Preliminary life history of the Critically Endangered bottlenose wedgefish Rhynchobatus australiae from Southeast Asia

The bottlenose wedgefish Rhynchobatus australiae has experienced substantial population declines throughout its range. However, there is a lack of life history information (age, growth, and maturity) available for this species to inform conservation and management efforts. A total of 48 R. australiae samples were purchased from 2 fishing ports in Singapore between July 2018-July 2019. Species identification was confirmed by mtDNA barcoding using the NADH2 region. Length of specimens ranged from 506-1645 mm total length (TL), and ages ranged from 0-11 yr. Multi-model analysis was used to estimate growth parameters using a Bayesian approach with informative priors. The von Bertalanffy model was the best fitting growth model for the combined sexes (L∞ = 2814 mm TL; L0 = 517 mm TL; k = 0.07 yr-1), for females only (L∞ = 3053 mm TL; L0 = 504 mm TL; k = 0.06 yr-1), and for males only (L∞ = 2741 mm TL; L0 = 497 mm TL; k = 0.07 yr-1). Preliminary results indicate that females and males may mature at different ages and lengths, with females (A50 = 3.25 yr; L50 = 1014 mm TL) matured younger and at smaller sizes, than males (A50 = 5.03 yr; L50 = 1197 mm TL). R. australiae has an estimated theoretical longevity of 40 and 47 yr for males and females, respectively. This study provides the first preliminary species-specific life history information for R. australiae, suggesting that this species in Southeast Asian waters is slow-growing. This information will further the biological knowledge available for this species and can be used to help design effective management and conservation measures.