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Non-Target Species
- Introduction
- Sources of information
- Catch, composition and fate
- Species of public concern
- Interactions between fisheries
- Wastage
- Ecological effects
- Assessments of the effects of fishing
Introduction
Fishing not only harvests species that are sought by fishers, but also significantly affects species that are not sought or wanted. We use the term non-target species for those species (including fish, sharks, crustaceans, molluscs, marine mammals and reptiles) that are unintentionally taken by the fishery or are not routinely assessed for fisheries management. The term usually relates to an entire fishery and its management and not to the targeted fishing activities of individual fishers. The non-target species can also be classified as bycatch or by-product. By-product are species that have market value and tend to be retained and sold by fishers, while bycatch are discarded.
Commonwealth fisheries management requires that fisheries resources are exploited with regard for the effect of fishing on non-target species. What needs to be done in order to satisfy this requirement is becoming clearer but there is little empirical evidence or applicable theory to address the relevant questions.
The 1999 BRS report Non-Target Species in Australia’s Commonwealth Fisheries examines the information available on non-target species in Commonwealth fisheries—the amount and composition of the catch, the fishery-specific issues, previous assessments of fishing effects, and assessments required in the future.
Sources of information
Current understanding of the effects of fishing on ‘non-target’ species in Commonwealth fisheries comes from several sources of information: onboard monitoring of commercial vessels by scientists and observers; systematic fishery surveys; commercial and exploratory surveys; catch logbooks and dockets filled out by fishers; information from adjacent fisheries; and anecdotal reports. Logbooks are often an incomplete source of information since they mainly record the retained catch and do not adequately record the non-target species which are often discarded. The most comprehensive and reliable sources have been onboard monitoring and scientific fishery surveys explicitly aimed to record non-target species.
Catch, composition and fate
Though it is possible to obtain a qualitative indication of the composition of the catch, there is insufficient quantitative information to be confident of the actual amount and composition of the non-target catch in most fisheries (See Table below). Exceptions are the main prawn (Northern Prawn Fishery, Torres Strait Fishery) and fish trawl (South East Fishery) fisheries, and the longline tuna fisheries ( Eastern Tuna and Billfish and Southern Bluefin Tuna). Overall, the available information on non-target catch and composition could best be described as snapshots of some fisheries.
Much of the non-target catch is discarded, particularly in trawl fisheries. The proportion discarded is largest in the major prawn and fish trawl fisheries. Fisheries such as the squid jig and purse seine fisheries are highly selective and have little non-target catch and almost no discards. Even within a trawl fishery, however, the level of discarding can vary greatly by region, season and fishing operation. In the tropical prawn fisheries, discards are rapidly eaten by birds, dolphins, sharks and bottom scavenger fishes. We do not know the fate of the discards in other fisheries and it will be different to that observed in tropical prawn fisheries.
Species of public concern
In most Commonwealth fisheries there are non-target species caught that are considered vulnerable to fishing, raise public concern or are protected by legislation, e.g. listed under the EPBC Act public. To date species of most concern have been albatrosses in southern waters and turtles in northern tropical waters. There are several other species such as sharks, sawfishes, seabirds, sea snakes and seahorses that are listed have been nominated as vulnerable or endangered in various national or international forums. All marine mammals are protected under the EPBC Act. Dolphins and whales rarely interact with Commonwealth fisheries, however, seals are incidentally caught in several southern Commonwealth fisheries. Interactions with these species are discussed in the listed and threatened species and fisheries interactions section.
Generally, there is rarely sufficient information on the incidental catch of species of public concern to quantify the fishery mortality and determine the impact of fishing on their populations. This is driven by the fact observer coverage is generally required and these are usually rare events. In the main, listed species have been identified in response to national or international concerns as to the status of their populations. There is now positive action being taken in Commonwealth fisheries to assess the vulnerability of the non-target species taken in their catch, and research projects and observer programs have been put in place to assess and quantify the effect of fishing on species of public concern.
Interactions between fisheries
Interactions arise between fisheries when the non-target species of a fishery is the target species of another fishery. They complicate the assessment and management of a fishery and can lead to tension between fishers. Factual information on the catch and an accurate assessment of impact can define the problem, identify solutions and significantly reduce this tension.
Significant fishery interactions occur in about half of the Commonwealth fisheries. They are more pronounced in the more populous Southern and Eastern part of Australia where several Commonwealth fisheries occupy common areas or are adjacent to important State fisheries.
Wastage
The wastage of fishery resources as a result of discarding has drawn significant attention nationally and internationally. The perception of waste has adverse societal and economic implications. It has been defined as the difference between potential and actual contribution of those resources to the well-being of a nation. Ecologically the term ‘waste’ is largely meaningless since the biological matter discarded may be quickly recycled.
In the BRS 1999 study, between 47 000 t and 89 000 t of ‘non-target’ catch was estimated to be discarded annually in eight of Australia’s Commonwealth fisheries for which there is reasonably reliable information. These eight fisheries land about 61 000 t of catch worth over A$320 million.
Waste is of most concern in the two major Commonwealth trawl fisheries - the Northern Prawn Fishery and the South East Trawl Fishery that together account for about 85% of the known discards. In the Northern Prawn Fishery, a study in the late 1980s found that logistic, processing and marketing difficulties made greater use of the ‘non-target’ catch uneconomic. Currently the emphasis is largely on reducing the discards through the use of bycatch reduction devices (BRDs) leaving changing market preferences to increase the level of utilisation over time. In the South East Trawl Fishery, there is increasing focus on the reduction of discards of non-target species.
Ecological effects
Ecological effects of fishing may include changes within a marine animal community due to the removal of predators, prey or competitors, changes mediated through the disturbance of the sea-bottom or habitat, and changes resulting from additional ‘artificial’ food sources. These direct sea-bottom or habitat effects are mainly associated with demersal trawling.
The ecological effects of fishing also have to be examined in fisheries that are highly selective such as purse seining. The question is increasingly being asked if a large catch of only one species has a more pronounced ecological effect on a marine animal community than a similar catch spread across many species.
The process of strategic assessment of fisheries under the EPBC Act requires all fisheries to consider the potential ecosystem and habitat impacts of their activities. Ecological risk assessment processes are being implement to identify high risk fisheries and ecosystem components. This is discussed in more detail in the EBPC Act section.
Assessments of the effects of fishing
There are few comprehensive assessments of the effects of fishing in Commonwealth fisheries. Substantial decreases in the populations of some species of albatross have been strongly linked to the global longline fishery. In Australian waters a threat abatement plan that cooperatively involves the fishing industry is in place. The extent that declines of turtle populations are the direct result of prawn trawling in Northern Australia is less certain since there are numerous other sources of mortality, many of which are unquantified. Modelling studies of Australian turtle populations highlight the importance of properly identifying and comparing fishing and non-fishing sources of mortality in assessments.
Short and long term changes in the abundance of non-target species communities in the Northern Prawn Fishery have been attributed to the fishing activities of prawn trawlers as well as environmental changes in local conditions. Similar long term changes in non-target species abundance are under investigation in the South East Trawl Fishery. Separating out the effect of fishing from other environmental effects can be difficult where information is limited to fishery independent surveys interspersed by long periods of time. Adaptive management that opens and closes fishing grounds and controlled fishery experiments to monitor fishing impact and recovery within small representative areas provide more powerful assessments of the actual effect of fishing. None of these approaches are currently being undertaken in Commonwealth fisheries. An issue across Commonwealth fisheries is the extent that inferences can be made of the ecological impact of fishing upon the integrity of entire animal assemblages and the ecosystem as a whole. As yet, there are no studies that have examined this issue.
Basic information on the non-target catch is still largely lacking in many Commonwealth fisheries. It seems unlikely that the management of a fishery can ‘have regard to the effects of fishing on ‘non-target’ species...’ without a methodical approach to examining what and how much is taken by the fishery. The most direct and effective method is through onboard monitoring of commercial vessels by observers or scientific personnel. Not all Commonwealth fisheries need to be monitored continuously. Some fisheries may only require baseline information for future comparison, others occasional or regular monitoring spaced by periods of 3 to 5 years. These should be preceded by smaller pilot projects that examine the logistics and methods particular to the fishery. There is also an important role for the use of cooperative fishers in collecting onboard information on species that occur rarely in the catch. The coverage of fishing activity required to reliably estimate the catch and mortality of rare species makes monitoring by observers or scientists prohibitively expensive.
The process of strategic assessment of fisheries under the EPBC Act requires all fisheries to consider the potential non-target, ecosystem and habitat impacts of their activities. Substantial on-going research is focused on Ecological Risk Assessment Processes to try and deal with the limited data and the broad array of non-target species and ecosystem effects. This is discussed in more detail in the EBPC Act section. These risk assessments should provide focus for activities to mitigate impacts on non-target species and ecosystem components.
The Commonwealth Policy on Bycatch incorporates the views of a wide range of public, industry, government and non-government stakeholders. It sets the guiding principles and objectives to address non-target species issues across Commonwealth fisheries. Under the policy individual fisheries have to develop fishery-specific bycatch actions plans. These are discussed in more detail in the Bycatch Policies section.
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