The Interplay of Homing and Dispersal in Green Turtles: A Focus on the Southwestern Atlantic

Abstract

Current understanding of spatial ecology is insufficient in many threatened marine species, failing to provide a solid basis for conservation and management. To address this issue for globally endangered green turtles, we investigated their population distribution by sequencing a mitochondrial control region segment from the Rocas Atoll courtship area (n = 30 males) and four feeding grounds (FGs) in Brazil (n = 397), and compared our findings to published data (n (nesting) = 1205; n (feeding) = 1587). At Rocas Atoll, the first Atlantic courtship area sequenced to date, we found males were differentiated from local juveniles but not from nesting females. In combination with tag data, this indicates possible male philopatry. The most common haplotypes detected at the study sites were CMA-08 and CMA-05, and significant temporal variation was not revealed. Although feeding grounds were differentiated overall, intra-regional structure was less pronounced. Ascension was the primary natal source of the study FGs, with Surinam and Trindade as secondary sources. The study clarified the primary connectivity between Trindade and Brazil. Possible linkages to African populations were considered, but there was insufficient resolution to conclusively determine this connection. The distribution of FG haplotype lineages was nonrandom and indicative of regional clustering. The study investigated impacts of population size, geographic distance, ocean currents, and juvenile natal homing on connectivity, addressed calls for increased genetic sampling in the southwestern Atlantic, and provided data important for conservation of globally endangered green turtles.

Finding the ‘lost years’ in green turtles: insights from ocean circulation models and genetic analysis

“…Genetic surveys of southwestern Indian Ocean rookeries revealed patterns consistent with limited migration between the Atlantic and Indian basins [25,26], lending support to our findings. Mixing of diverse genetic stocks has also been documented in FGs where older turtles occur [10,13,27]. Thus, evidence increasingly suggests that the management of many turtle populations will require a broad approach across life-stages and regions [6,13].…”

“…Additionally, the juveniles sampled at FGs may be considerably older than five years and have, presumably, shifted from behaviour that promotes dispersal via ocean currents to 'homing'. Turtles from the Suriname rookery, where particle and MSA results were not well correlated, are known to forage in northeastern Brazil [10,27,31]. These FGs are counter to predominant currents and transport there is probably achieved by older turtles swimming through coastal waters.…”

“…We determined whether results from particle tracking simulations were correlated with m2m MSA estimates from Naro-Maciel et al [10] (i.e. 13 rookeries and 13 juvenile FGs).…”

“…We compared our modelling results to estimates from published genetic mixed-stock analyses (MSAs) [10][11][12]. The 'many-to-many' (m2m) MSA method, an extension of the original 'one-to-many' (o2m) MSA, uniquely incorporates metapopulation structure of multiple FGs and rookeries through two approaches that correspond to the two particle tracking techniques described earlier [11][12][13].…”

Predicting connectivity of green turtles at Palmyra Atoll, central Pacific: a focus on mtDNA and dispersal modelling

“…Four MSAs were carried out. The first (MSA 1 ) had equal prior probabilities for each region, whereas, in the second (MSA 2 ), priors were weighted to reflect annual numbers of nesting females [39,47] as shown in table 1. Following Proietti et al [55], in MSA 3 , priors were weighted according to particle drift trajectories intersecting with each RMU (the percentage of particles arriving at the PANWR from each RMU), and in Figure 1.…”