Marine Megafauna Foundation Launches Study Into Critically Endangered Mozambique Wedgefish
Scientists from Marine Megafauna Foundation (MMF) have launched an intensive tagging study into two critically endangered species of wedgefish in Mozambique. The study, the first of its kind to target wedgefish, seeks to better understand their movements and habitat use to develop better protection strategies in the region.
The study will focus around the bottlenose wedgefish (Rhynchobatus australiae) and bowmouth guitarfish (Rhina ancylostoma). Although they have a distinctive shark-like body (wedgfish are often referred to as 'guitar sharks') they are, in fact, species of ray from the familiy Rhinidae, collectively known as wedgefish, recently identified as among the world’s most endangered groups of marine animals. Both are currently listed as Critically Endangered by the IUCN Red List of threatened species.
Like many shark and ray species, wedgefish are slow to grow and reach sexual maturity, with low reproductive rates making their populations particularly vulnerable to overexploitation, especially as their fins are highly valued by the shark finning industry.
MMF's new study is being conducted in the protected waters of Mozambique's Bazaruto Archipelago National Park and Vilanculos Coastal Wildlife Sanctuary. MMF researchers are working alongside park authorities and managers to identify primary aggregation sites for the wedgefish, understand their movements and home range, and identify the threats they face in the region.
The scientists are tracking the wedgefish using two different types of tag: acoustic tags, and pop-up satellite archival tags. Acoustic tags are small transmitters that are detected by an array of underwater receivers whenever a tagged animal comes within a few hundred metres. Researchers collect data from the arrays every few months and the batteries of the acoustic tags can last up to five years, providing valuable long-term movement data.
Pop-up satellite tags (PSATs) are attached to the dorsal fin of the wedgefish and record depth, temperature, and light-level data. The light-level data use sunrise and sunset times to predict the whereabouts of the animal through ‘light-based geolocation.’ The tags remain attached for six months before floating to the surface and transmitting the collected data via the ARGOS satellite network.
The two methods provide different, but complementary, information that can be used to track both fine and broad-scale movements.
'By using this particular combination of tags, we can learn where the animals spend most of their time, whether visits to specific sites are year-round or seasonal, how far they move, how deep they dive, and which temperatures they prefer,' said Dr Andrea Marshall, MMF co-founder and co-lead of the project. 'This will help to identify areas of critical habitat that must be prioritized for protection.'
Little is known about global wedgefish populations, so the scientists hope that the study will divulge new information that can be used to aid their protection.
'We are very excited to see what the tags can tell us about these curious animals,' said Dr Marshall. 'With such little information available, we truly aren’t sure what to expect. They are rare, elusive, critically endangered, and fished intensively for their fins... [and] they require urgent protection.'