Discovery of unexpected deep diving in albatross could help protect them from fishing gear
19 January 2022
New research from the University of Oxford’s OxNav team, and published in the journal Current Biology, shows that black-browed albatross are able to dive much deeper than previously thought.
These findings will help both conservationists and fishers to design new and better strategies to prevent albatrosses from being accidentally caught by baited hooks in deep water.
The iconic albatrosses are some of the world’s most threatened species. A large factor driving their decline is mortality when birds are incidentally caught by so-called longline fishing techniques deployed to catch large ocean-going fish. Albatrosses and other species caught this way are known as bycatch.
Albatross are supreme fliers, wandering the oceans almost effortlessly by extracting energy from the wind gradients using dynamic soaring. Consequently, they have never been seen as proficient divers unlike many of their relatives.
Using state-of-the-art miniature biologging devices, the researchers found that black-browed albatross from the Falkland Islands are in fact capable of diving much deeper that previously thought for any albatross species. They do this mainly by propelling themselves using a combination of wings and feet.
In 2019, the team deployed biologgers on a population of black-browed albatrosses breeding on New Island in the Falklands. The biologgers record the GPS location, depth, and speed of tagged albatrosses, helping them to understand exactly how they behave at sea. They found that the albatrosses from New Island were often commuting to the South American coast, where they performed surprisingly deep diving. 50% of birds dived deeper than 10m and that dives could be up to 19m deep. Diving was restricted to daylight hours, and so albatross are probably relying on vision to pursue prey on these dives.
“The use of accelerometers allowed us to see that albatrosses probably began dives sitting on the surface, flapping their wings to propel themselves underwater” - Dr Ollie Padget
They don't yet know what the albatross are after during these deep dives, but this capability suggests that measures to mitigate by-catch in pelagic longline fisheries, a major cause of global decline in many albatross species, might need to be re-examined if albatross can chase baited hooks to much greater depths than previously thought.
In general, historic observations (and some studies with more modern dataloggers) have suggested that albatrosses are surface feeders and so bycatch occurs primarily while lines are being set, when hooks are close to the surface. Since albatross are thought to be unable to dive to depths where the hooks are actively deployed, ways to reduce the availability of hooks to birds while hooks are close to the surface have been deployed.
“We found that deep diving was restricted to daylight hours, and so one potential mitigation could be for pelagic long lines to be set at night when albatrosses might be less likely, or able, to chase baits and become caught” - Dr Ollie Padget
Black-browed albatrosses (courtesy of Tim Guilford)