First assessment of life history and spatial ecology of the endemic Raja Ampat epaulette shark (Hemiscyllium freycineti) in the Dampier Strait, Indonesia

Résumé fourni par la source

The Raja Ampat epaulette shark ( Hemiscyllium freycineti ) is an endemic species inhabiting shallow coastal habitats of the Raja Ampat Archipelago, Indonesia. Despite recent legal protection, information on its biology, population structure, and spatial ecology remains limited, constraining effective conservation. To address these gaps, a total of 64 nocturnal surveys (averaging 1.8–2.3 hours each) were conducted between February 2024 and April 2025 at six sites in the Dampier Strait region. Using photo-identification and passive integrated transponder tagging, 736 unique individuals were identified from 1,191 sightings, with most records from Arborek Island (n = 602). Of these, the population comprised 415 females and 321 males, resulting in a significantly female-biased sex ratio. Total length (TL) ranged from 19.4 to 75.0 cm (mean = 51.1 cm), and body mass ranged from 24 to 1,025 g (mean = 412.8 g). The length–weight relationships indicated negative allometric growth in both females ( b = 2.91) and males ( b = 2.81). Estimated length-at-maturity was 56.59 cm TL for females and 56.42 cm TL for males, with no significant difference between sexes. Relative density ranged from 333 to 2,462 individuals per km², representing the highest population density recorded globally for Hemiscyllium . A total of 256 individuals were resighted at least once, with resighting intervals extending up to 451 days. Immature individuals exhibited significantly higher growth rates than mature ones (7.8 vs 2.8 cm year -1 ), while no sex-specific difference in growth was detected. The best-supported and biologically meaningful growth model, seasonally oscillating ELEFAN with simulated annealing, estimated an asymptotic length ( L ∞ ) of 79.6 cm for all individuals, with a growth coefficient ( K ) of 0.747 year -1 . Growth showed pronounced seasonal oscillations ( C = 0.915). Sharks were most frequently observed in seagrass meadows. Habitat use analyses revealed ontogenetic partitioning. Coral reefs appear to function as a nursery habitat with 69% immature sharks, while seagrass and sand habitats supported higher proportions of adults. Individuals were highly resident, showed no inter-site movement, and occupied small spatial ranges, with maximum net displacements of 475 m. Collectively, these findings provide the first demographic and spatial baseline for H. freycineti in Raja Ampat.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.