Scientists map diving patterns of sharks and rays for first time

By Danny Halpin via SWNS

The diving patterns of sharks and rays have been mapped for the first time in an effort to improve conservation initiatives.

It is the first global study of how elasmobranchs - sharks, skates, rays - move vertically, ranging from the most mysterious deep-divers to those that live at the surface.

By analyzing data from 989 biotelemetry tags, which communicate behavioral information remotely, the team of 171 researchers followed 38 species of elasmobranchs from the North Pacific to the Indian Ocean and the Arctic to the Caribbean.

Researchers say it provides important new insights into the behavior of these ocean giants that will help improve conservation management by filling in data gaps.

More than a third of all sharks and rays are threatened with extinction, according to the IUCN (International Union for Conservation of Nature) Red List of Threatened Species.

Having a three-dimensional map of how elasmobranchs use the aquatic space can help conservationists better understand the roles they play in their ecosystems and how they are exposed to threats.

Study co-lead author Dr. David Curnick, of the Zoological Society of London (ZSL), said: “The way that large marine animals use the horizontal space in our ocean has been well studied.

“However, until now, comparative studies in the vertical planes have been limited, despite the ocean being an average 3.5 kilometers deep and elasmobranchs occupying all levels within this dynamic environment.”

“Investigating how elasmobranchs use the vertical dimensions of their habitat is key in understanding the way they live, but also how anthropogenic stressors are impacting them.

“This helps us to find ways to better protect them through more informed monitoring strategies for example.

“By looking at a wide range of elasmobranch species in this study, we demonstrate how they face overlapping risks, such as targeted fisheries and getting caught in nets, also known as bycatch.”

The work, led by ZSL and Stanford University and published in the journal Science, found that 13 species dive deeper than one kilometer.

Whale sharks dive to a staggering 1,896 meters while white sharks were recorded diving deeper than 1,200 meters.

Some species vary their depth in different parts of the world and this also changes between night and day as the predators move up and down in the water.

Although it was not confirmed exactly why species that normally live at the surface dive into deeper waters, the study suggests it is likely a combination of looking for food, regulating body temperature, reproduction and avoiding other predators.

While many species take deep dives, 26 of the 38 species, including the oceanic whitetip shark, tiger shark, scalloped hammerhead and silky shark, spent more than 95 percent of their time in the top 250 meters, where they are most likely to come into contact with fishing gears.

Co-lead author Dr. Samantha Andrzejaczek, of Stanford University, said: “This massive dataset provides new insights into the vertical movement patterns of sharks and rays on a global scale for the first time.

“This is an important step for both understanding which sharks and rays are most likely to face threats, but also to consider how changing temperature and oxygen levels may influence their vertical distributions.”

It is expected that climate change will alter the chemical composition of the oceans and the availability of oxygen.

As a result, many species will be driven into unfamiliar territories and habitats so having a better understanding of these ecologies could lead to better predictions on how these changes will affect sharks, skates and rays at various depths.

Ernesto Bertarelli, of the Bertarelli Foundation, said: “I’ve seen for myself the terrible threats that shark populations face around the world and how they have been decimated in recent decades.

“I hope that this incredible research will help scientists, conservationists and fisheries managers better protect these astonishing – and hugely important – species in the future so that they can retain their rightful place in the ocean.”

Dr. Curnick added: “Knowing just how deep some species dive (or don’t dive), will help us to inform much-needed conservation plans for these species and their relatives – for example, more widespread use of bycatch avoidance strategies.

“It will also help us understand how these animals are likely to respond to the predicted climate-induced changes to our oceans.”