DIVING NEWS

Mystery rays under investigation

Picture: MMF.

Two species of the shark-like rays known as wedgefish have been tagged by Marine Megafauna Foundation (MMF) scientists for a first-of-its-kind study in Mozambique. 

The white-spotted guitarfish or bottlenose wedgefish (Rhynchobatus australiae) and the bowmouth guitarfish or shark ray (Rhina ancylostoma) are both IUCN-listed as Critically Endangered. They are particularly vulnerable because of their slow growth, late maturity and low reproduction rates.

The wedgefish are, like other rays, caught for their fins. However, so little is known about their biology or ecology that few management plans exist, says the MMF.

The Mozambique study is taking place in the protected Indian Ocean waters of the Bazaruto Archipelago National Park and Vilanculos Coastal Wildlife Sanctuary, with MMF working alongside park staff to identify primary aggregation sites.

The tags are a combination of acoustic transmitters, which send signals that can be picked up by listening stations for up to five years, and six-month pop-up archival satellite tags that record depth, temperature and light-level data. The two types provide the researchers with distinct but complementary information.

“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 MMF co-founder and project co-lead Dr Andrea Marshall. “This will help to identify areas of critical habitat that must be prioritised for protection.

27 July 2021

“We are very excited to see what the tags can tell us about these curious animals. With such little information available, we truly aren’t sure what to expect.” Additional tags will be deployed in the coming months.

The work is supported by the Blue Action Fund, the Mohamed bin Zayed Species Conservation Fund, Ocean Wildlife Project and private donors. More on MMF here. 

*******  CLOSER TO HOME, ROV footage captured in Loch Melfort on Scotland’s west coast has identified an important nursery ground for another Critically Endangered species, the rare flapper skate. 

It’s only the second such area confirmed around the Scottish mainland, scuba divers having helped to identify a similar site in the marine protected area (MPA) covering the Inner Sound of Skye.

Loch Melfort lies in the Loch Sunart to Sound of Jura MPA. Environmental charity Open Seas used what it calls its ClamCam to video 20 egg-cases between boulders, and says both finds demonstrate the effectiveness of seabed protection.

The egg-cases, also known as mermaid’s purses, take some 18 months to hatch, so are vulnerable to disturbance by bottom-trawling and dredging in unprotected areas.

Flapper skates, which can grow to 3m in length, were once common in the north-east Atlantic. Loch Melfort banned trawling and dredging in 2009 and became an MPA for flapper skate seven years ago.