While most relocated Southern Rocklobster stay put, those that do move have shown a highly accurate sense of direction
Illustration: Aidan Gifkins A South Australian study involving the translocation of Southern Rocklobster (Jasus edwardsii) has provided new evidence that the species has a magnetic-compass-like capacity to orient itself in unfamiliar waters.
The study was primarily aimed at determining whether pale white rocklobsters found in deep water would change their carapace colour to the brighter red preferred by export markets if they were relocated to shallow water sites.
“However, we were also interested in the movement patterns of individual rocklobsters after the translocation event,” says project leader Adrian Linnane, from the South Australian Research and Development Institute (SARDI).
The results of the research support a long-held theory about rocklobsters’ navigation abilities, and were acepted for publication in the prestigious international scientific journal Marine and Freshwater Research in August 2014.
The translocation study was undertaken in 2007 at Southend, South Australia, about 100 kilometres from the SA–Victorian border. More than 5000 rocklobsters were physically moved from offshore water 100 metres deep, to a shallow, inshore site on Ringwood Reef where the water is less than 20 metres deep.
Adrian Linnane says previous studies of rocklobster movement were based on rocklobsters tagged and released at their point of capture. The recent SARDI study was unique in that it allowed researchers to monitor movement patterns in rocklobsters displaced from their normal environment.
“This study was successful in that the light-coloured deep-water rocklobsters did indeed change to the preferred red colour within 12 months of being translocated.
“In addition, 60 per cent of all recaptures remained within their new inshore environment, with no evidence to suggest that any significant mortalities occurred,” he says.
“While most rocklobsters remained resident, some moved considerable distances in a highly directional nature away from the release site. We found that 40 per cent of the rocklobsters recaptured had travelled in a consistent south-west bearing back out into deeper waters. This supports the theory that rocklobsters have some kind of true navigational sense.”
Adrian Linnane says females travelled significantly further than males, with one female rocklobster recaptured 48 kilometres from the translocation site after 735 days. “That’s quite a distance, considering the only way adult rocklobsters can move is by crawling across the sea floor,” he says.
The reason for the return to specific areas offshore remains uncertain, but researchers speculate that females prefer to release their larvae in offshore currents to improve survival. Information from the research will help inform rocklobster fishery management.
“Given that we now know that rocklobsters move between different regions in the fishery, this supports the view that the resource may need to be managed as a single fishery, rather than discrete spatial units,” Adrian Linnane says.
The SARDI study, ‘Residency and movement dynamics of Southern Rocklobster (Jasus edwardsii) after a translocation event’, was funded by the FRDC. It followed on from a similar translocation project, ‘Spatial management of Southern Rocklobster fisheries to improve yield, value and sustainability’, led by the Institute of Marine and Antarctic Studies at the University of Tasmania, and also funded by the FRDC.
FRDC Research Code: 2014-702
More information
Adrian Linnane, SARDI, 08 8207 5492, adrian.linnane@sa.gov.au
