Fact Sheet: Abalone

Escargot of the sea

Roe’s Abalone are a reef-dwelling marine snail in Western Australia which are the target of one of the world’s shortest recreational fishing seasons. Despite this fishing pressure, WA can boast one of the few remaining sustainable wild-stock abalone fisheries.

Marine snails

Abalone are a type of single-shelled (gastropod) herbivorous marine mollusc. Their body is large and fleshy, with a broad, muscular foot that is used to attach itself to reefs or rocks using suction.

The shells of abalone species are flat and ear-shaped, which protects them from wave action and predation. The inside of their shells are smooth and shiny to protect the soft flesh of the abalone from damage.

Roes abalone front and back

Abalone species are distinguished from other marine snails by a row of small holes or ‘pores’ that run along the edge of their shell.

Abalone expel water that has passed through their gills through these holes. As abalone grow, these holes progressively close-up, with usually only the last 4 to 6 holes remaining open when they reach full-size.

There are 11 abalone species found in Western Australia, but only 3 of them occur in large enough numbers to be fished: Roe’s abalone (Haliotis roei), greenlip abalone (H. laevigata) and brownlip abalone (H. conicopora).

Roe’s abalone have a reddish-brown sculptured shell and are small, measuring up to 11 cm across their shell.

Roe’s abalone with ‘pores’

In contrast, Greenlip shells are smooth, off-white and can measure up to 22 cm, while Brownlip shells are ridged, reddish-brown, and up to 24 cm. Greenlip and Brownlip abalone get their names from the coloured edge or ‘lip’ of their muscular foot.

Greenlip abalone

Brownlip abalone

underside of abalone, from left to right, brownlip, greenlip and Roe’s abalone.

Distribution

Abalone are widely distributed across tropical and temperate coastal areas. Roe’s abalone can be found as far north as Shark Bay in Western Australia and south around to Victoria. They mostly inhabit shallow limestone reefs along the west and south coasts, especially around Perth.

The 2 larger, more valuable species – greenlip and brownlip abalone – are found on reefs in deeper water along Western Australia’s south coast. Brownlip abalone are limited to WA whilst greenlip abalone are also found across southern Australia to Victoria and northern Tasmania.

Map: Distribution of commercially important abalone species in Western Australian waters

Key:    Roe’s abalone (to 5 m depth)

Greenlip/brownlip abalone (to 40 m depth)

Life cycle

Roe’s abalone spawn mostly in winter, while greenlip and brownlip spawn in late spring and summer.

The spawning period for all species is influenced by water temperature and food availability. Female greenlip abalone can produce up to 2 million eggs once they reach 4 to 5 years of age. They release their eggs into the water, where they are fertilised by sperm released by the males. Within 2 days, the fertilised eggs develop into tiny larvae. The larvae drift with the water currents for about a week, feeding and growing before developing their shell.

Fluctuating inshore currents and tides can prevent abalone larvae from dispersing far from the spawning site. Over time, this process has led to the formation of isolated abalone populations across the Western Australian coastline. The young abalone settle into holes and crevices within limestone or granite reefs, where they graze on small algae and diatoms. As they grow, they tend to move into more open areas of the reef, where food is more abundant. In some areas, dense ‘stunted’ populations can develop and show different growth characteristics from other populations. These abalone grow slower than those in highly productive areas and reach a smaller maximum size.

Generally, estimates of the ages of abalone are calculated from growth rates obtained through tagging studies. Roe’s abalone are thought to live to at least 10 years, while greenlip and brownlip may live up to 13 years.

1. Juvenile abalone are found under rocks and in holes and crevices on reefs, grazing on small bits of algae.
2. As they outgrow crevices, abalone tend to move to the more open sections of reef where there are greater amounts of food. Abalone will tolerate high population densities – Roe’s abalone can reach up to 400 animals per square metre.
3. Roe’s abalone reach sexual maturity when they are about 2-and-a-half years old and 4 cm in shell length. The larger greenlip and brownlip abalone mature at 3-4 years of age, when they are about 9 to 10 cm in shell length.
4. Abalone are ‘broadcast spawners’, which means that eggs and sperm are released into the water at the same time.
5. The fertilised egg begins to divide.
6. The fertilised eggs develop into tiny larvae that hatch out during the next 24 hours. The larvae then drift and swim in the water column for about a week until they are ready to settle. The larvae do not feed during this time but may take up some nutrients from the seawater.
7. The larvae actively search for a suitable environment for permanent settlement. When a site is found the larvae settle and begin ‘metamorphosis’ – changing into a crawling ‘post-larvae’ that no longer have the ability to swim.
8. Post-larvae feed on tiny organisms, bacteria and microscopic algae, growing for about 2 to 3 months until their shell develops the first small opening for breathing.
9. At this stage the juvenile abalone are called “spat”. When they reach about 5 mm in length they will start feeding on larger species of algae.

Predators

As with most marine invertebrates, mortality rates of abalone are highest in their larval and juvenile stages, but decrease as the abalone grow. Abalone are preyed upon by stingrays, fish (especially wrasses), sea stars, rock lobsters and octopus.

In response to threats from predators, abalone can clamp themselves hard to the reef using its shell as protection – or move surprisingly fast away from slower-moving predators such as sea stars.

Roe’s abalone attached to a reef

Marine Heatwave

Water temperatures off the south-western coast of WA rose to unprecedented levels during February and March 2011. This heat wave is viewed as a major temperature anomaly. Sudden changes in water temperature have been recorded off the WA coast in the past, but there have been no previous records of such strongly elevated temperatures.

The effect of the marine heatwave on abalone stocks appears to have been more severe than on some other invertebrate species. Abalone aren’t able to move to avoid unfavourable conditions.

Between early February and early March 2011, mortalities on Roe’s abalone were estimated at 99.9% north of Kalbarri. A significant spike in sea surface temperature (SST) in late February appears to have been the trigger, occurring after at least 2 months of elevated water temperatures. Mortalities were also associated with discoloured water, poor visibility and algal blooms, none were shown to be attributable to disease.

The heatwave also affected the Perth metropolitan stock but to a lesser extent.

A complete closure of the commercial and recreational fisheries in the area north of Moore River and monitoring and stock recovery programmes in Kalbarri and Perth were implemented.

The Department undertook a translocation project to investigate the rebuilding of the depleted Roe’s abalone populations. Adult abalone from nearby source populations, along with hatchery-reared juveniles, were relocated to reef systems north of Kalbarri. The project is detailed in the report Recovering a Collapsed Abalone Stock Through Translocation. (Strain et al. 2019) It established new founder populations of effective breeding size and demonstrated that both translocating adults and releasing hatchery-reared juveniles is feasible at remote sites. Whilst no major mortalities were recorded in the Perth fishery, evidence suggests a temporary stunting growth effect in mature age classes that has now ceased (Hart et al 2018).

Fishing for abalone

Roe’s abalone are particularly abundant on shallow reef platforms around the Perth metropolitan area. Approximately 45 tonnes of Roe’s abalone are taken annually by commercial and recreational fishers in this area alone. The reef platforms can be exposed during low tide, making the fishery very accessible for large numbers of people wading out to collect abalone recreationally. Commercial divers target Roe’s abalone that live in deeper water.

Recreational abalone fishers on a reef platform in the Perth metropolitan area.

Commercial fishery

In Western Australia, a commercial fishery was established in the mid-1960s to supply Japanese and south-east Asian markets and coincided with the introduction of SCUBA (Self Contained Underwater Breathing Apparatus) diving.

Divers use ‘hookah’ breathing equipment from small boats (a surface air compressor and air hose) to harvest abalone. Divers prise mature abalone from the reef using a chisel-shaped abalone ‘iron’. Some divers choose to use motorised ‘shark cages’, which provide them with additional protection and enable the collection of abalone over a wider area.

The commercial fishery is managed by Total Allowable Catches across 8 areas in the State. The minimum size limits for abalone vary by species and management area throughout WA.

The popularity and price of abalone worldwide has soared, causing this seafood delicacy to be overfished in many countries and the high value of abalone makes them attractive to poachers and illegal fishing, which remains a problem throughout southern Australia.

Western Australian commercial abalone catch areas

Algae eaters

Abalone have a rasping tongue called a radula. As juveniles they graze on algae encrusted rocks, but as adults they catch food by raising their shell and clamping down on algae as it floats by. As a result, they are therefore found in greatest numbers on those parts of a reef where bits of broken-off algae tend to collect.

Roe’s abalone feeding on algae

Abalone are selective feeders, showing a preference for certain types of food, particularly red algae. Drifting algae is generally more plentiful during winter, when storms tear it loose, so the growth rate of abalone is usually greater at this time of the year.

Aquaculture

An abalone aquaculture industry in WA has been created in response to market demand. Abalone broodstock are obtained from the wild and spawned under controlled conditions in a hatchery. The planktonic larval stage lasts about 7 days, before the abalone are settled onto vertical hatchery plates. The plates are covered in encrusting green algae and microscopic diatoms as a food source for the juvenile abalone.

Fishery science

Current research is focused on stock assessment using logbook catch and effort data that forms the basis of quota setting (Total Allowable Commercial Catch) in each area of the fishery. Current research initiatives include the collection of in-water diver survey data, commercially-fished abalone shell lengths, mark-recapture data and stock enhancement/restocking research programs.

During the short recreational abalone fishing season along Perth reefs, a field survey is conducted involving DPIRD research staff, Fisheries Volunteers and university students looking to gain valuable work experience, to count the numbers of fishers on reefs and weigh their catch. Telephone surveys are used to estimate the state-wide recreational abalone catch.

Tracking the catch: Researchers weigh abalone during a Perth metro fishing session

Bibliography

Caputi, N., Jackson, G. and Pearce, A. 2014. The marine heat wave off Western Australia during the summer of 2010/11 – 2 years on. Fisheries Research Report No. 250. Department of Primary Industries and Regional Development, Western Australia.

Department of Primary Industries and Regional Development, 2016. Abalone [31 October 2018].

Department of Primary Industries and Regional Development, 2011. Marine heatwave prompts significant abalone fishing closure [31 October 2018].

Freeman, K.A. 2001, Aquaculture and related biological attributes of abalone species in Australia – a review. Fisheries Research Report No. 128, Department of Fisheries, Western Australia.

Hart, A.M., Fabris, F., Brown, J. and Caputi, N. (2013a). Biology, history and assessment of Western Australian abalone fisheries. Fisheries Research Report No. 241. Department of Fisheries, Western Australia. 96pp.

Hart, A., Strain, L., Hesp, A., Fisher, E., Webster, F., Brand-Gardner, S., and Walters, S. 2017. Marine Stewardship Council Full Assessment Report Western Australian Abalone Managed Fishery. Department of Fisheries, Western Australia, 288pp.

Hart, A. M., Strain, L. W. S., and Brown, J. Regulation dynamics of exploited and protected populations of Haliotis roei, and their response to a marine heatwave. ICES Journal of Marine Science, doi:10.1093/icesjms/fsy064

Pearce, A., Lenanton, R., Jackson, G., Moore, J., Feng, M. and Gaughan, D. 2011. The “marine heat wave” off Western Australia during the summer of 2010/11. Fisheries Research Report No. 222. Department of Fisheries, Western Australia.

Strain, L., Brown, J. and Walters, S. 2018. West Coast Roe’s Abalone Resource Status Report 2017. In: Status Reports of the Fisheries and Aquatic Resources of Western Australia 2016/17: The State of the Fisheries eds. D.J. Gaughan and K. Santoro. Department of Primary Industries and Regional Development, Western Australia. pp. 36-40

Strain, L., Fabris, F. and Walters, S. 2018. South coast greenlip/brownlip abalone resource status report 2017. In: Status Reports of the Fisheries and Aquatic Resources of Western Australia 2016/17: The State of the Fisheries eds. D.J. Gaughan and K. Santoro. Department of Primary Industries and Regional Development, Western Australia. pp. 162-166

Strain L.W.S., Brown J.M. and Hart A.M. 2019. Recovering a collapsed abalone stock through translocation. Australian Seafood CRC Project No. 2011/762. Fisheries Research Report No. 292,Department of Primary Industries and Regional Development, Western Australia. 93pp.

Western Australian Fishing Industry Council, Roe’s Abalone Fishery, http://www.wafic.org.au/fishery/roes-abalone-fishery/ [31 October 2018].

Glossary

Collapse
Reduction of a stock abundance by fishing and/or other causes to levels at which the production is negligible compared to historical levels.

Larvae
The immature form of animals which undergo metamorphosis (a change in form) before becoming an adult.

Mortality
Frequency of death.

Radula
Tongue-like feature in the mouth of certain molluscs, consisting of rows of horny teeth used to scrape food off rocks.

Settle
Change from a free-swimming form to one that attaches to a substrate.

Spat
The development stage at which shellfish larvae form shells and settle out of the water column to attach themselves to reefs or the seabed.

Spawn
Release or deposition of spermatozoa or ova, of which some will fertilise, or be fertilised, producing offspring.

Stock assessment
Process of collecting and analysing biological and statistical information to determine the changes in the abundance of fishery stocks.

Fish illustrations © R.Swainston/www.animafish.com