Signals from missing grey nurse shark tags leave researchers baffled
The movements of a $5,000 satellite tag, originally attached to a gray nurse shark, have baffled researchers tracking and studying the critically endangered species off Australia’s east coast.
Key points: Tracking tags came off two sharks prematurely Researchers suspect in one case a fisherman accidentally caught the shark and removed its tag. Conservation biologist Adam Stow says monitoring research is essential to the species’ recovery
“It could be in somebody’s house, it could be buried in the sand, that one is a real mystery, but somebody knows more about that marker,” said marine biologist Dr Carley Kilpatrick.
It is one of two tracking tags that have come off prematurely from gray nurse sharks just months after they were put on as part of a program monitoring the species’ movements along the east coast, where the population has dwindled to fewer than 2,000.
Gavin Richards is a member of the research team monitoring gray nurse sharks. (Provided: Sea World)
Dr Kilpatrick, a senior conservation officer with the Queensland Department of Environment and Science (DES), said miniPAT tracking tags were initially attached to nine sharks at Flat Rock, in Moreton Bay, in September last year.
The tags help researchers from Sea World and the DES to document important sites used by the sharks and to identify any new locations used by the species as the climate changes.
Two missing labels
The tracking tags are typically attached to or near the dorsal fin and are programmed to pop off at a certain date and float to the surface, so they can then send out GPS signals and be retrieved by researchers.
“We get a summary of data from a satellite transmission, but if we get the tag back, we get the full data set,” Dr Kilpatrick said.
The missing tag that sent confusing location transmissions belongs to a 1.9 meter gray nurse shark.
“It surfaced about 600 or so kilometers from the east coast [near the] Coffs Harbor area [on December 20] and then within a few hours sent a signal at Bombee Bay as well,” she said.
The tag sent its final transmission on December 22, but sent strange signals from land before it went silent.
“Maybe someone was out there on a charter fishing [trip]caught a flight back to Coffs [Harbour] and then didn’t know what to do with the label and threw it overboard,” Dr Kilpatrick said.
Another tag came off a 2.8 meter mature female prematurely on 26 December and was last tracked north-east of Yeppoon on the Capricorn Coast on 8 January.
“We don’t know exactly what happened, but it was floating on the surface of the water and then it went still,” Dr Kilpatrick said.
Dr Kilpatrick said the team needed to learn more about the species to protect pregnant females during migration.
“We’re actually trying to find another missing gestation site for these sharks and make sure they’re protected in these areas,” she said.
Gray nurse sharks are a critically endangered species. (Provided: DES)
Adam Stow, a conservation biologist who has been studying the species for about 20 years, said the sharks migrate from southern New South Wales to central Queensland every two years.
About 1,500 to 2,000 gray nurse sharks live on Australia’s east coast, but the breeding population is about 400 sharks.
“A combination of their natural history characteristics and the fact that they are overfished has led to them being critically endangered,” he said.
“One of the reasons the gray shark declined was because for a while they were considered a dangerous species to humans.
“They’re not cannibals, but that was certainly a misconception from a few decades ago.”
Dr Carley Kilpatrick and members of the research team. (Provided: Sea World)
He said that gray nurse sharks grew to about three meters in length, took females 10 years to mature and had a maximum of two pups twice a year.
“If you knock the population down, it takes a long time to recover because they have a very slow reproductive rate,” he said.
How you can help
Associate Professor Stow said the monitoring program and other citizen science projects were vital to the shark’s survival.
“It is critically important, we need to know where they are [aggregation sites] and whether they are changing,” he said.
Since the shark was known to congregate in specific locations, people often had the “false impression” that the population was strong.
“That’s why they’re a popular species to see for ecotourism, you might dive that site and see dozens of individuals,” he said.
“[But] the science is solid – there are low numbers across the board.”
Researchers are searching for a lost tag in central Queensland and another near Coffs Harbour. (Supplied: Sea World)
Dr Kilpatrick is appealing for anyone who has the tags, or any information about them, to contact DES on 07 3101 2085.
“Keep an eye on the tag if you see it floating in the water, or if it gets caught in a net, or if anyone has this tag on their boat or has found it – please send it back to us,” she said.
“When people are out there fishing, if you accidentally catch a gray shark where you’re a recreational fisherman, charter fisherman, commercial fisherman, you need to know how to identify them.
“We need to release them as soon as possible and if the shark is unfortunately dead, please keep the tag. If the shark is alive, leave the tag.”