Shy shellfish under scrutiny
The first biological evaluation of Brownlip Abalone reveals it is
Australia’s fastest-growing abalone species
Photos: Mollusc Section, Western Australia Department of Primary Industries and Regional Development
By Bianca Nogrady
If the coastal marine environment was a cocktail party, Brownlip Abalone would be the guest dressed in a nondescript outfit trying desperately to blend in with the curtains.
They are the archetypal shy, retiring creature, and there has been little research on the species since the 1980s. But a new report commissioned by the FRDC is shining more light its way, both on the wild and as a cultured species.
Brownlip Abalone – Haliotis rubra conicopora – is found along the south-western coastline of Western Australia, extending as far around as South Australia.
In an industry dominated by the more eye-catching and lucrative Greenlip Abalone, Brownlip Abalone has long been viewed as bycatch. Its lower commercial value has contributed to the lack of interest in it as a species and as a distinct fishery. There is even debate about whether it is a distinct species, with suggestions it may be a sub-species of the Blacklip Abalone (Haliotis rubra rubra) common to eastern Australian coastlines.
The abalone industry in WA began in 1970, with sales to both domestic and international markets. However, records of Brownlip Abalone catches have only been kept since 1984. The first total allowable commercial catch limit for the species was not set until 1999.
However, interest in the species has been rising in recent years, according to the lead author of the new report, Lachlan Strain, a research scientist from the WA Department of Primary Industries and Regional Development.
Brownlip Abalone catches steadily increased to a peak of just less than 40 tonnes a year between 2008 and 2010, averaging about 35 tonnes more recently. This compares to an annual harvest in WA of about 180 tonnes of Greenlip Abalone.
“Brownlip has become a more important component of the fishery, but until now we didn’t even have basic biological information like growth and mortality rates,” Lachlan Strain says.
This information is essential to any fishery, as it enables an evidence-based approach to setting sustainable catch and size limits.
With this in mind, Lachlan Strain and colleagues undertook a four-year assessment, including a tag-recapture study of 1171 wild Brownlip Abalone across 19 sites. It also included the spawning and rearing of Brownlip Abalone juveniles in commercial aquaculture systems, modelling their growth and spawning biomass, and developing a ‘per recruit’ model and a preliminary integrated length-based model for a Brownlip Abalone fishery.
“The big question was really just understanding the basic biology of the animal,” Lachlan Strain says. But this proved more difficult than expected.
Unlike Greenlip Abalone, which prefers to graze in the open across granite or limestone surfaces, Brownlip inhabits cracks, crevices and caves, which makes it much harder to catch.
“Where they’re found in caves, it was much too difficult to access with divers, to the point where you’re pinned up in little caves underwater trying to get these animals out and it just
becomes too physically dangerous,” Lachlan Strain says.
This was particularly challenging when it came to finding juveniles; the research team struggled to collect any animals under 50 millimetres in shell length in the wild. Instead, the researchers had to rely on juveniles from commercial aquaculture to develop a growth profile for the animal.
This revealed that the Brownlip Abalone is the largest and possibly fastest-growing abalone species in Australia. They grow larger than Greenlip Abalone earlier in their lifespan – before two years of age – and achieve maturity at about four to five years of age and at 120mm in size.
The chair of the Abalone Industry Association of Western Australia, Peter Rickerby, points out that size and spawning maturity are not always the same thing.
“Once they reach around 120mm, which is below the actual legal size limit, they do enter maturity but their spawning potential is not as good at that age,” he says. “When they get fully mature, then their spawning potential is much greater.”
This has implications for setting harvest sizes to ensure maximum spawning capability is maintained. More than three-quarters of the Brownlip Abalone caught in the tag-recapture study were over the legal minimum length of 140mm, and more than half were between 150mm and 170mm.
The researchers concluded that the current industry approach of only harvesting relatively large Brownlip Abalone – much larger than the legal minimum size of 140mm – meant the fishery was relatively resilient to pressure from fishing.
The study also noted that the average size of Brownlip being caught commercially has decreased by about 10mm in recent years. Lachlan Strain says one possible cause could be increased diver efficiency, using two divers at a time instead of one, collecting more abalone from each area visited.
Another explanation is environmental.
“In 2010-11, we had a marine heatwave in Western Australia, and we’ve had higher-than-average water temperature for several years after that, which is generally linked to issues with abalone growth and reproduction,” he says.
But overall, the researchers’ modelling of Brownlip Abalone fisheries suggests it is on the right track for long-term sustainability. Industry has welcomed the findings, and Peter Rickerby says the report will be valuable in helping industry and fisheries managers continue working together to shape the future of the Brownlip Abalone fishery.
“It’s going to give us more accurate information in making the best management decisions for the fishery, in terms of setting total allowable catch limits,” he says.
With WA’s abalone fishery awarded Marine Stewardship Council (MSC) certification in October this year, the research report has come at an ideal time, Peter Rickerby says.
“This report will also be used with the MSC harvest strategies and help us set the total allowable commercial catch and size limits to the right level to ensure we are sustainable,” he says.
Lachlan Strain says the findings are a big step forward for the WA abalone industry. “It’s quite a significant stepping stone for us in terms of managing both the Greenlip and Brownlip abalone fishery in WA.
“Not only does it give us a good handle on Brownlip but we’re also transferring the models developed in this project across to Greenlip and other species, thereby improving the stock assessments for all abalone species in WA.”
The research has also uncovered crucial information to inform the development of Brownlip Abalone aquaculture, which for the moment is relatively small in WA compared with Greenlip Abalone. The study identified a crucial difference between the two species: Greenlip Abalone likes the light, whereas Brownlip Abalone likes the shadows.
“We looked at Brownlip through what would be considered traditional Greenlip aquaculture systems and techniques. We found that in the juvenile stage, when they’re in the nursery, you wouldn’t need to adjust systems – you could still produce them the same way Greenlip is produced,” Lachlan Strain says.
The problem came when they moved to the grow-out system, where Greenlip Abalone are generally housed in concrete slab tanks; Brownlip Abalone were too exposed for their liking and would crawl out of the tank seeking shelter. The animals also huddled together for protection, which reduced their growth rates, he said.
He suggested grow-out tanks for Brownlip Abalone might benefit from being deeper, and with artificial habitats that allow the abalone to lurk out of sight. Their research suggested that even these simple measures could reduce mortality and lead to better growth rates.
“It starts to indicate that regardless of whether they’re in the wild or aquaculture, that behaviour is still there and that you really need to match the animal’s behaviour to your aquaculture systems to get the best out of it,” he says.
FRDC Research Code: 2012-016