The movements of a $5,000 satellite tag, originally attached to a grey nurse shark, have baffled researchers tracking and studying the critically endangered species off Australia's east coast.
"It could be in someone's house, it could be buried in the sand, that one's a real mystery but someone knows more about that tag," marine biologist Dr Carley Kilpatrick said.
It's one of two tracking tags that have prematurely come off grey nurse sharks just months after they were fitted as part of a program monitoring the species' movements along the east coast, where the population has dwindled to fewer than 2,000.
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 are helping researchers from Sea World and the DES to document important sites being used by the sharks and to identify any new locations the species is using as the climate changes, so they can be protected.
Two missing tags
The tracking tags are typically fitted on or near the dorsal fin and are programmed to pop off and float to the surface on a certain date, so they can then transmit 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 belonged to a 1.9-metre male grey nurse shark.
"It's popped up about 600 or so kilometres off the east coast [near the] Coffs Harbour area [on December 20] and then within a few hours it sent a signal at Boambee Bay as well," she said.
The tag sent its final transmission on December 22, but had sent odd signals from land before going quiet.
"Maybe someone's been out there on a charter fishing [trip], caught a flight back to Coffs [Harbour] and then not known what to do with the tag and thrown it overboard," Dr Kilpatrick said.
Another tag prematurely popped off a 2.8-metre mature female on December 26 and was last detected north-east of Yeppoon on the Capricorn Coast on January 8.
"We don't know exactly what's happened but it's been floating around on the surface of the water and then it went silent," Dr Kilpatrick said.
Common misconception
Dr Kilpatrick said the team needed to learn more about the species to protect gestating females during migration.
"We're actually trying to find another missing gestation site for these sharks and make sure that they're protected in these areas," she said.
Adam Stow, a conservation biologist who has been studying the species for about 20 years, said the sharks migrate biannually from southern New South Wales up to central Queensland.
About 1,500 to 2,000 grey nurse sharks live on Australia's east coast, but the breeding population is roughly 400 sharks.
"A combination of their natural history traits and the fact that they were overfished, has led them to be critically endangered," he said.
"One of the reasons the grey nurse shark declined was because they were viewed, for a little while, as a dangerous species towards people.
"They're not man-eaters, but it was certainly a misconception from a few decades ago."
He said grey nurse sharks grew to about three metres in length, females took 10 years to mature, and had a maximum of two pups biannually.
"If you knock the population down it takes a long time to recover because they have a very slow rate of reproduction," 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's critically important, we need to know where they are [aggregation sites] and whether they're changing," he said.
As the shark was known to aggregate at particular sites, people often had the "false impression" that the population was robust.
"That's why they're a popular species to view for ecotourism, you might dive that site and see dozens of individuals," he said.
"[But] the science is solid — there are low numbers overall."
Dr Kilpatrick is urging anyone who has the tags, or any information about them, to contact DES on 07 3101 2085.
"Keep an eye out for 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 return it to us," she said.
"When people are out there fishing, if you do accidentally capture a grey nurse shark, whether you're a recreational fisher, charter fisher, commercial fisher, you should know how to identify them.
"We need to release them as soon as possible and if, unfortunately, the shark has died please retain the tag. If the shark is alive, leave the tag in."
