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Nesting success of Kemp's ridley sea turtles, Lepidochelys kempi, at Rancho Nuevo, Tamaulipas, Mexico, 1982-2004.

Article Excerpt
Introduction

The Kemp's ridley sea turtle, Lepidochelys kempi (Fig. 1) is the most endangered sea turtle in the world with a dramatic decline attributed to egg exploitation and incidental capture in commercial shrimp trawls (NRC, 1990). Its population had been declining at an alarming rate since at least 1947, when an amateur filmmaker revealed an estimated 40,000 female Kemp's ridleys nesting on the beach in a single day (Carr, 1963).

This species is unusual and endangered because 1) it nests primarily on a single stretch of beach with it's epicenter at Rancho Nuevo, Tamaulipas, Mexico, (Fig. 2), 2) it nests primarily during the daytime and often in large aggregations called arribadas (Fig. 3), which makes it easier for egg collectors, and 3) the Kemp's ridley also has a coastal distribution that makes it particularly vulnerable to incidental capture in commercial fishing trawls.

Massive egg exploitation on the beach during the 1940's and 1950's severely curtailed recruitment of new turtles into the population, and, combined with an increasing mortality of adult and subadult turtles in commercial fishing trawls starting in the early 1960's, the population was dealt a devastating blow and reduced to a total of 706 nests by 1985 (Burchfield and Foley (1)). A description and review of the shrimp trawl mortality on sea turtles is presented by the NRC (1990). NOAA's National Marine Fisheries Service (NMFS) addressed the problem of incidental turtle bycatch (Fig. 4, 5) with the development of turtle excluder devices (TED's) to reduce incidental mortality of turtles in commercial fishing trawls. A TED is basically a mesh grid inserted in a trawl that expels turtles from the net through a trap door (Fig. 6). A comprehensive review of TED development is provided by Watson et al. (1986).

In 1966, the Mexican Government (Instituto Nacional de Pesca) initiated a Kemp's ridley recovery program and began a research and conservation program near Rancho Nuevo. These efforts have concentrated on nest protection and increased hatchling production. In 1978, a collaborative program between Mexico and the United States (U.S. Fish and Wildlife Service) was developed to restore this species' population to a self sustainable level with the conservation efforts centered at Rancho Nuevo. Because this is the only place in the world where the large Kemp's ridley nesting aggregations occurred, it was declared the first National Reserve for the Management and Conservation of Sea Turtles in Mexico on 4 July 1977, when 13.2 miles (21.3 km) of beach were set aside (3.2 miles (5.1 km) north to 10 miles (16.2 km) south of Barra Coma). The Rancho Nuevo sanctuary was further expanded 10.6 miles (17 km) to the north (Barra Carrizo) in 2005. In 1981, the U.S. Fish and Wildlife Service contracted with the Gladys Porter Zoo in Brownsville, Tex., to administer the United States' field portion of the joint Mexico/U.S. effort to protect and increase the production of Kemp's ridley sea turtles at their natal beaches in the State of Tamaulipas, Mexico.

It is probable that the Kemp's ridley historically nested along...

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