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 have prematurely detached from two sharks
- Investigators suspect that in one case, a fisherman accidentally caught the shark and removed its tag.
- Conservation biologist Adam Stow says monitoring research is vital to the species’ recovery.
“It could be in someone’s house, it could be buried in the sand, that’s a real mystery, but does anyone know more about that label,” said marine biologist Dr. Carley Kilpatrick.
It is one of two tracking tags prematurely removed from gray nurse sharks just months after they were affixed as part of a program to track the species’ movements along the East Coast, where the population has been reduced to less than 2,000.
Dr Kilpatrick, a senior conservation officer with Queensland’s Department of Environment and Science (DES), said the miniPAT tracking tags were initially attached to nine sharks at Flat Rock in Moreton Bay in September last year.
The tags are helping SeaWorld and DES researchers document important sites used by sharks and identify any new locations the species is using as the climate changes, so they can protect themselves.
two lost tags
Tracking tags are usually attached to or near the dorsal fin and are programmed to come out and float to the surface on a certain date so that they can then transmit GPS signals and be retrieved by researchers.
“We get a summary of the data from a satellite transmission, but if we retrieve the tag, we get the full data set,” Dr. Kilpatrick said.
The missing tag that was sending confusing location transmissions belonged to a 1.9-meter male gray nurse shark.
“It has appeared about 600 kilometers from the east coast [near the] Coffs Harbor area [on December 20] and then within a few hours it sent a signal to Boambee Bay as well,” he said.
The tag sent out its final transmission on December 22, but had sent out strange signals from the ground before going silent.
“Maybe someone has been on a charter fishing boat [trip]took a flight back to Coffs [Harbour] and then he didn’t know what to do with the label and he threw it overboard,” said Dr. Kilpatrick.
Another tag prematurely emerged from a 2.8m mature female on December 26 and was last detected northeast of Yeppoon on the Capricorn coast on January 8.
“We don’t know exactly what happened, but it was floating on the surface of the water and then it went quiet,” Dr. Kilpatrick said.
common misunderstanding
Dr Kilpatrick said the team needed to learn more about the species in order to protect pregnant females during migration.
“We’re actually trying to find another lost gestation site for these sharks and make sure they’re protected in these areas,” he said.
Adam Stow, a conservation biologist who has been studying the species for about 20 years, said the sharks migrate twice a year from southern New South Wales to central Queensland.
About 1,500 to 2,000 gray nurse sharks live off the east coast of Australia, but the breeding population is about 400 sharks.
“A combination of their natural history traits and the fact that they were overfished has made them critically endangered,” he said.
“One of the reasons the gray nurse shark declined was because, for a time, they were considered a dangerous species to people.
“They’re not man-eaters, but that was certainly a misconception from a few decades ago.”
He said gray nurse sharks grew to about three meters in length, took 10 years for females to mature, and had a maximum of two pups every two years.
“If you knock the population down, it takes a long time to recover because they have a very slow reproduction rate,” he said.
How can you help
Associate Professor Stow said the monitoring program and other citizen science projects were vital to the shark’s survival.
“It is vitally important, we need to know where they are [aggregation sites] and if they are changing,” he said.
As the shark was known to aggregate at particular sites, people were often given the “false impression” that the population was robust.
“That’s why they are a popular species for ecotourism, you can dive at that site and see dozens of individuals,” he said.
“[But] the science is solid: there are low numbers overall.”
Dr Kilpatrick urges anyone with the tags, or any information on them, to contact DES on 07 3101 2085.
“Watch out for the tag if you see it floating in the water, or if it gets caught in a net, or if someone has this tag on their boat or has found it, please return it to us,” he said.
“When people are fishing, if you accidentally catch a gray nurse shark, whether you’re a recreational fisherman, a charter fisherman or a commercial fisherman, you need to know how to identify them.
“We need to release them as soon as possible and if unfortunately the shark has died, keep the tag. If the shark is alive, leave it.”