Deep connections

HIMI sits on the Kerguelen Plateau, isolated from Antarctica and other parts of the world by the deep sea and the Antarctic Circumpolar Current.

It is home to a diverse range of deep-sea benthic invertebrates including seastars, urchins and octopus.

Despite this isolation, Dr Sally Lau, from James Cook University, said preliminary genetic data suggests evidence of both biological isolation within HIMI, and connectivity between HIMI and other parts of Antarctica.

“We’ve seen brittle stars at HIMI that are closely related to those in South Georgia on the opposite side of Antarctica. And there are HIMI sea stars that are closely related to those from near the tip of South America,” Dr Lau said.

Through SAEF, Dr Lau is now using high resolution DNA sequencing to measure connectivity at different depths around HIMI and across hundreds of kilometres.

To assist her project, Dr Cleeland and Dr Appert collected some of the 1000 benthic invertebrates known to live around HIMI and snap froze them for transport back to Australia.

“Antarctic marine invertebrates are known for their adaptation to the cold and dark Antarctic waters, and these high-quality specimens will enable us to unlock their secrets on how they have been surviving in this harsh environment,” Dr Lau said.

The research will ensure variants within species are represented in any future management measures, as well as help to identify new species.

Skate survival

Kerguelen sandpaper skates are a common bycatch species in the HIMI fishery. While all healthy skates caught are released alive, scientists don’t know how many survive the capture and release process.

“Skates grow slowly and mature late, which means their populations can be vulnerable to fishing,” Dr Appert said.

Currently, models designed to predict future population trends consider that all skates released back into the ocean survive.

To determine if this is true, 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 depth and activity patterns once the animals were returned to the ocean.

The tags detached and surfaced after 30 days, to transmit their data to satellites.

“We found most skates went straight to the seafloor and remained there, but some made vertical migrations of up to 400 metres,” she said.

“As skates live on the seafloor, the fact that they stay there doesn’t mean they’re dead. We expected them to be fairly sedentary.”

Dr Appert will now compare the activity patterns of all the tagged skates, to see if she can identify signals that indicate whether the skates are alive.

Combined with the blood chemistry, the results will inform a bycatch population assessment, as well improve understanding of skate physiology and behaviour.

Tagging toothfish

To improve stock assessments and catch advice for Patagonian toothfish, AAD stock assessment scientist Dr Cara Masere is tagging the deep-sea fish to better understand their movement and activity.

“We have a lot of information on the biology of toothfish, and good abundance estimates from historical catches and scientific surveys that are conducted during fisheries activities,” Dr Masere said.

“But we need to know more about what happens below the surface to ensure we’re assessing all that information correctly. How deep and how far they move is integral to getting correct estimates and understanding what the population is doing.”

To assist Dr Masere, Dr Cleeland and Dr Appert attached 21 pop-up satellite tags to toothfish, with 11 released after two months and the rest set to release after one year.

“This is one of the largest tagging studies for Patagonian toothfish in the Southern Ocean, and so far 10 tags have been retrieved and provided movement profiles,” Dr Masere said.

“We’ll be able to look at these movement profiles alongside seafloor bathymetry and ocean current data to see what we can learn. This is the start of piecing the puzzle together and everything we learn is completely new.”

Consulting the bones

To help understand the population structure of Patagonian toothfish populations, researchers like the AAD’s Mr Andy Nicholls, conduct ageing studies on the fish caught, using their ear bones or ‘otoliths’.

“Like tree rings, otoliths contain annual growth rings made of calcium carbonate, which we use to age individual fish,” Mr Nicholls explained.

The AAD has a collection of otoliths from 163,000 fish, and a database of information relating to the sex, weight and length of each fish, as well as where, when and how each fish was caught. The oldest toothfish in the collection is estimated to be 67 years old.

During the voyage, Dr Cleeland, Dr Appert, and scientific observers, collected otoliths and associated data to add to the collection.

Using this information, scientists can better define the age structure of the toothfish population, the preferred habitats of juveniles and adults, and which age groups are particularly susceptible to fishing gear.

Models developed using this information allow the Australian Fisheries Management Authority and the Commission for the Conservation of Antarctic Marine Living Resources to set precautionary catch quotas for the toothfish fishery at HIMI.

“This voyage was a great example of collaborative science and how industry and scientists can work together to conduct research that benefits both interests and helps minimise or avoid impacts on the broader ecosystem,” Dr Cleeland said.

2022-012 Quantifying post-release survival of skate bycatch in the Heard Island and McDonald Islands (HIMI) Patagonian Toothfish longline fishery is supported by funding from the FRDC on behalf of the Australian Government