Immature East Pacific Green Turtles (Chelonia mydas) Use Multiple Foraging Areas off the Pacific Coast of Baja California Sur, Mexico: First Evidence from Mark-Recapture Data

Since 2001, Grupo Tortuguero has been conducting monthly inwater monitoring of East Pacific green turtles (Chelonia mydas), also known as black turtles, at four neritic foraging areas (Bahı́a Magdalena, Laguna San Ignacio, Punta Abreojos, Laguna Ojo de Liebre) along the Pacific coast of Baja California Sur, Mexico. Extensive tagging (883 turtles tagged of 1,183 turtles captured) and recaptures (154 tagged turtles recaptured at least once) at these four areas suggest that immature East Pacific green turtles show strong site fidelity to their neritic foraging grounds. However, in 2007, we recaptured two immature turtles, one in Laguna San Ignacio and the other in Bahı́a Magdalena, that were both originally captured in Punta Abreojos. To our knowledge, this represents the first direct evidence of immature East Pacific green turtles using multiple foraging areas along the Baja California Peninsula. This report highlights the importance of long-term monitoring efforts that encompass several habitats on a relatively large spatial scale (@80 km between Punta Abreojos and Laguna San Ignacio and @300 km between Punta Abreojos and Bahı́a Magdalena) to better understand the movements and habitat use of immature East Pacific green turtles on their neritic foraging areas. The East Pacific green turtle (Chelonia mydas) is currently listed as endangered in the World Conservation Union (IUCN) Red List (Hilton-Taylor 2000, Seminoff 2004). This subpopulation is frequently referred to as the black turtle due to morphological and color variations (Nichols 2003). East Pacific green turtles are highly migratory (Nichols 2003) and utilize several different habitats at different life stages (Seminoff et al. 2002a, Seminoff and Jones 2006, Koch et al. 2007). Green turtles from the Baja California Peninsula originate at Mexican rookeries located hundreds to thousands of kilometers south in the state of Michoacán and the Revillagigedos Archipelago, Tres Marias Islands, and perhaps even, to a lesser extent, from the Galápagos and Hawaiian islands (Márquez 1990, Nichols 2003, Koch et al. 2007). After hatching, it is assumed that green turtles immediately enter an oceanic stage for approximately 3–5 yr before recruiting to neritic foraging areas and undergoing a rapid ontogenetic diet shift (Balazs et al. 1987, Carr 1987, Bjorndal and Bolten 1997, Bolten 2003, Reich et al. 2007). Pacific Science (2010), vol. 64, no. 1:125–130 doi: 10.2984/64.1.125 : 2010 by University of Hawai‘i Press All rights reserved 1 This research was supported by Grupo Tortuguero, School for Field Studies–Center for Coastal Studies and Earthwatch Institute. Major funding for the ongoing Grupo Tortuguero sea turtle monitoring program has been provided by the National Marine Fisheries Service and the National Fish and Wildlife Foundation. Manuscript accepted 1 April 2009. 2 Florida Cooperative Fish and Wildlife Research Unit and Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, Florida 32611. 3 Archie Carr Center for Sea Turtle Research and Department of Biology, University of Florida, Gainesville, Florida 32611. 4 Grupo Tortuguero, La Paz, Baja California Sur, Mexico. 5 Universidad Autónoma de Baja California Sur, Departamento de Biologı́a Marina, La Paz, Baja California Sur, Mexico. 6 Ocean Revolution, Davenport, CA. 7 Department of Herpetology, California Academy of Sciences, San Francisco, California. 8 Both authors contributed equally. 9 Corresponding author (e-mail: [email protected]). Neritic foraging areas are arguably the most important habitat in the life cycle of an East Pacific green turtle (Nichols 2003). Juveniles may spend 20 yr or more in these developmental areas feeding on sea grasses and algae until they reach maturity (Seminoff et al. 2002b, Koch et al. 2007). These areas are also used by mature turtles between nesting cycles (Seminoff et al. 2002b, Nichols 2003). Although the presence of green turtles in neritic foraging areas along the Baja California Peninsula is well documented (Nichols 2003, Seminoff et al. 2003, Koch et al. 2006, 2007), long-term habitat use and connectivity among these sites remains unknown. Multiple recaptures indicate that immature East Pacific green turtles may spend several years in the same foraging area and that these turtles show strong site fidelity to the foraging area to which they originally recruited (Koch et al. 2007). To date, there have been no reported movements of tagged East Pacific green turtles between foraging areas (M.C.L.-C., V.K., A. Mariscal-Loza, and W.J.N., unpubl. data). Consequently, conservation and management plans have been designed accordingly. materials and methods Between 2001 and 2006 Grupo Tortuguero conducted in-water monitoring of sea turtles at four neritic foraging areas along the Pacific coast (24 15 0–27 48 0 N and 111 30 0–114 08 0 W) of Baja California Sur, Mexico. Study sites were located in Bahı́a Magdalena (BMA), Laguna San Ignacio (LSI), Punta Abreojos (PAO), and Laguna Ojo de Liebre (LOL) (Figure 1). These sites are important coastal foraging areas for East Pacific green turtles (Nichols 2003, Koch et al. 2006, 2007). Since 2001, East Pacific green turtles have been captured once per month along the shallow perimeter of each monitoring site using nylon and cotton entanglement nets (100 m long, 50 cm stretched mesh size). Captured turtles were able to surface and breathe because the nets contain little weight on the lead line. We set nets at slack tide during both day and night periods for approximately 10–24 hr and monitored them regularly (a1 hr) for entangled turtles. Upon capture, turtles were immediately removed from the nets and measured, weighed, and tagged at the closest landing. For each turtle, we recorded straight carapace length (SCL,G0.1 cm) from the nuchal notch to the longest posterior portion of the rear marginal scutes using a metal forester’s caliper. We determined mass to the nearest pound using a 100 lb (45.4 kg) springbalanced scale and then converted the measurement to kilograms. All captured turtles were tagged using metal tags (Inconel, National Band and Tag Company, Newport, Kentucky), applied proximal and adjacent to the first large scale on each rear flipper following Balazs (1999). A total of 883 turtles, out of 1,183 captured, was tagged from August 2001 to July 2006, and of these, 154 turtles have been recaptured at least once. Here we report on recaptures that were found at new foraging areas.