AQUATIC BIOLOGY Aquat Biol Vol. 9: 113–121, 2010 doi: 10.3354/ab00222 Published online April 15 INTRODUCTION Due to spatial variability in intensity of threats, track- ing movement is fundamental to the management of endangered animals (Cooke 2008, Bograd et al. 2010). As commercially valuable migratory species which often overlap in distribution with fisheries, marine turtles are susceptible to directed and incidental harvest through- out their range (Lewison et al. 2004). It is well established that impacts of fishery-related mortality cross geo- political boundaries; for example, green turtles originat- ing from both regionally important (Tortuguero, Costa Rica; Troëng et al. 2005) and critically reduced (Cayman Islands; Blumenthal et al. 2006) rookeries migrate to foraging grounds in Nicaragua, where a commercial turtle fishery persists (Campbell & Lagueux 2005). How- ever, in addition to tracking transboundary migrations, characterization of fine-scale movements (e.g. with re- spect to the boundaries of local marine protected areas) has key implications for marine turtle management, as has been demonstrated in adult loggerheads (Schofield et al. 2007, Zbinden et al. 2007). For juvenile green turtles, while individuals on foraging grounds are known to make daily movements from foraging to resting sites (Mendonca 1983, Ogden et al. 1983), few studies have investigated how local movements determine vulnera- bility to anthropogenic threats. Deployment of remote systems such as satellite transmitters (see Godley et al. 2008 for review) and light geolocation system tags (Storch 2003, Fuller et al. 2008) has been extremely effective in tracking long- range migrations of marine turtles, but location resolu- tion of these instruments is generally insufficient to characterize fine-scale patterns of movement of resi- © Inter-Research 2010 · www.int-res.com *Email: jblumenthal@seaturtle.org Life in (and out of) the lagoon: fine-scale movements of green turtles tracked using time-depth recorders J. M. Blumenthal 1, 2, * , T. J. Austin 1 , J. B. Bothwell 1 , A. C. Broderick 2 , G. Ebanks-Petrie 1 , J. R. Olynik 1 , M. F. Orr 1 , J. L. Solomon 1 , M. J. Witt 2 , B. J. Godley 2 1 Cayman Islands Department of Environment, Box 486, Grand Cayman KY1-1106, Cayman Islands 2 Centre for Ecology and Conservation, School of Biosciences, University of Exeter Cornwall Campus, Penryn TR10 9EZ, UK ABSTRACT: Tracking fine-scale movements in relation to threats is fundamental to the management of exploited marine species, yet there is considerable difficulty associated with gathering such data at sea. By combining a capture-recapture study with deployment of time-depth recorders (TDRs) and ultrasonic tags, we elucidated distribution and daily movements of juvenile green turtles Chelonia mydas exposed to a legal marine turtle fishery in the Cayman Islands. For instrumented turtles, dis- tinct diel activity patterns were observed: dives during the day were shorter and more active than those at night, implying diurnal foraging and nocturnal resting. Spatially, while capture and recap- ture locations suggested fidelity to a shallow lagoon, when turtles were fitted with TDRs and ultra- sonic tags we demonstrated that they regularly moved out of the lagoon and onto the reef, where they could legally be captured in the marine turtle fishery. Our results are thus novel and valuable in a management context in that we demonstrated that seemingly protected aggregations of juvenile green turtles within a lagoon were, in fact, exposed to legal capture on a near-daily basis. This emphasizes the importance of assessing diel activity patterns of juvenile marine turtles, particularly with respect to directed take and other threats. KEY WORDS: Green turtle · Chelonia mydas · Spatial ecology · Seagrass · Coral reef · Time-depth recorder · TDR Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESS