Featured News Barriers in a sea of sharks and rays

Media Releases

Thu, 16 Sep 2021

Barriers in a sea of sharks and rays

Grey reef sharks
Grey reef sharks in the Coral Sea. Image: Maximilian Hirschfeld

A new study of sharks, rays and skates shows there are many marine barriers in the ocean that can limit the movements of these animals and the exchange of genetic information.

This natural process is a major driver of marine biodiversity, including more than 1000 elasmobranch (shark, ray and skate) species.

But when marine barriers limit genetic connectivity among populations of the same species, they may also reduce their resilience and ability to recover from losses.

James Cook University PhD candidate Maximilian Hirschfeld, who led the study, said when most people think of elasmobranchs, they picture large creatures that roam vast and interconnected oceans.

“In fact, the ocean is a patchwork of diverse aquatic environments that are subdivided by landmasses, changes in ocean depth, temperature, and salinity.

“These subdivisions can pose barriers to the movements of marine animals that are adapted to very specific environments, which reduces the exchange of genetic information among populations,” said Mr Hirschfeld.

He said the scientists’ goal was to show how marine barriers and elasmobranch ecology shape genetic connectivity in the ocean.

The team analysed 173 publications examining the genetic structure of 70 species of sharks and 32 species of skates and rays.

“We found 45 unique marine barriers. For example, deep ocean trenches, drastic changes in temperature and salinity, ocean currents, and even large river deltas, can limit genetic connectivity in sharks and rays at large to surprisingly small spatial scales,” said Mr Hirschfeld.

He said some large oceanic species, such as plankton-feeding basking sharks, can maintain global connectivity. But smaller species that live close to the seafloor and in shallow water can lack genetic exchange across deeper water at distances of less than 100 km.

“The impact of barriers on connectivity also depends on the ecology of individual species. We found that ecological factors, including the habitat a species lives in, how deep it can dive, and its body size, are good indicators for its capacity to move across potential barriers,” said Mr Hirschfeld.

He said studying the connectivity of elasmobranch populations, and of marine species in general, is central to fisheries and conservation management.

“It provides an estimate of long-term resilience and capacity to recover from exploitation and adapt to climate change. With a third of shark and ray species under threat globally we depend on this kind of information to make smart and efficient choices that keep marine populations healthy in the future.”

Image available here. Image use must credit Maximilian Hirschfeld. The image is copyrighted property of Mr Hirschfeld and is not available for use outside of the context of this press release, or for archival purposes or for resale.

Maximilian Hirschfeld:
James Cook University (PhD student)
Associated Researcher, Galapagos Science Center

Affiliations of all authors:
Maximilian Hirschfeld1,2 | Christine Dudgeon3 | Marcus Sheaves1,4 | Adam Barnett1,4

1College of Science and Engineering, James Cook University, Townsville, Queensland, Australia
2Galápagos Science Center, Universidad San Francisco de Quito, Isla San Cristóbal, Galápagos, Ecuador
3School of Biomedical Sciences, The University of Queensland, Saint Lucia, Queensland, Australia
4Marine Data Technology Hub, James Cook University, Townsville, Queensland, Australia

This study was supported by the Galapagos Conservation Trust, The Rufford Foundation, Sea World Research and Rescue Foundation,
the Ecological Society of Australia and the Holsworth Wildlife Research Endowment.


Maximilian Hirschfeld
E: maxh@enphocus.net