Commercial Fisheries of WA - Prawns
The Fisheries
Prawning is Western Australia's third most valuable commercial fishing industry, (after rock lobster and pearling) and is worth around $60 million annually.
Prawns are trawled in several managed fisheries off the Western Australian coast.
The number of boats working each fishery is limited, though some are permitted to fish more than one area. Currently, up to 117 trawlers may fish for prawns in the various prawn fisheries in WA. In the Shark Bay prawn fishery, scallops also provide a valuable additional catch.
There have been small subsistence prawn fisheries around Perth and the Peel Inlet since settlement in 1829, but serious commercial prawning did not begin in WA until the early 1960s.
The commercial prawning industry in WA takes a variety of species, primarily the western king prawn (Penaeus latisulcatus), brown tiger prawn (P. esculentus), banana prawn (P. merguiensis) and blue endeavour prawn (Metapenaeus endeavouri). Trawlers also take a range of other marine species as an incidental catch, such as crabs, Moreton Bay bugs and squid.
The five main prawn fisheries in WA vary in the proportion of species taken and times of operation during the year.
Catches of prawns can be highly variable, due to environmental factors such as water temperatures, cyclones, and broad-scale oceanographic features. Careful management of the fishing effort has ensured that breeding stocks are maintained, which assists in maintaining stable prawn stocks and catches.
Management of the prawning industry in Western Australia is complex and arrangements can vary annually, to maintain breeding stocks and to optimise the value of the catch from each fishery.
Management aims include sustaining prawn stocks and maintaining economic viability.
Currently, management priority is on the tiger prawn stocks which are vulnerable to overfishing in multi-species fisheries. However, the mainstay of the Exmouth Gulf and Shark Bay prawn fisheries is the king prawn, which is caught in greatest quantity.
The total annual prawn catch for Shark Bay and Exmouth Gulf prawn fisheries can be found within the State of the Fisheries Report.
Biology
Prawns mature at about 10-12 months of age and spawning occurs in offshore waters. In Exmouth Gulf and Shark Bay, larvae drift shoreward to shallow, hypersaline waters. Here, the juveniles develop until physiological changes demand they move back to oceanic waters to spawn, completing their life cycle. At the end of this migration of juvenile prawns, the prawns enter the trawl grounds where they can first be caught commercially. These areas are generally offshore, in water 10-30 metres deep.
Prawns are active mainly at night, remaining buried in the sea-bed during the day. In winter, lower seawater temperatures slow their metabolism. Consequently prawns do not require as much food, and forage less, so they are less vulnerable to trawling, resulting in lower catches. Weather conditions can reduce the annual catch of one species and increase the annual catch of another. Catches of banana prawns are increased by the rainfall from cyclones, but this may reduce catches of tiger prawns.
Prawns, like other crustaceans, moult their shells during growth. This usually occurs around full moon. Feeding varies during the various stages of the moult cycle, with prawns ceasing to feed around the time of the moult. This results in prawns being less catchable at times of full moon. Also, because prawns have soft shells after the moult, catching soon after the full moon can lead to a high proportion of soft and broken prawns in the catch. When fisheries managers determine opening dates of prawning seasons, these factors are taken into account.
The catch is affected by each species' behaviour. Schools (called ‘boils') of banana prawns are caught mostly during the day close to the water's surface. King prawns burrow deeper into harder substrates and are more affected by light than tiger prawns. Tiger prawns burrow in soft substrate and are more easily caught by trawling than king prawns. Both these species are trawled during the night.
The Seven Fisheries
Shark Bay Prawn Managed Fishery
The Shark Bay Prawn Managed Fishery is bounded by the Ningaloo Marine Park in the north and a point just below Zuytdorp Point in the south, including waters within Shark Bay below this latitude. Large areas of the fishery, particularly inshore, are closed to trawling to protect sensitive habitats and juvenile prawns. King prawns are the dominant species, being about 65 per cent of the catch. Tiger prawns make up the rest. The 27 boats in the fishery also trawl for scallops and take between 20 and 30 per cent of the annual scallop catch in Shark Bay.
Historical prawn catches for the Shark Bay Prawn Managed Fishery can be found within the State of the Fisheries Report.
Exmouth Gulf Prawn Managed Fishery
This highly productive but variable fishery operates in the Exmouth Gulf. Initially banana prawns were fished, but since 1965, king and tiger prawns have been the mainstay of the Exmouth Gulf catch.
In the early 1980s, tiger prawn stocks in Exmouth Gulf declined due to heavy fishing pressure, with the average annual catch falling from about 600 tonnes in 1975 to less than 100 tonnes in 1983. Stringent management measures were introduced with industry cooperation and tiger prawn catches have returned to the 300 - 500 tonnes range.
The king prawn stock has remained stable since 1970. During the 1970s the average annual catch was around 200 - 300 tonnes. In the early 1980s, management measures reduced effort on tiger prawn stocks, causing more effort to be shifted to the king prawn stock. As a result, the king prawn annual catch has grown to an average of 456 tonnes.
Endeavour prawn catches remained stable up to 1999 with a five-year average of 188 tonnes. However, due to intense cyclone activity in early 1999, the catch of endeavours reached an all-time high of 543 tonnes.
Due to a series of industry-funded buy-back schemes and gear modifications, the number of boats operating in the Exmouth Gulf fishery has fallen from 23 to 12.
Historical prawn catches for the Exmouth Gulf Prawn Managed Fishery can be found within the State of the Fisheries Report.
Nickol Bay Prawn Managed Fishery
This fishery extends from Dampier to the southern end of Eighty Mile Beach (between 116°45'E longitude and 120°E longitude and on the landward side of the 200 metre isobath). The major fishing area lies off Nickol Bay itself. Fourteen trawlers are licensed to operate in this fishery.
Production is highly variable because the dominant catch species, banana prawns, is rainfall dependant. Conditions appear to be favourable for this species when rainfall is high during December to March inclusive.
Historical prawn catches for the Nickol Bay Prawn Managed Fishery can be found within the State of the Fisheries Report.
Since the catch is highly variable, most Nickol Bay operators have multiple endorsements on their licences which entitle them to fish for prawns and other species (such as scallops) in other managed fisheries.
Onslow Prawn Managed Fishery
Divided into three zones off the coast near Onslow, this fishery harvests mainly tiger prawns from inshore areas, with a lesser catch of king, banana and endeavour prawns further offshore.
The catch is affected by similar environmental factors to those influencing Exmouth Gulf and the success of tiger prawn breeding stock management.
Historical prawn catches for the Onslow Prawn Managed Fishery can be found within the State of the Fisheries Report.
Environmental factors can also vary catch composition in this fishery: high rainfall years may result in a decline of the tiger prawn catch and a corresponding increase in the banana prawn catch.
Onslow Prawn Managed Fishery Onslow, gazetted in 1991, was the last prawn fishery to be declared a managed fishery in WA.
Kimberley Prawn Managed Fishery
The Kimberley fishery operates off the north-west coast of WA between Koolan Island and Cape Londonderry (east of 123°45'E longitude and west of 126°58'E longitude).
It is open to trawlers specifically licensed for the Kimberley fishery, many of which are also licensed for Shark Bay, Nickol Bay or Exmouth Gulf prawn fisheries as well as a number of vessels which operate in the Northern Prawn Fishery (NPF). However, most of these trawlers find other grounds more attractive so production from this fishery is light and sporadic. Banana prawns make up the majority of the annual catch.
Historical prawn catches for the Kimberley Prawn Managed Fishery can be found within the State of the Fisheries Report.
Broome Prawn Managed Fishery
A small area off the coast of Broome is also trawled for king and coral prawns with catches averaging 83 tonnes and 52 tonnes respectively per year. Trawling in the area is restricted to five vessels which fish for six to eight weeks during June and July each year.
The boats licenced for the Northern Prawn Fishery (NPF) trawl this fishery while the NPF is closed. (The NPF is a Commonwealth fishery extending across the top of Australia. Boats from WA, NT and Qld operate in its waters).
Southern Fisheries
Some prawns are taken near Port Gregory, as part of operations in the Abrolhos Islands and Mid-West Trawl Managed Fishery. It is seasonal, sporadic, low-value and restricted so as not to affect the west coast rock lobster fishery.
Three trawlers operate off Mandurah, south of Perth, and the small, high-grade catch of king prawns is landed fresh to supply metropolitan restaurants and retailers.
Markets
The catch is either processed at sea, frozen in 12kg boxes, or placed in refrigerated sea water then landed for factory processing. Most large king and tiger prawns are exported to Japan, Europe and Asia (whole or headless in 1.5kg, 2kg or 3kg boxes) as a valuable commodity, whereas Australian markets take most of the smaller king prawns (cooked or fresh).
Smaller grades of prawns are now facing competition on the international export market from aquacultured prawns grown in the Philippines, Vietnam, Malaysia, Thailand, Taiwan, Ecuador and the Gulf of Mexico.
Emphasis is likely to stay on developing the markets for larger, more valuable prawns. Prawn aquaculture is currently not highly developed in Australia.
Fishing Management
Because the Western Australian prawning industry did not really develop until the late 1960s, the Department of Fisheries researchers and managers were able to develop and implement a variety of fishing controls and modern management measures for it to ensure prawn stocks were not over-fished. These controls aimed at safeguarding the long-term sustainability of prawn stocks, improving quality, and working with industry members to maintain high economic returns from these fisheries.
Fishing controls employed in managing the prawn fisheries include:
- Seasonal closures (prawns are normally fished between March and November, with fishing closed during Summer).
- Temporary closures of some areas within each fishery to protect spawning stocks and increase the proportion of larger export grade prawns in the catch.
- Nursery areas in which trawling is banned to protect habitat.
- Limiting vessel numbers and licences.
- Trawl gear and vessel restrictions (covering vessel size, net head-rope lengths and mesh size specifications).
A number of buy-back schemes have operated in Exmouth, Shark Bay and Onslow. These schemes have removed boats from these fisheries, with part of the licence fees for boats which remain in the fishery going towards the purchase and cancellation of licences.
‘Moon closures' in Shark Bay and Exmouth Gulf involve closing the fishery for three to ten nights around the full moon. The closures reduce the proportion of soft, newly-moulted prawns in the catch and improves the efficiency of the fleet. Other benefits are improved vessel maintenance and a better social or family life for crews.
Recreational Fishing
Recreational prawning is generally confined to rivers and estuaries in the South West region. The most popular areas include the Swan and Canning Rivers near Perth and the Peel Inlet near Mandurah.
The western school prawn and western king prawn are the main species taken between November and June. The total quantity of prawns caught each year by recreational fishers cannot yet be reliably estimated.
Information on the daily bag limit per person is available from here.
There are controls on size and method of fishing and seasonal closures may be imposed on certain areas. Recreational fishers cannot sell their prawn catch.
Research
Commercial prawners must submit details of their monthly catches to the Department of Fisheries. In a separate research program, fishers using purpose-designed logbooks also record daily catch, effort and location information. A high participation rate and industry cooperation makes this a valuable monitoring program.
Surveys of recruitment (March-April) and spawning stocks (August-October) by the Department of Fisheries research staff provide checks on the health of prawn stocks.
To address the issue of bycatch (marine species discarded by fishers), the Department of Fisheries and the fishing industry conducted a two-year research project designed to reduce bycatch taken by trawlers. Finance was provided from the Natural Heritage Trust, the Development and Better Interest Fund and industry funding.
To enable future planning, research is needed into the relationship between marketing changes and fleet dynamics, as the patterns of fishing effort may change according to the product demanded by the market.
A recent shift in marketing requirements has meant fishers are targeting larger sizes of prawns. This has had the effect of reducing overall annual tonnage caught from the fishery but may increase its value.
Further studies of environmentally-driven changes in recruitment, such as the effects of the Leeuwin Current and tide cycles may prove useful in making future catch predictions.
Environmental Status
The remoteness of WA's prawn fisheries has minimised the effects of human activity and coastal development on their environment and the industry enjoys a valuable international reputation for high-quality seafood from a pristine environment.
Future Management
The aim of management by the Department of Fisheries is to improve operating efficiency and profitability, whilst protecting prawn stocks and maintaining sustainability and ecosystem health.
The viability of the prawn fishery depends on a well-defined market niche for larger grades of prawns, which are presently free from any international aquaculture competition.
In managing the fishery it is necessary to find a balance between delaying fishing to target larger, more valuable prawns, and the loss of prawns to natural mortality. Achieving the optimal balance gives the highest value for the fishery.
Fishery Snapshot
- Various prawn species, mainly tiger, king and banana prawns, are harvested along WA's northern coast, with recreational prawn fishing in southern estuaries.
- Prawning is Western Australia's third most valuable export fishery.
- Because serious commercial fishing did not begin until the 1960s, controlled expansion and careful monitoring of prawn stocks were possible.
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 | Fishing activity occurring in a fishery |
| Gear units | A standard measure used to manage fisheries, (e.g. 1 gear unit = 10 metres of net) varying as needed |
| Limited entry fishery | Access to fishing grounds is limited to licensed fishers only |
| Recruitment | Movement, either by migration or growth to legal size, of juveniles into the main fished stock |
| Trawling | A variety of fishing operations in which nets are towed behind a boat. They may be set to fish bottom, middle or surface waters, depending on the target species |
| Year-Class | Fish spawned in the same season |
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