Feeding patterns among coastal, deep ocean sharks differ, study shows

New analysis of carbon isotopes in shark tissue samples have revealed different feeding patterns among coastal and deep ocean sharks.

Shark populations are declining across the globe, suggesting new and more robust conservation approaches are desperately needed.

The researchers behind the latest study of shark feeding patterns -- published this week in the journal Nature Ecology & Evolution -- are hopeful that their work will inform new and improved conservation plans.

The research was carried out by 73 scientists from 21 countries. Their findings showed coastal sharks living and feeding near continental shelves participate in a diverse array of food webs. Conversely, deep ocean sharks rely mostly on specific sources of food among regions of cold water in the northern and southern hemispheres.

"We were able to show that sharks living close to land and those that live in the open ocean have very different ways of feeding," Christopher Bird, a researcher at the University of Southampton in England, said in a news release.

There are at least 500 shark species living in Earth's oceans, but many of them remain elusive and their behavior poorly understood. A better understanding of vulnerable and endangered shark species can help ecologists and conservationists better protect them.

Carbon isotopes helped scientists determine the varied nature of shark feeding patterns.

"If an animal feeds in the same place where it was caught, the carbon isotope signals in the shark and phytoplankton will match," Bird said. "However, if the shark has moved between feeding and where it was caught, then the signals will be different."

Coastal sharks were more likely to feature isotopic signatures matching those of the plankton where they were caught.

"Not only that, but we found that within a population, individual sharks specialized on food from different food webs -- either eating entirely different species, or the same species but in slightly different habitats with different plants at the base of the food chain," Bird and his colleague Clive Trueman wrote in The Conversation. "Sharks possibly do this to reduce competition among themselves."

Sharks found in the open ocean were more likely to feature the same isotopic signature, regardless of where they were caught or which species they belonged to.

Researchers suggest updated conservation plans need to reflect the varied nature of the feeding patterns found among coastal sharks, while plans to protect deep ocean sharks must include protections for the unique regions of cold, nutrient-rich water they rely on.

"The areas of the ocean that we found were important feeding grounds for oceanic sharks are also good feeding grounds for other predatory fish such as tuna which, in turn, attract lots of human fishing," researchers wrote. "There are currently no protections for sharks in these regions, and establishing large marine protected areas in parts of the sea that are not used for feeding may do little to conserve oceanic shark populations."

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