Western rock lobsters’ long trek helps WA fisheries sustainable management
Western rock lobsters may be small but the uniquely Western Australian species has the ability to traverse hundreds of kilometres, according to a research by the Department of Primary Industries and Regional Development (DPIRD).
The surprising movement results were discovered as part of a major tagging project, undertaken with the Western Rock Lobster Council and the Institute of Marine Science in Virginia, with funding support from the Fisheries Research and Development Corporation.
The research revealed that many of the non-breeding ‘white phase’ (teenage) lobsters travelled all the way from the shallow waters off Perth and Lancelin to as far north as Steep Point, just south of Shark Bay.
Two recaptured non-breeding ‘white phase’ (teenage) females travelled the furthest.
Dubbed ‘Lindsey’ and ‘Lydia’, the pair were both tagged and released in the ocean near Fremantle in December 2014.
Lindsey was caught off the Dongara coast in February 2015, while Lydia was caught a week later west of the Abrolhos Islands, near Geraldton.
Both had walked more than 400 kilometres, at a rate of about five kilometres per day.
The pair’s journey reflects the vast distances western rock lobsters traverse, offshore from the beach to water depths between 40 to 200 metres, in search of suitable breeding grounds.
While some lobsters tagged at Fremantle do not walk much further than Rottnest, others – assisted by the Leeuwin current – can be found as far north as Shark Bay.
The information from the recaptured lobsters, such as movement, growth and mortalities, helps researchers to inform management strategies to ensure the future sustainability of the State’s fisheries.
The results also provide an insight into how the introduction of quotas in 2010 for western rock lobster commercial operators has affected the fishery.
Recent data indicates there is now more biomass or stock in the water, spread out over a greater area. Measurement records also show growth rates have slowed, suggesting the densities of lobsters in some areas has reached high levels.
A total of 210,000 western rock lobsters were tagged as part of the project in 2014 and continue to be tracked.
As of July 2018, nearly 3000 tagged rock lobsters had been recaptured and reported to the department, representing a 1.5% recapture rate.
The western rock lobster is Western Australia’s largest and most valuable fishery, with a commercial value of $386 million per annum in 2017.
The fishery operates between Shark Bay and Cape Leeuwin using baited traps (pots), with 233 vessels actively fishing in 2017.
Recreational fishers who catch a tagged western rock lobster are encouraged to contribute to the research by notifying the department about their discovery by email or downloading the FishTagWA app.
Fishers should note the tag number, lobster size (carapace length), date, location (GPS if possible), the depth at which it was caught, if a female was carrying eggs, had a tar spot and whether it was kept or released.
If a tagged lobster is legal, fishers are welcome to keep it, if it is not legal (undersized or berried), then it should be returned to the water with the tag still attached.
The department will send fishers who supply recapture information a Scratch ‘n’ Win card and information on the lobster and its travels, as a gesture of appreciation.
More information about the western rock lobster and research is available on the department’s website.