Long-term behavior at foraging sites of adult female loggerhead sea turtles (Caretta caretta) from three Florida rookeries

Abstract

We used satellite telemetry to study behavior at foraging sites of 40 adult female loggerhead sea turtles (Caretta caretta) from three Florida (USA) rookeries. Foraging sites were located in four countries (USA, Mexico, the Bahamas, and Cuba). We were able to determine home range for 32 of the loggerheads. One turtle moved through several temporary residence areas, but the rest had a primary residence area in which they spent all or most of their time (usually >11 months per year). Twenty-four had a primary residence area that was <500 km² (mean = 191). Seven had a primary residence area that was ≥500 km² (range = 573-1,907). Primary residence areas were mostly restricted to depths <100 m. Loggerheads appeared to favor areas with larger-grained sediment (gravel and rock) over areas with smaller-grained sediment (mud). Short-term departures from primary residence areas were either looping excursions, typically involving 1-2 weeks of continuous travel, or movement to a secondary residence area where turtles spent 25-45 days before returning to their primary residence area. Ten turtles had a secondary residence area, and six used it as an overwintering site. For those six turtles, the primary residence area was in shallow water (<17 m) in the northern half of the Gulf of Mexico (GOM), and overwintering sites were farther offshore or farther south. We documented long winter dive times (>4 h) for the first time in the GOM. Characterizing behaviors at foraging sites helps inform and assess loggerhead recovery efforts.

Fig. 1

Geographic centers of residence areas for 40 loggerheads outfitted with a platform transmitter terminal during 1998–2001 after nesting in Florida. The location of each nesting beach is denoted by a triangle and identified by a number. The location of each residence area is denoted by a circle with a number that corresponds to the nesting beach of that loggerhead. Some residence areas on the West Florida Shelf had more overlap than indicated (some circles were moved slightly to make them visible). The dotted line shows the shelf break (at 200 m)

Fig. 2

Loggerhead primary residence area as indicated by filtered positions and as described by a minimum convex polygon (MCP), an α-Hull (where α = 3), and a FKD of 90 and 50 %. This loggerhead was outfitted with a platform transmitter terminal on July 28, 2000, after nesting in western central Florida. a Spatial representation of the postnesting migration (open points, 14 days) and subsequent primary residence area (closed points, 237 days). b Extent of primary residence area as determined by an MCP (241 km²) and an α-Hull analysis (77 km²). c Extent of primary residence area as represented by an FKD of 90 % (99 km²) and 50 % (22 km²)

Fig. 3

The movements of a loggerhead on the west Florida continental shelf (WFS) after completing its postnesting migration. This turtle was outfitted with a platform transmitter terminal on July 14, 2001, after nesting in northwestern Florida. The triangle denotes the point at which the track begins (end of postnesting migration), and the circle denotes the point at which the tracking period ended. This loggerhead had several areas of temporary residence (1–3 months), while otherwise ranging over 28,000 km² of the southern portion of the WFS over a period of 214 days

Fig. 4

Examples of residence behavior at foraging sites of three loggerheads (turtles a–c). All three were outfitted with a platform transmitter terminal during August 1999 or August 2000 after nesting in central eastern Florida. Turtle a spent the entire tracking period (350 days) within the primary residence area; turtle b made a 12-day looping excursion from the primary residence area during a 393-day tracking period; and turtle c had a secondary residence area. Turtle c spent 211 days in the primary residence area (area to the southeast) and 30 days in the secondary residence area (area to the northwest)

Fig. 5

Evidence of a primary and secondary residence area in the dive data of a loggerhead with limited location data (a) and frequency of dive durations for this same turtle when in its primary and secondary residence areas (b). This turtle was outfitted with a platform transmitter terminal on July 10, 2000, after nesting in northwestern Florida. The residence areas were on the west Florida continental shelf. The dive data indicated that there was a shallower primary residence area and a deeper (20–40 m) secondary residence area that was used only during the winter (Dec–Feb)