FAQ

Which WA commercial fisheries capture prawns and how are they caught?

Prawns are captured using trawl nets in a small area adjacent Fremantle, Port Gregory, Shark Bay, Exmouth Gulf, Nickol Bay, Onslow and north of Broome in specific areas. Prawns are also captured by one operator in the Peel/Harvey Estuaries in Mandurah using beam tide trawl nets. There are strict controls on the number and size of boats, the size of nets, and the area and times of operation.

What steps are being taken by trawl fisheries to reduce bycatch (non target species)?

Firstly, the areas trawled are limited to areas of high prawn abundance and relatively low bycatch abundance. Secondly, the time allowed for trawling is restricted to times of high prawn abundance. Thirdly, it is compulsory in most WA trawl fisheries to use Bycatch Reduction Device's (BRD's) which are a modification to fishing gear to reduce the catch or kill of non target species during fishing operations, ie Turtle Exclusion Devices (TED's) or Fish Exclusion Devices (FED's). TEDs are compulsory in all prawn fisheries. FEDs are being trialled (compulsory in one net mainly to ensure the integrity of catch data over time) in Shark Bay, Exmouth Gulf, Nickol Bay and Onslow. TEDs effectively exclude all macro fauna (sharks, rays, large fish and turtles). FEDs exclude a significant part of the remaining bycatch and lose up to 12% of the expected prawn catch. Some trawl fisheries have voluntarily installed hoppers (tubs) which are fixed to vessels and keep bycatch (and prawns) submerged and alive while sorting.

What impact does trawling have on the seafloor?

Prawn nets are designed to “fly” just above the sea floor. They are kept open by otter boards that touch the bottom. Traditionally the otter boards travel at an angle to the direction of movement to spread the net mouth open but in recent years regulatory agencies have allowed the industry to use hydrofoil shapes that spread the net while moving parallel to the direction of the net. This has greatly reduced disturbance of the seafloor by the otter boards. A “tickler chain” runs ahead of the bottom leading edge of the net and bounces along the ocean floor. This excites the prawns up into the water column where they are scooped up by the net. The total spread of the two nets behind most trawlers is less than the length of a cricket pitch. This reduces during the trawl (30 – 60 mins) as the weight of the catch in the back of the net (cod end) pulls the two otter boards closer together.

How are the trawl fisheries managed and are they sustainable?

WA's trawl fisheries are extremely tightly managed with a suite of management tools in place. Almost all trawl fisheries have a restricted fishing area of operation and often, area closures apply within the restricted area of operation. All trawl fisheries have a fishing season which can be shortened during operations in response to species abundance. For example the 2003 Shark Bay prawn season lasted for 169 nights of 15 hours duration. It is anticipated that the 2004 Shark Bay prawn season will be 174 nights of 15 hours duration. It cannot be more but it can be less if the industry decides to cease fishing at any time.

The Shark Bay and Exmouth Gulf prawn fisheries have real time management where trawling areas are closed and fishing stops in response to real time catch monitoring and surveys. The industry imposes restrictions over and above the restrictions required for sustainability in order to maximize returns. The industry seeks to catch only marketable size and species of prawns in the most efficient manner possible. The industry will voluntarily close areas where prawns are less than ideal size or close a fishery when catch rates fall to lower than target levels.

All WA trawl fisheries are fitted with Vessel Monitoring Systems (VMS) which allows the Department of Fisheries to remotely monitor where trawlers are operating by satellite tracking. The tracking is extremely accurate. There are also strict rules on the type of trawl gear that can be used, and controls on the boat size and power. It is compulsory for most trawl fisheries to have bycatch reduction devices fitted into their trawl nets. In Shark Bay there are also limits on the number of crew permitted on each trawler.

Does prawn trawling in Shark Bay have an impact on Pink Snapper stocks?

There are at least three pink snapper sub-species in Shark Bay. The three pink snapper sub-species are reproductively isolated and do not contribute to each other’s populations. The two pink snapper sub-species in Shark Bay that have suffered the greatest population declines (Eastern Gulf and Freycinet Inlet) do not have, and never have had, any interaction with the Shark Bay trawl fisheries. Trawlers have never worked within the range of these sub-species.

The Shark Bay trawl fisheries have always had interaction with oceanic stock. It is thought that the oceanic stock occasionally contribute to the resident snapper population of the Western Gulf.

In 2003 it was announced that the oceanic stock was depleted (about 30% of original biomass) as a result of the bycatch or undersize mortality. Snapper quota holders agreed to a 40% reduction to their quota. The prawn trawl industry is a quota holder in that fishery. It responded by voluntarily foregoing its entire quota of snapper for at least two years and closing all areas of trawling where snapper interactions were thought to occur.

Another study completed in 2003 concluded that trawl interaction with juvenile snapper in the Western Gulf caused approximately the same mortality to the adult snapper population as the mortality arising from amateur fishers returning undersize snapper to waters of the Western Gulf. The prawn trawl industry had already voluntarily closed much of the area (and closed the Western Gulf fishery a month early). The prawn trawl industry agreed to the study’s recommendation to close a major portion of the Western Gulf to trawling. The prawn trawl industry went further and volunteered to close another area of high juvenile snapper abundance that was identified around Withnell Point.

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