Louise Brooks Foraging ecology of East Pacific green turtle (Chelonia mydas) in Bahia Magdalena, B.C.S., Mexico The purpose of this study is to examine the foraging ecology of juvenile green turtles found in Estero Banderitas, a tidal lagoon in Baja California Sur, Mexico. A long-term mark-recapture program is being used to characterize the population in this area. We are investigating the distribution and abundance of food items in the habitat, the diet and foraging behavior of turtles, and the diel movement and activity of sea turtles with respect to foraging and physical environmental factors such as tidal currents.

Research Mark-recapture studies in Estero Banderitas began in June 2000. These have continued year-round with the help of the School for Field Studies (www.fieldstudies.org) and the Grupo Tortuguero de las Californias. Our results indicate there is a year-round population of predominantly juvenile turtles in this area. We have captured both green and, to a lesser extent, hawksbill (Eretmochelys imbricata) turtles in Estero Banderitas. An algal survey will describe the benthic and drift algae in the area, and thus the distribution and abundance of available food items for green turtles. Gastric lavage will be used to investigate the diet of green turtles. Similarity and electivity of diet items will be assessed. We use GPS-VHF telemetry to investigate fine-scale, diel movement of turtles. Currently, we are designing an archival GPS-VHF tag that will float on the surface of the water at the end of a tether. Past telemetry results indicate that turtle movement is influenced by the strong tidal currents encountered in Estero Banderitas. Turtles frequently travel over 30 km per day. Foraging location may be dependent on tidal displacement. We are using an Acoustic Doppler Current Profiler to quantify the velocity and direction of tidal currents for comparison to turtle movements. This project relies on the assistance of members of the local community. Julio, Bediel, Joel and Juan, seen stacking a net, are members of the Grupo Tortuguero de las Californias. They have provided invaluable knowledge and dedication to the project. East Pacific green turtle (Chelonia mydas) 2002 version of tether tag with VHF transmitter Estero Banderitas The Bahía Magdalena-Almejas complex is one of the largest Pacific coastal lagoon systems in Mexico, and encompasses an area of greater than 1000 km2. Estero Banderitas (24°50’ – 25°00’ N and 112°05’ – 112°08’ W) is an evaporative basin located in the northern zone of Bahía Magdalena. The roughly 42 km2 estero is the largest in the complex, and is heavily influenced by tidal currents, with salinity and temperature increasing near the head of the basin. It is lined by red, white and black mangroves, is frequented by a diverse array of shorebirds, and is a nursery ground to gray whales. The view from our camp, showing typical Estero Banderitas habitat. The eastern Pacific population of green turtles is currently listed as endangered by the World Conservation Union. Estero Banderitas has been identified as an important feeding and developmental area for East Pacific green turtles. Protection of foraging habitat is clearly one of the most important aspects of conservation of Baja’s sea turtles because low survival in these habitats is one of the greatest threats to this population. This project is working with two non-profit organizations, Pronatura (www.pronaturanw.org) and Wildcoast (www.wildcoast.net), to establish Estero Banderitas as a sea turtle reserve. It has recently been recognized as one of four sites of great ecological importance in the Baja California to Bering Sea Marine Conservation initiative, which is led by the North American Fund for Environmental Cooperation. This project aims to advance the reserve effort by providing relevant data on sea turtle use of the area. At the same time, local involvement in the project provides imperative community support that will be needed to ensure the establishment of a successful, working reserve. 10,000 – 35,000 sea turtles are taken each year in the Baja California region. This shows just a fraction, collected over a few years from the dumps and beaches around Bahía Magdalena. The carapaces are from consumed turtles; the turtle in the foreground was probably drowned in a net. More information: School for Field Studies: http://www.fieldstudies.org/pages/programs/mexico.html The School for Field Studies has a Center for Coastal Studies in Puerto San Carlos, the largest town in the area. They have semester and summer semester programs for high school and college students, and they have a sea turtle program that partners with this project. Check out their website for more information. Many thanks to Terri Garland (trtletears@aol.com) for the countless hours of field assistance, support and garlic chopping, and for the photos on this page. Don’t lift them: she’ll come after you. But she can be contacted for access to these photos, and many more beauties. Maintained by: Elijah Woolery Office of the Webmaster Comments: webmaster@mlml.calstate.edu Last revision: February 20, 2003 URL, this page: http://www.mlml.calstate.edu/groups/bird_mam/lbrooks.htm