Characterization of a Subtropical Hawksbill Sea Turtle (<i>Eretmocheyles imbricata</i>) Assemblage Utilizing Shallow Water Natural and Artificial Habitats in the Florida Keys

<div><p>In order to provide information to better inform management decisions and direct further research, vessel-based visual transects, snorkel transects, and in-water capture techniques were used to characterize hawksbill sea turtles in the shallow marine habitats of a Marine Protected Area (MPA), the Key West National Wildlife Refuge in the Florida Keys. Hawksbills were found in hardbottom and seagrass dominated habitats throughout the Refuge, and on man-made rubble structures in the Northwest Channel near Cottrell Key. Hawksbills captured (N = 82) were exclusively juveniles and subadults with a straight standard carapace length (SSCL) ranging from 21.4 to 69.0cm with a mean of 44.1 cm (SD = 10.8). Somatic growth rates were calculated from 15 recaptured turtles with periods at large ranging from 51 to 1188 days. Mean SSCL growth rate was 7.7 cm/year (SD = 4.6). Juvenile hawksbills (<50 cm SSCL) showed a significantly higher growth rate (9.2 cm/year, SD = 4.5, N = 11) than subadult hawksbills (50–70 cm SSCL, 3.6 cm/year, SD = 0.9, N = 4). Analysis of 740 base pair mitochondrial control region sequences from 50 sampled turtles yielded 12 haplotypes. Haplotype frequencies were significantly different compared to four other Caribbean juvenile foraging aggregations, including one off the Atlantic coast of Florida. Many-to-one mixed stock analysis indicated Mexico as the primary source of juveniles in the region and also suggested that the Refuge may serve as important developmental habitat for the Cuban nesting aggregation. Serum testosterone radioimmunoassay results from 33 individuals indicated a female biased sex ratio of 3.3 females: 1 male for hawksbills in the Refuge. This assemblage of hawksbills is near the northern limit of the species range, and is one of only two such assemblages described in the waters of the continental United States. Since this assemblage resides in an MPA with intensive human use, basic information on the assemblage is vital to resource managers charged with conservation and species protection in the MPA.</p></div

Straight standard carapace length (SSCL) size-class distribution of hawksbill turtles for all captures in the Key West National Wildlife Refuge, 2002–2011.

<p>Straight standard carapace length (SSCL) size-class distribution of hawksbill turtles for all captures in the Key West National Wildlife Refuge, 2002–2011.</p

Rookery contribution estimates for juvenile hawksbill turtles foraging in the KWNWR based on mixed stock analysis weighted by rookery size.

<p>Rookery source codes are explained in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114171#pone.0114171.s001" target="_blank">S1 Table</a>.</p

Location of the Key West National Wildlife Refuge, Monroe County, Florida.

<p>Location of the Key West National Wildlife Refuge, Monroe County, Florida.</p

Pairwise comparisons for 740 base pair control region haplotype frequencies for hawksbill turtle juvenile foraging aggregations in the Greater Caribbean region.

<p>Pairwise FST values are above the diagonal (all values significant for alpha  = 0.01). P-values for exact tests of differentiation are below the diagonal. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114171#pone.0114171.s001" target="_blank">S1 Table</a> for code explanations.</p><p>Pairwise comparisons for 740 base pair control region haplotype frequencies for hawksbill turtle juvenile foraging aggregations in the Greater Caribbean region.</p

Hawksbill turtle sighting locations in the western KWNWR, 2001–2011.

<p>Hawksbill turtle sighting locations in the western KWNWR, 2001–2011.</p

Growth in standard straight carapace length (SCL) for hawksbill turtles (n = 15) captured and recaptured within the KWNWR, 2002–2011.

<p>Plot A shows a linear fit to log transformed growth rates (R-squared  = 0.70, p<0.0001), and plot B shows mean growth rates (solid circles) and ranges (vertical lines) for hawksbills within size groupings. All sizes are means of initial and recapture SCL.</p

Hawksbill turtle sighting locations in the central KWNWR, 2001–2011.

<p>Hawksbill turtle sighting locations in the central KWNWR, 2001–2011.</p

Hawksbill turtle sighting locations in the northeast KWNWR, 2001–2011.

<p>Hawksbill turtle sighting locations in the northeast KWNWR, 2001–2011.</p