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

Abstract

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.