochelys kempii) stock assessment model to evaluate the relative contributions of conservation efforts and other factors toward this critically endangered species’ recovery. The Kemp’s ridley demographic model developed by the Turtle Expert Working Group (TEWG) in 1998 and 2000 and updated for the binational recovery plan in 2011 was modified for use as our base model. The TEWG model uses indices of the annual reproductive population (number of nests) and hatchling recruitment to predict future annual numbers of nests on the basis of a series of assumptions regarding age and maturity, remigration interval, sex ratios, nests per female, juvenile mortality, and a putative ‘‘turtle excluder device effect’’ multiplier starting in 1990. This multiplier was necessary to fit the number of nests observed in 1990 and later. We added the effects of shrimping effort directly, modified by habitat weightings, as a proxy for all sources of anthropogenic mortality. Additional data included in our model were incremental growth of Kemp’s ridleys marked and recaptured in the Gulf of Mexico, and the length frequency of stranded Kemp’s ridleys. We also added a 2010 mortality factor that was necessary to fit the number of nests for 2010 and later (2011 and 2012). Last, we used an empirical basis for estimating natural mortality, on the basis of a Lorenzen mortality curve and growth estimates. Although our model generated reasonable estimates of annual total turtle deaths attributable to shrimp trawling, as well as additional deaths due to undetermined anthropogenic causes in 2010, we were unable to provide a clear explanation for the observed increase in the number of stranded Kemp’s ridleys in recent years, and subsequent disruption of the species’ exponential growth since the 2009 nesting season. Our consensus is that expanded data collection at the nesting beaches is needed and of high priority, and that 2015 be targeted for the next stock assessment to evaluate the 2010 event using more recent nesting and in-water data.

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