Foraging area fidelity for Kemp's ridleys in the Gulf of Mexico

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.

Bahamas connection: residence areas selected by breeding female loggerheads tagged in Dry Tortugas National Park, USA

“…The model was described in 2005 [41] and has previously been applied to the movement of marine animals including turtles [1,3,4,42,43,[46][47][48][49][50]56,80]. Location data obtained through satellite transmitters are often received at irregular time intervals and sometimes involve large gaps and positional errors.…”

“…Defining these areas can be challenging in the marine environment given their often separate geographic locations, but electronic tags (i.e., satellite, GPS, and geolocation tags) have allowed delineation of high-use at-sea residence sites for marine megafauna, including sea turtles [1][2][3][4][5][6]. Hamann et al [5] ranked efforts to define important in-water habitats as one of the top priorities worldwide for imperiled marine turtles.…”

“…Connections between rookeries and foraging grounds are only now being quantified [2][3][4]11,12]. Loggerhead sea turtles nest every 2-5 years, depositing 2-6 clutches of 75-120 eggs approximately every 2 weeks during the nesting season [13][14][15][16][17][18].…”

“…SSM has been used to identify locations when turtles show directed movements versus area-restricted search (ARS) patterns-deemed previously as migration and inter-nesting or foraging 'modes' [1,3,4,[40][41][42][43][44][45][46][47][48][49][50]. When combined with MCP (simple polygon created with home-range locations [51,52]) or KDE (a nonparametric method used to identify one or more areas of disproportionately heavy use [i.e.…”

“…core areas] within a home-range boundary, see [53][54][55]), SSM has been suggested as a way to enhance analysis of Argos tracking data sets [56]. SSM was recently used to delineate foraging zones for post-nesting Kemp's ridleys in the GoM [4], define the migrations and foraging areas for leatherback turtles nesting in the Pacific Ocean [47,57], determine foraging areas for juvenile green turtles in the SW Atlantic [58], and describe residence or foraging areas in the GoM for female loggerheads from three separate subpopulations [3].…”