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State of the Environment Australia
Australia State of the Environment Report 2001 (Theme Report)
Australian State of the Environment Committee
Authors, CSIRO Publishing on behalf of the Department of the Environment and Heritage
© Commonwealth of Australia 2001, ISBN 0 643 06751 5
Fishing activities have impacts well beyond the main target species and include the effects on ecologically related species and on marine ecosystems. In recent years, the effects on other fish species have been the major issue, but the emphasis is now changing to the effects on ecosystems.
The components of fishing bycatch can be described as:
In most fisheries non-target species may be retained. When there is a commercial market for them, this is described as byproduct and can comprise a significant proportion of a catch in some fisheries. Indigenous people who catch only what can be used are especially concerned about bycatch as a waste of resources.
There is very limited information on the non-target catch in many Commonwealth fisheries (Caton and McLoughlin 2000). Recording of bycatch is difficult because there is a need for a high level of taxonomic skills to reliably identify the organisms and because of a lack of skilled observers. The Commonwealth Sub-Antarctic Fisheries have perhaps the most extensive observer coverage.
The Northern Prawn Fishery was one of the first to introduce compulsory logbooks that were completed by fishers and cross-checked by processors. In 1995 it became compulsory for fishers to record the retained catch of non-target species and turtles.
In the far northern Great Barrier Reef Marine Park, for every tonne of prawns harvested, about six to ten tonnes of other species are discarded. A study on the environmental effects of prawn trawling (Poiner et al. 1998) found that about one-third of bycatch species were crustaceans and two-thirds fish.
Some State-managed fisheries record some non-target species, mainly byproduct and vulnerable species (e.g. turtles and marine mammals), but discards of the majority of non-target species are not recorded.
Trawling is one of the most widely used commercial fishing methods in Australia, with demersal trawling being the major technique. There are trawl fisheries for fish, scallops, scampi, prawns, and other seafood. The nature of the catch in trawl fisheries can include threatened species and invertebrate and other species.
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| Commercial prawn trawl fishing on the Great Barrier Reef is important to the Australian economy. |
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Source: A Elliot, Great Barrier Reef Marine Park Authority.
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Because demersal trawling and shellfish dredging makes contact with the seafloor, it can have substantial impacts on seabed habitats and benthic ecosystems (Harris and Ward 1999). The extent of essentially indiscriminate impacts can be significant, including physical removal of organisms and non-living components and increases in water turbidity. Impacts arise from the removal of target and non-target species and the removal and disturbance of invertebrate species and associated benthic habitat. Repeated trawling may prevent the recolonisation of benthic species, both sedentary and mobile.
CSIRO and the Queensland Department of Primary Industries completed a five-year study of the environmental effects of prawn trawling in 1996 (Poiner et al. 1998). The study area covered 10 000 km2 in the far northern Great Barrier Reef Marine Park. The research showed that each pass of a trawl along the seabed removes about 5 to 25% of the seabed life. However, there is a cumulative effect; seven trawls over the same area of seabed removed about half of the seabed life, and 13 trawls removed 70 to 90%. Different species have different levels of vulnerability. Large sponges, for example, are particularly susceptible to trawling.
A few deep seabed sites have been studied, such as on the North West Shelf and on the continental shelf adjacent to the Great Barrier Reef. However, there is relatively little understanding of benthic communities in Australian waters. Seamounts are trawled for Orange Roughy, and some have been damaged by this activity. Seamounts are sites of highly valued marine biodiversity (see Seamounts).
Coastal habitat especially estuaries are nursery grounds for the juveniles of fish species. These habitats include seagrass beds, saltmarshes and mangroves and other coastal wetlands. Habitat loss or degradation may also result from land-based activities that cause nutrient enrichment, pollution from pesticides, or sedimentation (see sedimentation).
Some States are actively addressing the protection or rehabilitation of inshore habitats. For example, in 1995 New South Wales Fisheries introduced Fish Habitat Protection Plans to facilitate habitat protection on a State, regional or local scale or for particular communities or species (Smith and Pollard 1998). The second protection plan was gazetted in 1997 and applies specifically to seagrass habitats.
Fisheries Western Australia is developing a series of Fisheries Environmental Management Reviews for each of the main regions of Western Australia to, among other things, identify habitats of importance for fisheries. Each Environmental Management Review is to be supported by a Management Plan that will develop and implement responses to the issues identified in the Reviews.
Coasts and Oceans Theme Report
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Australia State of the Environment 2001 Report
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