Scientists investigate the ups and downs of shark and ray life

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An international team of scientists, including from the University of Western Australia and the Australian Institute of Marine Science (AIMS), have conducted research into how sharks, rays and rays – also known as name of elasmobranchs – use the depths of the ocean.

“The ocean varies more rapidly in the vertical plane than in the horizontal plane and as these animals move vertically through their three-dimensional habitat, they also experience extreme environmental changes. “

Dr. David Tickler, UWA

The team of 171 researchers from 135 institutions in 25 countries gathered two decades of data from 989 sophisticated electronic beacons that remotely tracked the movements and behaviors of 38 species in oceans around the world, with their findings published in Scientists progress.

Scientists have a wealth of data on the movements of marine species that inhabit the near-surface spaces of the coastal ocean, but the movements of three-dimensional animals, especially in the deeper vertical spaces of the ocean , are less well understood.

Image: A satellite tagged Manta Ray. 1 credit

Dr David Tickler, of UWA’s Marine Futures Lab, said understanding how elasmobranchs use vertical spaces was crucial to understanding their current and future ecological roles in the ocean and the risks associated with various threats. More than a third of all sharks and rays were threatened with extinction according to the International Union for Conservation of Nature’s Red List of Threatened Species.

“Think of human interaction with the ocean such as shipping, fishing and exploration for oil and minerals and proposed activities such as deep sea mining – if we don’t understand how animals use the vertical space, we don’t understand the threats to them,” Dr. Tickler said.

“The ocean varies more rapidly in the vertical plane than in the horizontal plane and as these animals move vertically through their three-dimensional habitat, they also experience extreme environmental changes.

MAP Bullshark

Image: A Bull Shark with a CATS camera on its back. Credit: Ryan Daly

“The way they use this vertical habitat tells us a lot about what’s going on in the ocean, but also how the animals adapt to the different niches in this vertical space.”

The study found that the ocean region receiving sunlight – which extends from the surface to around 200 meters deep – was potentially a danger zone for elasmobranchs and was where they were most likely to be exposed to fishing gear as a target species or by-catch.

Of the 38 species in the study, the researchers found that 26 spent more than 95% of their time in the top 250 meters of the water column.

Dr. Samantha Andrzejaczek, co-lead author of the study and postdoctoral researcher at Stanford University’s Hopkins Marine Station, said one of the common vertical movements in elasmobranchs appeared to correspond to the daily vertical migration of the ocean (twice a day).

At daybreak, tiny fish and invertebrates – followed by the animals that feed on them – begin to migrate from the upper, bright ocean layer to the relative safety of darker, deeper water. At night, they come to the surface to feed.

“We believe that sharks and rays in daily migration follow food resources through the water column,” Dr Andrzejaczek said.

MAP

Image: Dr. Samantha Andrzejaczek with some of the Block Lab satellite beacons. Credit: Andrew Brodhead

The researchers hope their findings will enable policy makers and resource managers to examine the threats these animals face and guide future management and conservation plans.

* AIMS Principal Investigator Dr Mark Meekan, Quantitative Ecologist Dr Michele Thums and Research Scientist Dr Luciana Ferreira were also co-authors of the article “Dipping into the Vertical Dimension of Movement Ecology elasmobranchs.

Photo credit (top): Mark Royer

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