Commercial Fisheries of WA - Scallops
The Fishery
Several scallop species occur off the Western Australian coast, but only the Southern saucer scallop, Amusium balloti, is abundant enough to support a commercial fishery. Unlike some other scallop species, A. balloti is an active swimmer, so the scallops are trawled rather than dredged.
Scallop fisheries in WA may produce widely varying catches from year-to-year. A good price and demand are maintained for scallop meat in local and international markets.
Scallops are normally fished between March and November and the fishery is closed during the summer.
Prawn trawlers in Shark Bay are licensed to take both prawns and scallops. In general, vessels licensed for scallop fishing take approximately 70 to 80 per cent of the total catch, while the remainder is taken by prawn trawlers.
Because scallops are usually landed as meat (out of the shell), catches are commonly reported as meat weight. Whole weight is approximately five times the meat weight, depending on scallop condition.
For current and historical catches of scallops in the Shark Bay Scallop Managed Fishery, the Abrolhos Islands and Mid West Trawl Fishery, the South West Trawl Managed Fishery and the South Coast Inshore Trawl FIshery see the latest State of the Fisheries report.
Annual catches in scallop fisheries can vary enormously. An unusually strong recruitment (when many young scallops survive to fishable size) in 1990 resulted in the highest catches on record for Shark Bay; with 2,530 tonnes in 1991 and 4,144 tonnes in 1992. The catch for 1993 in Shark Bay was still high at 1,935 tonnes with between 300 and 600 tonnes considered an average annual catch.
The two main fisheries, in Shark Bay and at the Abrolhos Islands, have been fished since the late 1960s with moderate catches (up to 272 tonnes in 1969), followed by a slump in the early 1970s, when about 40 tonnes was an average annual catch.
The boats used for the scallop fishery were initially modified prawn trawlers. Catches increased considerably in the late 1970s and early 1980s due to good scallop recruitment and more efficient fishing (more boats, better gear, longer hours). Changes in processing and marketing methods also improved profitability.
Processing scallops involves 'shucking' (removing the animal from the shell) and trimming back to the white 'meat' by removing the roe sac. Until 1978, all scallops were landed whole and processed ashore, but since 1979 they are usually processed at sea and landed as high quality frozen meats.
Small quantities of scallops may be left 'roe-on' to supply the gourmet seafood market.
Biology
The major commercial species, the Southern saucer scallop, is found around a wide area of coast between Broome and Esperance where the ocean floor is sandy. It occurs in greatest numbers in Shark Bay.
In Shark Bay, spawning occurs between April and December. Most scallops from one year's spawning reach fishable size (shell size approx 90mm) by April of the following year. At this time, they are 9 - 12 months old and about to begin their first spawning season.
Further south in the scallop beds around the Abrolhos Islands, spawning occurs between August and March.
Scallops have a larval phase of 18 - 24 days, and settle to the bottom after this time. Once settled, the tiny juvenile shells are known as 'spat', a term also applied to other bivalve species such as oysters.
In WA, the Leeuwin Current carries warm water southward and influences coastal fisheries. While the relationship is not completely understood, in years when the Leeuwin Current flow is strong, scallop recruitment in Shark Bay is low, and vice versa. The effect may be caused by side-currents flushing scallop larvae out of bay.
The Southern saucer scallop can grow to 13cm in length and live up to three years.
Scallops feed on organic material which they filter from the water and are in turn eaten by pink snapper, turtles and octopus.
A nematode worm sometimes infests scallops and although it presents no danger to humans, it can lower the value by ruining the appearance of the meat in older animals. However, if scallops are caught at the optimum age (about a year old) risk of worm infestation is almost eliminated.
Marketing
Nearly all the scallop catch is exported to Asia, via the Hong Kong markets. Following low prices in 1991, blamed on poor marketing and price manipulation of buyers in Hong Kong, the scallop industry changed its approach in 1992 and prices have since improved. (Note that as selling prices of scallops on the export market are quoted in $US, exchange rate variations can affect the $A price.)
Some scallops are sold on the Australian market, but are usually considered a luxury item.
The desirable 'meat' of the scallop is the animal's adductor muscle. Other parts are usually trimmed away during processing although the white (male) or coral-coloured (female) roe sac may sometimes be left for gourmet cooking purposes.
Scallop meat is transported and marketed fresh or frozen.
Fishing Control
Although scallop recruitment is variable, at the current levels of fishing effort the stock shows no signs of over-fishing. The aim of management and industry is to ensure breeding stocks are preserved and the industry remains viable.
In the scallop fisheries, input controls are used, which means the fishing effort is restricted by various methods.
The main strategies currently used to manage scallop stocks are the maintenance of adequate spawning stocks and fishing strategies which ensure that scallops are taken at the right age for good meat weight and condition for market.
The Shark Bay fishery is closed in summer months (usually November - March). In addition, there are controls on boat and gear size and configuration, such as the number and opening width of the trawl nets and a minimum mesh size of 100mm for vessels licensed to take scallops only. Prawn vessels use smaller mesh (50mm) to take both prawns and scallops.
No minimum shell size is set for scallops, but controls on mesh size (which is set to allow juvenile scallops to pass through the nets) and limits on seasons ensure most scallops caught are larger than 90mm.
The opening date of the Shark Bay scallop season is varied according to the strength of scallop recruitment. This is determined by carrying out a pre-season survey in October/November each year. This survey also provides a basis for the reliable forecast of scallop catches for the forthcoming season in the Shark Bay fishery.
The season commencement date depends on the abundance of 'recruits' and residual scallops.
In 1983, the size of the scallop-only fishing fleet in Shark Bay was limited, pending a four-year biological study. Following the study's findings, the fishery was declared limited-entry. The original 14 boats now operate in conjunction with the 27 vessels of the Shark Bay Managed Prawn fishery.
The Abrolhos Islands scallop fishery was declared limited-entry in 1986 and 16 licensed vessels currently fish it.
In 1993, the Department of Fisheries approved 24-hour trawling for dedicated scallop boats in the Shark Bay and Abrolhos fisheries, in the interests of improved safety and fresher product. With 24-hour trawling, the catch can be processed and frozen at a steady rate, or landed when most convenient.
The geographical overlap of the scallop and prawn fisheries means that the management includes minimising interference with prawn stocks and scallop sharing resources between the dedicated scallop and prawn fleets.
A maximum limit on crew numbers (13 for scallop boats and 6 for prawners) gives the scallop boats a greater capacity for fishing effort and helps determine the catch share.
At the Abrolhos Islands, the scallop season is open to optimise product quality and meat weight. The scallop season also coincides with the Abrolhos Island Rock Lobster Fishery, which is open between 15 March and 30 June.
Research
Skippers of scallop vessels record logbook data which provides details of the daily catch and fishing effort. The fishery is mapped in smaller blocks (10 x 10 nautical miles) and catch and effort details are kept for each area fished. A high participation rate and industry cooperation makes this a valuable monitoring program.
Since 1982, pre-season surveys by the Department of Fisheries have examined the strength of scallop recruitment in Shark Bay as a guide to the following year's catch and to an appropriate opening date for the season.
The survey data allows management measures to be tailored to the expected abundance of scallops and provides a measure of recruitment strength which is independent of catch records.
Researchers are aiming for a better understanding of the wide variations in scallop recruitment (which is influenced by the Leeuwin Current and possibly other factors). Collection of satellite data on the Leeuwin Current is continuing, and temperature sensors were placed in Shark Bay in 1992 to record water temperatures as an index of the Leeuwin Current effects.
Environmental Status
Most scallops live in pristine marine environments away from human activity, though some are trawled near population centres at Fremantle, Geographe Bay and Esperance.
No adverse effect has been noted on stocks or their quality in these areas but as scallops, like all shellfish, are susceptible to pollution, any coastal development is assessed for its environmental impact.
Management of the scallop fishery is not affected by the declaration of Shark Bay World Heritage Area. The fishing areas are clearly delineated in the World Heritage Management Plan.
Future Developments
Some scallop species are being tested in hatcheries, but the Southern saucer scallop has a fragile shell which makes it unsuitable for cage-rearing. Ocean-ranching (stocking and harvesting scallops on defined areas of the sea-floor) is currently being investigated by industry.
One future prospect for the scallop fishery is a continuing variation in annual catch. Fishers must adopt fishing strategies which will cope with this variability.
In the Shark Bay fishery, a balance must be achieved between maintaining the levels of spawning stock and taking scallops before their condition deteriorates with the onset of spawning. However, at the Abrolhos the aim is to take the maximum yield available, as the scallops have finished spawning by the time the fishery starts in April.
Strategies for co-operative marketing may be needed between Western Australia and Queensland, Australia's other main source of scallops, to ensure the best prices are maintained on overseas markets.
Fishery Snapshot
- On a live-weight basis, the scallpop fishery was the largest in WA in 1991 and 1992, with most of the catch coming from Shark Bay.
- The performance of scallop fisheries can be highly variable. In the early 1990s there were record catches in Shark Bay of up to five times the usual level, but catches have now returned to normal (300 to 600 tonnes meat weight).
- Scallop and prawn fisheries overlap in Shark Bay. As a consequence, management of the fisheries must address resource-sharing and adjust fishing controls to minimise any conflict.
For an overview of the management, current and historical catch details for these fisheries please see the State of the Fisheries Report.
Glossary
| Biomass | The estimated combined weight of a fish stock (spawning biomass = weight of all mature animals). |
|---|---|
| Catch returns | Obligatory records kept by fishers giving details of their catch. |
| Demersal | Found on or near the bottom of the sea. |
| Input controls | Controls on fishing to limit catches, e.g. size of boat and gear, seasonal closures, or limiting licences. |
| Fishing effort | Amount of fishing occurring. |
| Limited entry fishery | Access to fishing grounds is limited to licenced fishers only. |
| Output controls | Controls directly limiting a catch e.g. quotas. |
| Recruitment | Movement, either by migration or growth to legal size, of juveniles into the main fished stock. |
| Roe-off | Shellfish sold with the egg-sac (roe) removed. |
| Shuck | Remove a mollusc, (abalone or scallop) from the shell. |
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