It's the scientific equivalent of finding a message in a bottle.
In a rare sequence of events, a satellite tag, originally attached to a deep-sea skate off a remote island in the Southern Ocean, has washed up on a beach in southern Tasmania, after travelling more than 5,000 kilometres in 10 months.
The tag, deployed on the skate from a fishing vessel off Heard Island by Australian Antarctic Program scientists, washed up on Bruny Island and was found by a member of the public, Mark Jaffrey.
"I was walking along Cloudy Bay beach at low tide and saw this unusual thing that looked like it could be an explosive, so I didn't want to touch it at first," Dr Jaffrey said.
"But then I saw it had a transmitting aerial on it and a URL with the company's name and I knew it was a marine wildlife tag, so I pocketed it and contacted the manufacturers when I got home.
"I was so pleased when the scientists contacted me and told me what it was, and so pleased that I could return it to them. The data it contains could make a big difference to their research and it sounds like it was one of the better tags to find, in terms of the activity of the skate it was attached to."
Tag - you're it!
What Dr Jaffrey found was one of 45 pop-up satellite tags deployed on Kerguelen sandpaper skates and Patagonian toothfish by Institute for Marine and Antarctic Studies (IMAS) PhD student, Colette Appert, and former Australian Antarctic Division (AAD) fisheries scientist Dr Jaimie Cleeland (now at British Antarctic Survey).
The pair spent 97 days on board the Patagonian toothfish longline-trawling vessel, Cape Arkona, last year, as part of an AAD science-industry collaboration supporting the sustainable fishery around Heard Island and McDonald Islands (HIMI).
Dr Appert's research aims to understand the survival rates of sandpaper skates after release from being caught on fishing lines.
These deep-sea denizens are only found around Heard Island, in waters down to 2,000 metres. They are the most abundant bycatch species in the HIMI toothfish fishery, and fishers are required to release all healthy skates.
Observers from the Australian Fisheries Management Authority are also present on all vessels fishing at HIMI, and record all catches and releases of skates.
To find out how many survive, Dr Appert assessed captured skates for injuries, and then took blood samples to look for stress markers that might reveal the likelihood of survival.
She also tagged 24 skates with pop-up satellite tags, to investigate activity patterns once the animals were returned to the ocean.
The tags detach and surface after 30 days, to transmit a portion of their data to satellites.
"We program the tags to transmit depth, activity and temperature, and a summary of this data is transmitted to the satellite," Dr Appert said.
"But there is a lot of raw data on the tag that we can only access if we recover it - and it's a miracle if that happens.
"The discovery of this tag will allow me to dive into the complete and extremely high resolution data for this skate, and I can't wait."
Vital statistics
Dr Appert said the skate in question was a male measuring 113 centimetres in length, which she named Dedy after a crew member.
"We attached Dedy's tag on 11 May 2023 and it detached on 11 June, ascending approximately two kilometres to the surface and only 1.4 kilometres from its deployment site," she said.
"The data it transmitted to satellite showed Dedy made extensive vertical movements within canyons just 50 kilometres east of Heard Island, venturing down to 1,420 metres and back up to 1,000 metres multiple times.
"The detached tag drifted steadily eastward to its final known location 300 kilometres from Heard Island, and then over the course of 10 months it traversed another 5,300 kilometres and washed ashore at Bruny Island.
"The raw data that we've just downloaded from the tag will give us a really precise read for Dedy's activity, but it will also help us understand the summary data transmitted by the other skates' tags."
Early results from all of the 24 tags' satellite transmissions, received by fisheries scientist Dr Cara Masere at AAD headquarters near Hobart, showed a lot more vertical movement than expected.
"We found most skates went straight to the seafloor and remained there, but some made vertical migrations of up to 400 metres," Dr Masere said.
"Surviving skates are much more active than we expected, travelling up and down the canyons and slopes of the Kerguelen Plateau."
Filling the gaps
As well as a careful review of the recovered tag's data, Dr Appert will soon analyse the blood samples she took. It's the first time blood samples have been collected from deep-sea skates and Dr Appert hopes they will provide insights into the stress response and physiology of this little-studied species.
"This study is another step towards understanding the population's spatial footprint and how it overlaps with fishing activities, and the effect this will have on the species over time," she said.
"The survival rates from my study will fill crucial data gaps that cause uncertainties in skate bycatch stock assessments within the toothfish fishery, which inform fishery management.
"It will also contribute to research on the management of other Southern Ocean fisheries that have skate bycatch."
Dr Masere hopes the 21 Patagonian toothfish tags she's responsible for will also prove similarly successful. Ten of the tags detached in May, one year after being deployed, and 11 released after two months.
"We have a lot of information on the biology of toothfish and good abundance estimates from historical catches and scientific surveys," Dr Masere said.
"But to improve stock assessments and catch advice for Patagonian toothfish, through the Commission for the Conservation of Antarctic Marine Living Resources, we need to know more about what happens below the surface, including how deep and how far they move."
As for Dr Jaffrey, he'll be keeping his eyes peeled for more tags.
"There's another 44 tags floating around out there," he said.
"For all the beachcombers out there, if you see one pick it up and return it because it will make someone's day."
This project was supported by funding from the Australian Antarctic Division, the Australian Fisheries Management Authority, the Fisheries Research and Development Corporation on behalf of the Australian Government, and the Australian toothfish fishing industry. The Marine Stewardship Council Ocean Stewardship Fund also provided a student grant for Colette.
