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Monitoring green turtles (Chelonia mydas) at a coastal foraging area in Baja California, Mexico: multiple indices to describe population status

Published online by Cambridge University Press:  08 January 2004

Jeffrey A. Seminoff
Affiliation:
Archie Carr Center for Sea Turtle Research and Department of Zoology, University of Florida, Gainesville, Florida 32611-8525, USA
T. Todd Jones
Affiliation:
The Animal Care Center, Department of Zoology, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
Antonio Resendiz
Affiliation:
Instituto Nacional de Ecología, Dirección General de Vida Silvestre, Secretaria de Medio Ambiente y Recursos Naturales, Ensenada, Baja California, México
Wallace J. Nichols
Affiliation:
Wildcoast International Conservation Team, PO Box 324, Davenport, California 95017, USA
Milani Y. Chaloupka
Affiliation:
School of Economics, University of Queensland, Brisbane, Queensland 4072, Australia

Abstract

From June 1995 to August 2002 we assessed green turtle (Chelonia mydas) population structure and survival, and identified human impacts at Bahía de los Angeles, a large bay that was once the site of the greatest sea turtle harvest rates in the Gulf of California, Mexico. Turtles were captured live with entanglement nets and mortality was quantified through stranding surveys and flipper tag recoveries. A total of 14,820 netting hours (617·5 d) resulted in 255 captures of 200 green turtles. Straight-carapace length and mass ranged from 46·0–100·0 cm (mean=74·3±0·7 cm) and 14·5–145·0 kg (mean=61·5±1·7 kg), respectively. The size–frequency distribution remained stable during all years and among all capture locations. Anthropogenic-derived injuries ranging from missing flippers to boat propeller scars were present in 4% of captured turtles. Remains of 18 turtles were found at dumpsites, nine stranded turtles were encountered in the study area, and flipper tags from seven turtles were recovered. Survival was estimated at 0·58 for juveniles and 0·97 for adults using a joint live-recapture and dead-recovery model (Burnham model). Low survival among juveniles, declining annual catch per unit effort, and the presence of butchered carcasses indicated human activities continue to impact green turtles at this foraging area.

Type
Research Article
Copyright
2003 Marine Biological Association of the United Kingdom

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