Abstract
For many marine species, locations of key foraging areas are not well defined. We used satellite telemetry and switching state-space modeling (SSM) to identify distinct foraging areas used by Kemp's ridley turtles (Lepidochelys kempii) tagged after nesting during 1998–2011 at Padre Island National Seashore, Texas, USA (PAIS; N = 22), and Rancho Nuevo, Tamaulipas, Mexico (RN; N = 9). Overall, turtles traveled a mean distance of 793.1 km (±347.8 SD) to foraging sites, where 24 of 31 turtles showed foraging area fidelity (FAF) over time (N = 22 in USA, N = 2 in Mexico). Multiple turtles foraged along their migratory route, prior to arrival at their “final” foraging sites. We identified new foraging “hotspots” where adult female Kemp's ridley turtles spent 44% of their time during tracking (i.e., 2641/6009 tracking days in foraging mode). Nearshore Gulf of Mexico waters served as foraging habitat for all turtles tracked in this study; final foraging sites were located in water <68 m deep and a mean distance of 33.2 km (±25.3 SD) from the nearest mainland coast. Distance to release site, distance to mainland shore, annual mean sea surface temperature, bathymetry, and net primary production were significant predictors of sites where turtles spent large numbers of days in foraging mode. Spatial similarity of particular foraging sites selected by different turtles over the 13-year tracking period indicates that these areas represent critical foraging habitat, particularly in waters off Louisiana. Furthermore, the wide distribution of foraging sites indicates that a foraging corridor exists for Kemp's ridleys in the Gulf. Our results highlight the need for further study of environmental and bathymetric components of foraging sites and prey resources contained therein, as well as international cooperation to protect essential at-sea foraging habitats for this imperiled species.
Highlights
Foraging resources are critical to sustain an individual’s survival, and represent an important component of an animal’s fitness (Krebs and Davies 1993)
Through analysis of the largest and longest-term satellitetracking data set for the species, we demonstrated the importance of nearshore Gulf of Mexico waters as foraging habitat for postnesting Kemp’s ridleys; we suggest that critical foraging habitat exists for the species in the northern Gulf of Mexico, off Louisiana, to which turtles show fidelity over time
Concentration of core-use foraging areas for turtles tracked from both RN and PAIS supports our assertion and underscores the importance of this habitat for these imperiled marine turtles
Summary
Foraging resources are critical to sustain an individual’s survival, and represent an important component of an animal’s fitness (Krebs and Davies 1993). Foraging optimality models suggest that animals will select resources of higher quality over those of lower quality, often resulting in optimal use of a patchy environment (MacArthur and Pianka 1966). Despite decades of study on foraging site selection in laboratories (Greenberg 1984) and the terrestrial environment (Bechard 1982), our understanding of the mechanisms of foraging site selection for marine species is limited (Bjorndal 1997). Attempts to confirm foraging behavior for sperm whales, for example, are usually short in duration and few in number due to logistical constraints (see Watwood et al 2006), and large-scale marine habitat surveys may provide information on abundance but not necessarily confirm foraging behavior (see Davis and Faragion 1998).
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