Hawksbill Sea Turtles (Eretmochelys imbricata) are listed as a critically endangered species due to low population numbers worldwide. For species like this, adequate monitoring and assessments of the size structure of populations are essential. Sea turtle capture methods, including the type of fishing gear, vary widely, causing biases in the size structure of the captured individuals and hindering comparisons between studies and populations. We analyzed the effect of heterogeneity in capture methods and the statistical treatment of data across four studies of these turtles in the Gulf of California, Mexico. Normality tests indicated that only two datasets had normal distributions. Modal groups were closely associated with the gear and methods employed. Studies with the smallest size classes encompassed individuals captured by free-diving; intermediate size classes involved the use of nets and combined methods (gillnets with 25-and 50-cm stretched mesh size checked at regular intervals, strike-netting, stranded carcasses), while studies with the largest size classes were caught using gillnets (50-cm stretched mesh) and strike-netting. The frequency distribution of the life stages (juveniles, subadults, adults) varied considerably across studies, with juveniles ranging from 37-100% and subadults from 0-56% of the total numbers. Given the challenges of standardizing methods (whose use and effectiveness depend on local conditions), we recommend that explicit capture details be reported for each individual, morphometric variables be homogenized, and a priori statistical tests be performed to guide the choice of appropriate analyses.
Accurate population estimates are fundamental for assessing the conservation status of endangered species and guiding management actions. The Utila Spiny-tailed Iguana (Ctenosaura bakeri) is a Critically Endangered species on the Red List of the International Union for Conservation of Nature, endemic to Utila, Honduras, and one of the few reptiles specialized for mangrove ecosystems. Despite its conservation importance, reliable population estimates remain limited due to its cryptic behavior and restricted distribution. We evaluated two survey approaches, Mark-recapture and Distance Sampling, across eight mangrove sites between March and October 2024 to estimate population size and describe demographic structure. Observations were strongly adult-biased and revealed an overall balanced sex ratio (0.82 males per one female), with male-biased ratios detected at several urban-associated sites. Of 71 marked adults, only 18 were recaptured (25.35%), preventing robust mark-recapture population estimation. In contrast, distance sampling, based on 448 detections, yielded site-specific density estimates ranging from 6.33 to 32.07 individuals/ha, with lower densities observed in disturbed mangrove areas. Extrapolated across 650 ha of mangrove habitat, we estimated that the island-wide population at 9,945 individuals (95% confidence interval = 7,176-13,812). Our results demonstrate that distance sampling provided a more reliable method for estimating population size in this species. The spatial variation in density highlights the influence of habitat degradation and underscores the urgent need to strengthen mangrove protection, mitigate hunting pressure, and implement continuous, standardized monitoring to ensure the persistence of C. bakeri on the island.
Fragmented landscapes can potentially disrupt biphasic amphibians that migrate between terrestrial californiense) is primarily relegated to preserves situated adjacent to properties fragmented by various anthropogenic land uses. We captured migrating adult SCTS using a pitfall trap array that encircled a breeding pool and identified individuals using spot pattern analysis. We assessed the movement and orientation of SCTS in relation to land uses within 100-m wide buffers ranging 100-500 m around the breeding pool. Our land use analyses included Cattle Grazed Preserve, Rural Mixed-Use, and Preserve lands. We found that many breeding SCTS used this pool, and we captured 585 individuals over 2 y. Individual SCTS moved nonrandomly at the pool with a weak tendency to move back toward the upland areas from which they originated. The spatial distribution of incoming SCTS capture rates differed significantly from outgoing capture rates. Adults entering from regions containing Rural Mixed-Use lands 200-500 m from the pool exited significantly farther from their points of entry, relative to those entering from Cattle Grazed Preserve and Preserve lands. In contrast, we found no detectable difference in orientation between Cattle Grazed Preserve and Preserve.
The island of St Barthelemy, part of the Anguilla Bank in the northern Lesser Antilles is one of the last strongholds for the Critically Endangered Lesser Antillean Iguana (Iguana delicatissima). The arrival of invasive alien iguanas (Iguana rhinolophus, L iguana) has resulted in hybridization, threatening the persistence of the endemic species. We present a long-term assessment of two L delicatissima populations (consisting of 14 individuals: 5 males, 9 females for each population) translocated in 2011 from St Barthelemy to the satellite islets of Fourchue and Fregate, 10-11 y post-translocation. We analyzed partial sequences of the nuclear Cmos gene, the mitochondrial ND4 gene, and 10 microsatellite loci to evaluate genetic diversity and founder effects. Our results demonstrate that each founder population is genetically distinct and lacks the full genetic variability of the source population. Genetic drift in the two descendant populations likely precipitated the loss of specific Cmos and ND4 haplotypes and reduced microsatellite polymorphism. The relict population on filet Fourchue retained a unique polymorphism, and one individual captured in 2022 was homozygous for a Cmos haplotype characteristic of I. rhinolophus. Furthermore, iguanas on Fregate, which was unoccupied prior to translocation, exhibited Cmos and ND4 haplotypes absent from the original founders, indicating potential inter-islet dispersal. Across the three populations (St Barthelemy, Fourchue, Fregate), four novel Cmos and 11 novel ND4 haplotypes were identified. We recommend continued genetic monitoring, prevention of invasive alien iguana arrivals, removal of hybrids, and management of these small, interconnected populations as a metapopulation.
Quantitative data about animal populations are essential for developing monitoring and conservation strategies. Occupancy estimation is a useful tool for monitoring species that are difficult to detect (e.g., many amphibian species) and to assess how environmental variables affect species distributions. We evaluated how the environmental characteristics of a conserved tropical forest in southern Mexico affect the occupancy and Robber Frog (Craugastor berkenbuschii), and Vaillant's Frog (Lithobates vaillanti). We initially estimated two parameters, occupancy and detection probabilities of these anuran species, and subsequently we evaluated how several environmental variables affect both parameters. We sampled the three species in 40 plots at two sites in Santa Maria Chimalapa, Oaxaca, southern Mexico, and we fitted species-specific single-season occupancy models. Craugastor berkenbuschii had the highest estimated occupancy (0.82), followed by L. vaillanti (0.66) and D. chamulae (0.25). We observed positive relationships of D. chamulae occupancy and detectability with elevation and temperature, respectively. Additionally, we found a positive relationship between C. berkenbuschii detectability and relative humidity, and we observed negative relationships between the occupancy of both C. berkenbuschii and L. vaillanti and the number of trees in the plots. Our study provides insight into how these three anuran species respond to habitat conditions and provides a baseline for future long-term research focused on species that inhabit preserved tropical forests.
