Understanding the migration pathways of sharks and rays is the key to conserving some of the world’s most endangered marine species, according to new University of Queensland research.
School of the Environment researchers analysed 30 years of satellite tracking, acoustic and mark-recapture studies to map how migratory shark species connect Australian waters with neighbouring countries.
“We shortlisted 29 species that occur within Australian waters, developed network models and built the first cross-boundary migratory connectivity baseline for Australian sharks and rays,” PhD candidate Diego Bezerra said.
“This allowed us to identify which species require international cooperation to support their recovery, and it exposed huge gaps in the available data.”
The research identified whale sharks, blue sharks, shortfin mako sharks, school sharks, and white sharks crossing international borders.
Some travelled as far as South Africa, New Zealand, Indonesia, Micronesia as well as into offshore areas beyond national jurisdiction.
Shark species detected in Australia with transboundary movements between the Australian Economic Exclusive Zone (EEZ) and other jurisdictions, including areas beyond national jurisdiction (ABNJ). For example, Whale Sharks travel to Indonesia, Micronesia, Papua New Guinea and ABNJ.
(Photo credit: Diego F. Bezerra)
Mr Bezerra said these long journeys can expose sharks and rays to threats across multiple jurisdictions and political boundaries.
“Sharks are threatened by overfishing and being accidentally captured when another species is being targeted – blue sharks and school sharks are particularly susceptible to being bycatch,” he said.
Associate Professor Daniel Dunn said the study also highlighted significant gaps in scientific knowledge.
Of the 29 shark and ray species in Australian waters that are listed under the Convention on the Conservation of Migratory Species (CMS), 18 species, or 62 per cent, had no published movement information.
“You cannot manage migratory species by only looking at one part of their migration,” Dr Dunn said.
“Two-thirds of the species we looked at had no information, and you cannot manage species or create policy when you have zero information.
“One of the big problems we have is that these animals don’t breathe air and don’t regularly come to the surface, making them much harder to tag and be detected.
“Other taxonomic groups, such as birds, are much easier to see and track and therefore have much more movement data available.
“We found 8 species with sufficient data to build network models and identified 5 species crossing international borders, so there is a much larger effort required to understand the migration patterns of these animals.”
(Photo credit: Diego F. Bezerra)
Mr Bezerra said the findings highlighted the importance of understanding how shark and ray movements, and the threats they face, extend beyond national borders.
“Australia does a relatively good job of protection but other nations do not always have the same capacity to implement strong measures,” Mr Bezerra said.
“For example, whale sharks are protected here but they migrate to Indonesia where fishing could put them in danger, it is important to understand the different levels of protection between countries.
“It is also important that Australia supports neighbouring nations through collaboration and by sharing technology and information.”
Read the research published in Conservation Biology.
