How many came home? Evaluating ex situ conservation of green turtles in the Cayman Islands

Abstract

Ex situ management is an important conservation tool that allows the preservation of biological diversity outside natural habitats while supporting survival in the wild. Captive breeding followed by re‐introduction is a possible approach for endangered species conservation and preservation of genetic variability. The Cayman Turtle Centre Ltd was established in 1968 to market green turtle (Chelonia mydas) meat and other products and replenish wild populations, thought to be locally extirpated, through captive breeding. We evaluated the effects of this re‐introduction programmme using molecular markers (13 microsatellites, 800‐bp D‐loop and simple tandem repeat mitochondrial DNA sequences) from captive breeders (N = 257) and wild nesting females (N = 57) (sampling period: 2013–2015). We divided the captive breeders into three groups: founders (from the original stock), and then two subdivisions of F1 individuals corresponding to two different management strategies, cohort 1995 (“C1995”) and multicohort F1 (“MCF1”). Loss of genetic variability and increased relatedness was observed in the captive stock over time. We found no significant differences in diversity among captive and wild groups, and similar or higher levels of haplotype variability when compared to other natural populations. Using parentage and sibship assignment, we determined that 90% of the wild individuals were related to the captive stock. Our results suggest a strong impact of the re‐introduction programmme on the present recovery of the wild green turtle population nesting in the Cayman Islands. Moreover, genetic relatedness analyses of captive populations are necessary to improve future management actions to maintain genetic diversity in the long term and avoid inbreeding depression.

Population recovery changes population composition at a major southern Caribbean juvenile developmental habitat for the green turtle, Chelonia mydas

“…However, the elevated genetic divergence could be due to sampling variance and smaller sample sizes (Table S3).

Figure 1Common Atlantic mtDNA haplotype proportions (CM-A01, CM-A03, CM-A05 and CM-A08; remaining haplotypes pooled under ‘Other’) in Lac Bay, Bonaire (BO; diamond) in 2006–2007 and 2015–2016 for <75.0 cm SCL juveniles (bottom-left insert ( A )) and <50.0 cm SCL juveniles (bottom-left insert ( B )) and in north-western (NW; triangles), south-western (SW; square), eastern (EA; circles) Caribbean and southern Atlantic (SA; crosses) green turtle rookeries: Aves Island, Venezuela (AV) 47,70 ; Buck Island, St. Croix, US Virgin Islands (BI) 47 ; Cayman Islands (CI) 74 ; Cuba (CU) 71 ; Tortuguero, Costa Rica (CR) 40,70 ; Central Eastern Florida, USA (EF) 72 ; French Guiana (FG) 73 ; Guadeloupe (GU) 73 , Quintana Roo, Mexico (MX) 70 ; South Florida, USA (SF) 72 ; Suriname (SU) 47,70,73 ; Rocas Atoll, Brazil (RA) 70,76 ; Fernando de Noronha, Brazil (FN) 76 ; Trindade Island, Brazil (TI) 76 ; Ascension Island, UK (AI) 70,75,79 ; Poilão, Guinea Bissau (GB) 70,75,77 ; São Tomé and Príncipe (ST) 75 ; Bioko Island, Equatorial Guinea (BIO) 75 .

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Precise natal homing and an estimate of age at sexual maturity in hawksbill turtles

“…Identifying genealogical relationships (i.e. kinship) among individuals has been instrumental in understanding important ecological questions of wild populations (Avise, 2004), such as mating systems (Griffith, Owens & Thurman, 2002; Vigilant et al ., 2015), dispersal (Arora et al ., 2012; Feldheim et al ., 2014; Salles et al ., 2016; Warner, Willis & van Oppen, 2016; Baetscher et al ., 2019), heritability (Dubuc et al ., 2014) and links to captive breeding and reintroduction programs (Barbanti et al ., 2019). Aside from observing parent–offspring interactions, kin relationships are typically unknown in wild populations but can be estimated by calculating the proportion of shared genetic material (identity by descent) between individuals (Blouin, 2003).…”

Cayman Islands Sea Turtle Nesting Population Increases Over 22 Years of Monitoring

“…While nesting numbers have increased dramatically for these two species, it is important to consider this modern-day population increase in the context of historical levels of abundance in the 1600s, when the nesting turtle population in the Cayman Islands was estimated to be more than 2.5 million (Jackson, 1997). Today, the green turtle nesting population has been estimated at around 100-150 females (Barbanti et al, 2019) and nesting data suggests there are even fewer loggerheads turtles. Additionally, these populations are still experiencing several anthropogenic threats including illegal take of adult turtles and the impact of artificial lighting causing hatchling mortality.…”

“…Through documentation of permanent marks known as "living tags, " the first farm-released green turtles were recorded nesting on Grand Cayman beaches in 2002, at an age of 15 years (1 individual) and 17 years (2 individuals) (Bell et al, 2005). A genetic study determined that 90% of wild nesting green turtles (n = 57) in Grand Cayman in 2013/2014 were related as either offspring or full or half-siblings to the turtle farm individuals (Barbanti et al, 2019) and our study showed that the majority of green turtle nesting occurs in close proximity to the Cayman Turtle Farm breeding location. Therefore, the increase in nest numbers detected in the early years of nest monitoring may have been driven by the turtles released from the Cayman Turtle Farm in the 1980s reaching maturity after more than two decades in the wild.…”

“…It is essential that re-introduction programmes have pre-determined goals and careful consideration of benefits and risks and undertake robust monitoring and reporting (Bennett et al, 2017). Evaluation of the effectiveness of an ex-situ breeding programme as a conservation tool must take into account the genetic diversity of the founder stock and the re-established population (Barbanti et al, 2019), and the effect on wild populations must also be evaluated to determine whether these efforts are worth the associated costs (D'Cruze et al, 2015). In Grand Cayman, from more than 25,000 yearling and hatchling turtles released between 1980 and 1989 (Bell et al, 2005), the green turtle nesting population is now estimated at 100-150 adult females (Barbanti et al, 2019).…”