Population Status of Two Wedgefish Species in Western Indonesian Inner Waters, Inferred from Demographic Models with Limited Data

Wedgefish (family Rhinidae) is a group of elasmobranchs that experience a global threat due to its highly valued fins. Similar condition happens to most species of wedgefish inhabiting Indonesian waters where fishing activities are intense without sufficient management controls and lack of supporting studies on their sustainabilities. In order to get a picture of wedgefish populations in Indonesia, the current study employing demographic analysis was performed to know the population status of two wedgefish species (Rhynchobatus australiae and Rhina ancylostoma) from western Indonesian waters (including the Java Sea, Karimata and southern Makassar Straits). Age-based matrix models were used involving two scenarios of populations with and without fishing. Monte carlo simulation was applied to incorporate uncertainties in life-history parameters. The results show contrasting productivities for R. australiae and R. ancylostoma. R. australiae is sufficiently productive, indicated by high population growth rates in both with and without fishing scenarios. In contrast, the population of R. ancylostoma grows positively only in the unfished scenario, but the growth is negative in the with-fishing scenario. This finding indicates that the current level of exploitation caused the depletion in the population of R. ancylostoma. The current level of fishing can be maintained for R. australiae to give optimum benefits to fishery communities, while for R. ancylostoma, substantial reduction in fishing is required. Protection of young fish (juveniles up to age at first reproduction) is recommended in both fish since population growths are very sensitive to the changes in these stages.