Back to basics: bottlenose wedgefish biology
Protecting threatened species means knowing enough about their biology to make informed decisions about how to manage their populations. To help fill the gaps in knowledge about a highly threatened shark-like ray, Brooke will be investigating the biology of two populations of the Critically Endangered bottlenose wedgefish: one from South-East Asia (Singapore, Indonesia and Malaysia) and the other from northern Australia.
Brooke D’Alberto
For as long as I can remember, I have felt connected to the ocean. I grew up in a small, coastal town in Victoria, Australia, surrounded by the sea. To the south, my entry point into the marine world comprised a sharp, rugged, yet beautiful coastline. Known to the locals as ‘the back beaches’, it is exposed to the strong currents of the Bass Strait. I would spend my weekends exploring the rocky tide pools, in awe of creatures that could survive in such a harsh environment. By contrast, the northern shoreline was washed by the calm, clear waters sheltered...
Life history of the critically endangered ray, bottlenose wedgefish Rhynchobatus australiae
This project aims to document the biology of a critically endangered wedgefish to inform their conservation and management. The specific objective is to determine the species’ age, growth, and maturity from two populations of R. australiae, and then develop methods for estimating growth when little data is available from adults.
While the majority of the methods in the project are well established, there is a lack of information on wedgefishes, and this is a very timely and much needs study on the biology of a critically endangered wedgefish. There is only one age and growth study on Rhynchobatus species by White et al 2014. The life history information was reported as species complex, as it was thought to be three different species of wedgefish along Eastern Australia. This paper was not able to investigate the reproduction of the wedgefish. One study in one region is not sufficient to understand the life history of species, especially if there is considerable regional variation.
Furthermore, we will develop a new method to predict the adult age and growth from the juvenile data, which will assist studies when there is information on the juveniles and lacking information on the adults.
Management and conservation efforts for threatened species can be hampered by the lack of life history and demographic information. Wedgefishes have been listed on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II, which will help ensure that the trade of these species is sustainable and will not continue to endanger the populations. Life history information will be required to assess fisheries risks and inform Non-Determinant Findings (NDFs) for CITES parties. However, with only one study on the age and growth of wedgefish (from the eastern coast of Australia), there is limited information available to do this.
The most commonly caught wedgefish in fisheries is the bottlenose wedgefish, Rhynchobatus australiae. This species reaches a maximum size of 300 cm total length TL and is found throughout the Indo-Pacific. They are commonly found in the Singapore fish markets, where they have been imported from other South-East Asia countries, such as Indonesia. While in Australia, R. australiae are commonly caught as bycatch in the Northern Prawn Fishery (NPF). However, the individuals being caught are mostly small juveniles in the NPF and only small wedgefish are seen in the Singapore fish markets.
Accurate estimates of age and growth parameters rely on an even spread of data across size classes. When size classes are missing from the dataset, back calculation techniques can be used to add interpolated data based on large size classes, to fill gaps in the growth curves caused by missing length classes. However, there is currently no method that can retrospectively account for the missing large individuals.
- Determine the age, growth and reproduction of R. australiae from two populations, one in South East Asia (mainly Indonesia), and northern Australia. The two populations will be compared to investigate any regional differences in life history.
- Investigate and develop methods estimating growth when the samples has juveniles but little or no data is available from adults.
- Publish the research of the two objectives as a scientific paper in a respected and relevant international peer-reviewed journal and provide plain English summaries/policy briefs for fisheries and environmental managers (e.g. CITES).