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Context The extinction risk of sharks and rays exceeds that of most other vertebrates. Genetic analyses can help identify conservation risks. Aims Identification of Fiji’s maskray and testing the null hypothesis of no genetic differentiation within the species over time. Methods Mitochondrial DNA cytochrome oxidase subunit 1 (COI) barcoding was used for species identification, and DArT-seq technology to monitor the genetic diversity. Cohort samples were collected in 2015 and 2022. A subset from each cohort was barcoded. The genetic survey was complemented by a size comparison between the two cohorts. Key results Barcoding of the COI gene showed a maximum similarity of 97.84% to Kuhl’s maskray (Neotrygon kuhlii) and 96.83% to the Coral Sea maskray (Neotrygon trigonoides), but no higher-level distinct species match to reference sequences in the Barcode of Life Datasystem. Genotyping of 56 individuals in two cohorts yielded 21,293 single nucleotide polymorphisms (SNPs), and 3871 SNPs per individual were retained. The neutral genetic diversity remained stable over time. The 2015 cohort showed positive inbreeding, with one full-sibling pair identified in each cohort. Body size comparisons indicated a significant reduction in disc length and width in the 2022 cohort. Conclusions The smaller body size of the 2022 cohort may hint at increased fishing pressure, but genetic diversity has not been affected. Thus, the null hypothesis is accepted. Implications These findings provide insights into the genetic diversity of Fiji’s maskray and enable a genetic comparison with current Neotrygon species known in the region. Taxonomy confirmation is needed, but the presence of a cryptic or potentially new maskray in Fiji seems plausible.
Context The extinction risk of sharks and rays exceeds that of most other vertebrates. Genetic analyses can help identify conservation risks. Aims Identification of Fiji’s maskray and testing the null hypothesis of no genetic differentiation within the species over time. Methods Mitochondrial DNA cytochrome oxidase subunit 1 (COI) barcoding was used for species identification, and DArT-seq technology to monitor the genetic diversity. Cohort samples were collected in 2015 and 2022. A subset from each cohort was barcoded. The genetic survey was complemented by a size comparison between the two cohorts. Key results Barcoding of the COI gene showed a maximum similarity of 97.84% to Kuhl’s maskray (Neotrygon kuhlii) and 96.83% to the Coral Sea maskray (Neotrygon trigonoides), but no higher-level distinct species match to reference sequences in the Barcode of Life Datasystem. Genotyping of 56 individuals in two cohorts yielded 21,293 single nucleotide polymorphisms (SNPs), and 3871 SNPs per individual were retained. The neutral genetic diversity remained stable over time. The 2015 cohort showed positive inbreeding, with one full-sibling pair identified in each cohort. Body size comparisons indicated a significant reduction in disc length and width in the 2022 cohort. Conclusions The smaller body size of the 2022 cohort may hint at increased fishing pressure, but genetic diversity has not been affected. Thus, the null hypothesis is accepted. Implications These findings provide insights into the genetic diversity of Fiji’s maskray and enable a genetic comparison with current Neotrygon species known in the region. Taxonomy confirmation is needed, but the presence of a cryptic or potentially new maskray in Fiji seems plausible.
Context For sharks, information on the location and usage of critical habitats is rare. Marine protected areas (MPAs) have great potential to benefit shark populations but these rarely protect a species throughout its life stages or all critical habitats. The latter often includes parturition sites. Aims Pregnant bull sharks from the Shark Reef Marine Reserve in Fiji were tracked into riverine systems during three parturition seasons. Methods We tagged 31 female bull sharks with acoustic transmitters and placed acoustic receivers in the Rewa, Sigatoka, Navua and Ba Rivers on the island of Viti Levu between 2016 and 2018. Key results Fourteen bull sharks were detected by receivers placed in the four rivers for few, typically consecutive days during parturition season. Bull sharks were detected in the Rewa River during all three parturition seasons whereas sharks were detected in the Navua River only during the 2017/2018 season. Conclusions We have shown that Fiji’s rivers are critical for the completion of the bull shark’s life cycle. Implications Fiji has recognized the importance of conserving its population of bull sharks. Our results call for the implementation of protective measures for the species’ critical habitats.
Data on the reproductive biology of elasmobranchs are essential for understanding their life history. Published studies on batoid ray reproductive biology are comparatively scarce, leading to limited understanding and data gaps. The Oceania fantail ray, Taeniura lessoni, is a good example. This Data Deficient nearshore stingray is restricted to Melanesia, with lacking biological and ecological data, including reproduction. To expand upon the limited life-history data for this species, this short paper provides observational data on the reproductive condition in female T. lessoni, at Drawaqa Island, Fiji. Field work involved direct observations and ocean temperature measurements. Over 40 days spanning three months, 105 surveys were conducted across five sites, resulting in 71 sightings of the species. Based on spot patterns and body markings, four female individuals were identified. Between January and March 2024, these females exhibited convex dorsa indicating advanced gestation, transitioning to concave dorsa suggesting parturition. The presence of neonates from early March onwards coincided with the estimated parturition period inferred from the rays' condition. Furthermore, a female previously pregnant was photographed with a dermal abrasion around her pectoral fin, possibly indicating pre-copulatory biting, suggesting a continuous reproductive cycle. The average monthly water temperature at the surveyed sites remained relatively stable throughout the study. Collectively, our findings suggest that Drawaqa Island provides suitable habitat niches for reproductive activities in female T. lessoni. Repeated and long-term data is certainly needed to confirm either a continuous reproductive cycle or seasonal peaks. While preliminary, our observational data represents the first documentation on female reproductive condition in a stingray in Fiji.
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