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

Abstract

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.

A New Approach to Mixed Stock Analysis that Informs on the Management and Conservation of Hawksbill in the Wider Caribbean: the Case of the Legal Fishery in Jardines del Rey, Cuba

“…The incorporation in the MSAs of the present study of other WC rookeries and aggregations recently characterized Gorham et al, 2014;Cazabon-Mannette et al, 2016) reinforces the contributions from the largest rookeries (ME, BaL and MI). These populations have experienced the highest recovery rates in decades (ca.…”

“…The importance of selecting the data in rookeries and aggregations as well as the assumptions to execute the MSA is more evident when our initial data are contrasted with these of other studies. For example, our approach excluded the cumulative haplotype frequencies in rookeries and aggregations as well as the Texas pelagic individuals from Gorham et al (2014)). This demonstrates that when the sampling or original data are robust the contributions will tend to the same result even if the a priori assumptions vary somewhat.…”

Juvenile hawksbill residency and habitat use within a Caribbean marine protected area

“…In some areas, such as along the south forereef, where receivers fringe both high rugosity reef and low-lying sea grass pastures/sand, the raster cell size may have been too coarse to capture the microhabitat detail. Juvenile hawksbills have been observed using fringe habitats, similar in composition to those encapsulated within our low-rugosity sand and high-rugosity reef categories, to forage for food and rest in the nearby safety provided by the rugose reef structure (Bjorndal & Bolten 2010, Gorham et al 2014. Regardless of the particular microhabitat, hawksbills in this study did select these fringe areas at night (Fig.…”

Hawksbill sea turtle life-stage durations, somatic growth patterns, and age at maturation

“…In fact, in Flo rida, hawksbills regularly occur in nearshore waters off the southeastern coast, in the Florida Keys (in clu ding the Marquesas and Dry Tortugas) and in GoM waters off the west-central coast; however, they are rarely encountered along the upper northwest coast or in northeastern Florida (reviewed by Meylan & Red low 2006). In-water survey, power plant entrapment, museum, cold-stunning, and incidental capture records in Florida have documented the regular presence of juvenile and, in some cases, adult-sized hawksbills (Meylan & Redlow 2006, Eaton et al 2008, Hart et al 2013, Wood et al 2013, Gorham et al 2014, Herren et al 2018. Individuals in several foraging areas in Florida as well as the US Virgin Is lands have also exhibited site fidelity and ex tended residency over periods of more than 1 yr (Hart et al 2012, Wood et al 2013, Gorham et al 2014, Herren et al 2018.…”