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Sustainability targets for integrated management of freshwater fish resources in the face of data uncertainty

Peter C. Gehrke

Research Director, Rivers and Estuaries, CSIRO Land and Water in Brisbane.
CSIRO Land and Water, 120 Meiers Road, Indooroopilly, QLD 4068.
Email peter.gehrke@csiro.au.

[At the time of the Workshop, Peter was employed in the NSW Fisheries Office of Conservation, Port Stephens Fisheries Centre in Nelson Bay, NSW.]

Abstract

Australia’s freshwater fish resources are nationally in a state of decline. The severity of decline ranges from serious to unknown in different regions.

To sustain Australia’s freshwater fisheries the fish resources need to be rejuvenated – not merely protected – and the ecological processes on which fish populations depend need to be rebuilt. Because of the complexity of interactions between species and between different trophic levels, managing fish stocks using targets based on the sustainability of individual species is unlikely to ever achieve ecologically sustainable development of a fishery. Whilst setting targets for recovery or rebuilding can be problematic, the adaptive management approach allows a trajectory of recovery to be defined, with performance criteria assessed by scientific monitoring programs.

Freshwater reserves have potential to provide large-scale spatial and temporal refuges from exploitation and environmental degradation, without the need for accurate stock assessment data and models. Future data requirements include indicators of ecosystem condition with fish indicators derived from recreational fisheries, commercial fisheries and independent surveys.

The outlook for sustainability of freshwater fisheries is uncertain. The concept of restoring or rebuilding an ecosystem involves the assumption that processes of decline are reversible, and that a system will revert to its previous condition once the threatening processes are removed. However, this assumption needs to be validated. The success of rebuilding is likely to be dependent on the level of commitment to adaptive management.

Introduction

Rivers have been identified as perhaps the most endangered ecosystems on a global scale, because of the way they are exploited for human water supply, agriculture, industry, water storage, power generation, and harvesting of biological resources. Harvest fisheries typically have low commercial value compared to other river-based industries, with the result that the environmental requirements for sustainable freshwater fisheries often receive low priority in political decision-making processes (Welcomme 2001). The sustainability of freshwater fisheries is therefore strongly determined by decision-making influences beyond the realm of fisheries management.

In this paper I attempt to identify targets for the long-term sustainability of Australia's freshwater fish resources by discussing their status at national level.

Status of freshwater fish resource sectors

Freshwater fish resource sectors can be divided conveniently into anthropocentric sectors focussing on commercial, recreational and indigenous uses, and ecocentric sectors emphasising conservation-based and public ownership uses. Each sector is likely to have different understandings of the concept of sustainability.

To establish realistic sustainability targets for fisheries based on native freshwater fish species it is necessary to consider the national status of the resource. An informal survey of with fishery scientists from each State or Territory jurisdiction provided the overview that in the eastern mainland of Australia the native fish resource is either in a state of serious and continuous decline, or had undergone a decline previously but is stable (Table 1). In Tasmania, South Australia and the south west of Western Australia, decline is also apparent but less of a concern, whilst in the remainder of Western Australia and the Northern Territory, freshwater fish resources are thought to be in good condition. Considering the plight of freshwater systems throughout Australia, and the limited knowledge of the interrelationships between fish and other components of freshwater ecosystems (Kearney 1997), these assessments may be optimistic. The Australian Society for Fish Biology recognises that over one-third of our freshwater fish species are threatened, with additional species known to have suffered declines but which do not meet the Society's criteria for listing. At a national level therefore, it appears that freshwater fish resources are declining and this decline ranges from serious to unknown. This conclusion is supported by published studies including those by Harris and Gehrke (1997) at State level, and Kearney (1997) at national level.

Table 1. Stress status of freshwater fishery sectors by State or Territory jurisdiction. Black cells: seriously stressed and declining; dark grey cells: stressed but stable; light grey cells: little stress or in good condition. Empty cells indicate a non-existent sector in that jurisdiction. SE: south east; N: north; SW: south west. (informal survey of freshwater fishery scientists in each jurisdiction)

Sector	Qld		NSW	ACT	Vic	Tas	SA	WA		NT
	SE	N						SW	N
Commercial
Recreational
Conservation

Rebuilding ecosystems: the key to sustainable freshwater fisheries

It is clear that existing uses of fish and freshwater ecosystems are not conserving, enhancing, nor maintaining the ecological processes that support fish production, and do not therefore meet the objectives of ecologically sustainable development (ESD). Maintaining existing levels of use will not arrest the decline of individual species, irrespective of whether species are recognised as threatened or not. Nor will it reduce the major threats posed by habitat degradation, poor water quality, altered river flows, barriers to migration, introduced species and harvest fisheries (Kearney 1997).

The goals for sustainability of freshwater fish resources are strongly influenced by the temporal perspective adopted. Short-term sustainability targets over several years tend to focus on maintaining the status quo, which in Australian freshwater systems equates to continued ecological decline and eventual socio-economic deterioration. In contrast, long-term sustainability of freshwater resources over decades requires current ecosystem declines to be arrested and reversed, with a re-structuring of harvest strategies to provide for true ecological sustainability and socio-economic well-being. Simply maintaining the status quo fails ESD objectives on social, economic and ecological levels. Therefore, to sustain the interests of Australia’s freshwater fish sectors, fish resources need to be rejuvenated, not merely protected, and the ecological processes on which fish populations depend need to be rebuilt.

Targets for rebuilding freshwater systems

Following the decision to rebuild or restore an ecosystem the question arises of to which previous condition is the system to be restored. Setting the target condition under such circumstances can be highly problematic because numerous target conditions can be proposed and defended with equal vigour. Examples may range from a documented historical condition that existed before some recent disturbance, to a presumed condition prior to major disturbance – such as completion of a dam or large-scale catchment clearing – or to some earlier condition that pre-dates the arrival of European settlers in Australia. In contrast to such temporal targets, spatially-derived targets based on the best existing condition of a large number of catchments rely on the assumption that the best existing condition is not also seriously degraded. Any of these targets may have practical drawbacks that make them unachievable, but they share the common assumption that the key to future sustainability lies in the ability to revert to a previous condition. This assumption is central to the 'Back to the Future' concept of Pitcher and Pauly (1998). Alternative sustainability solutions may be proposed, but the philosophy that humans can design natural systems that are better than those that existed in the past involves a high level of risk and uncertainty as to the possible outcomes.

Rather than attempting to reach agreement on fixed targets for system rebuilding, it may be more practical to seek stakeholder agreement on the direction in which the system is to be managed, with achievable performance measures at various points in the agreed direction. Thus the trajectory of recovery becomes the target for sustainability instead of fixed targets that may give rise to dispute. Examples of trajectories that provide practical targets include:

• reduce abundance or impacts of pest fish;
• increase proportion of native fish;
• increase populations of threatened species;
• increase trophic complexity;
• increase size or value of catch;
• increase recreational catch; and
• return to defined historical condition.

Although the end-point of any trajectory may be impossible to define, expected performance measures can be established which allow progress along the trajectory to be monitored and assessed. For example, a trajectory focussing on control of pest fish may have a performance target of reducing carp biomass by a given percentage in a proportion of monitoring sites within a defined time, allowing achievement of the target on a probabilistic basis rather than on an all-or-nothing assessment (Koehn, Brumley and Gehrke 2000). Once this target is achieved, a subsequent target may be to reduce carp biomass further at those same sites, or to extend the same level of reduction to a larger proportion of sites. This approach lends itself well to an adaptive management framework in which scientific assessment is an integral component of the target setting and performance evaluation process (Walters and Holling 1990, Walters 1997). Rebuilding therefore becomes an iterative process that can be adapted over time to take advantage of new information as it comes to light while at the same time retaining sensitivity to changing stakeholder perceptions, expectations and values.

Data requirements for rebuilding freshwater ecosystems

Freshwater fisheries in Australia focus heavily on the upper levels of trophic organisation. Top predators such as Murray cod (Maccullochella peelii), Australian bass (Macquaria novemaculeata), golden perch (Macquaria ambigua) and eels (e.g. Anguilla spp.) are the main target species in many areas. Other target species at lower trophic levels include carp (Cyprinus carpio) and yabbies (Cherax destructor). Yet fisheries conservation issues cover all trophic levels from nutrients and producer communities right through to top aquatic predators and in some cases to terrestrial predators. Each level of organisation consists of numerous species, each with its own population dynamics, interspecific actions, physical habitat associations, and hydrology and water quality interactions (Figure 1). These interactions ultimately dictate that the data required to rebuild populations of a single species include many layers of complexity, extending to species and trophic interactions, harvest rates for different species, and ecosystem processes. Complex data requirements have long been recognised as a challenge for effective management at the level of fish communities and aquatic ecosystems (Evans et al. 1987) and this situation is exacerbated in fisheries which tend to be low value, data-poor, and with limited scope to support expanded information gathering.

Figure 1. Diagrammatic representation of a riverine trophic pyramid, and the influence of some ecosystem processes on each interdependent trophic level. Arrows depict the influence of bottom-up (e.g. nutrients and prey availability) and top-down (e.g. predation, grazing) processes in interactions among trophic levels.

Many of the tools required for rebuilding fish resources are already available (Pitcher and Pauly 1998) and include information on population dynamics, ecosystem modelling, various fisheries management approaches (e.g. reserves, restrictions on gear, effort, and catches), knowledge of historical condition, and socio-economic cost:benefit assessments. Within freshwater systems additional tools for ecosystem restoration, such as enhanced environmental flow or reintroduction of woody habitat, are also available.

Whilst the basic tools exist, the availability of data to determine the sustainability of freshwater fisheries and to assess the performance of rebuilding programs remains a problem across Australia (Kearney 1997). Fisheries agencies surveyed in each State indicated that the recreational fishery sector is characterised by very poor data at a large scale, with most States awaiting the results of the Australian National Recreational Fishing Survey (Table 2). Specific components of the recreational sector have better data than the sector as a whole, examples being the extensive data generated by the Basscatch and Freshwater Angling Database projects run by NSW Fisheries. Monitoring programs such as the NSW Rivers Survey (Harris and Gehrke 1997) provide extensive data on species distributions and abundance, but even these large projects struggle to meet the data requirements of population or ecosystem modelling tools.

Table 2. Data availability for freshwater fishery sectors by State or Territory jurisdiction. Black cells: little or no data; dark grey cells: data adequate for some purposes; light grey cells: data adequate for sector management purposes. Empty cells indicate a non-existent sector in that jurisdiction. (informal survey of freshwater fishery scientists in each jurisdiction)

Sector	Qld	NSW	ACT	Vic	Tas	SA	WA	NT
Commercial
Recreational
Conservation

Not surprisingly, the best data is available from areas where fish are perceived to be under greatest threat, whereas from areas where threats are perceived to be low (such as the Northern Territory and large areas of Western Australia) there is limited data to assess current or potential threats. Therefore, when new threats are realised there is little historical data on which to base projected impacts.

Because of the paucity of biological data matched with economic value for harvested fisheries, the capacity to predict responses of fisheries to management intervention and environmental events is limited. The situation is worse for non-harvest species. Data on other trophic levels is patchy and is often held by agencies other than fisheries agencies. Accordingly, the limited amount of data available confers a high level of uncertainty over the likely outcomes of freshwater ecosystem management actions.

Solutions to data availability

The only solution to a lack of data is a data collection program. Where the species or life-history stages of interest are not collected by a fishery, an independent survey is required. But fishery-independent surveys are expensive to conduct, especially so where the spatial scale of interest is large; and the added cost of repeating the survey over time can be prohibitive. Programs such as the NSW Rivers Survey (Harris and Gehrke 1997) have developed efficiencies in the design of freshwater fish surveys in relation to the spatial and temporal intensity of sampling required and maximum gear efficiency, but cost remains a significant factor in data collection. In Australia, the cost of assessing freshwater fish resources is exacerbated by the lack of large-scale commercial fisheries that can fund the work. Instead, fishery-independent sources such as the water industry support many resource assessment activities. Even though data is being collected, the shortage of data remains as an impediment to sound fisheries and ecosystem management.

Walters (1998) observed that successful fisheries have large refuges in space and time not targeted by effort. Where effort is directed on only a small portion of the resource, the impact of the fishery is also small. In contrast, as advances in technology have allowed fisheries to expand, the refuges have diminished in size or duration, necessitating an increase in the level of management sophistication and concomitant data requirements to protect the stock from over exploitation.

Most freshwater fisheries in Australia have large refuges in space or time not targeted by fishing effort and are characterised by poor data availability. Yet the refuges are seriously impacted by other disturbances that directly affect the fish. Examples are the commercial freshwater fishery in New South Wales which, before its closure in 2001, had access to only 5% of the rivers in the State (Reid, Harris and Chapman 1997) compared to the large-scale impact of altered river flows (Gehrke and Harris 2001). Large-scale freshwater reserves, as proposed by Walters (1998), would certainly provide protection from over-exploitation without the need for accurate stock assessment data and models, but to be effective in allowing fish populations to recover, reserves also need to provide protection, or allow recovery, from other forms of catchment degradation. Despite the difficulty of establishing effective reserves that provide refuge from degradation, freshwater reserves containing undamaged or rehabilitated habitat are a fundamental component of the process of rebuilding Australia’s freshwater fish resources.

Future data needs

The data to develop and assess the success of restoring aquatic ecosystems need not replace fish stock assessments, but rather needs to include fish assessments. Such a broader framework could involve indicators of ecosystem condition linked to target trajectories through performance measures. Fish indicators could be derived from catch-effort data from recreational and commercial fisheries (where they exist) and independent surveys to fill data gaps at an appropriate level of resolution. An approach along these lines is currently being implemented for the Sustainable Rivers Audit by the Murray-Darling Basin Commission.

Outlook for sustainability

The outlook for true sustainability of freshwater fisheries – that is, rebuilt aquatic ecosystems that support fish populations that can be harvested without risk – is uncertain. The concept of restoring or rebuilding an ecosystem involves the implicit assumption that processes of decline are reversible, and that a system will revert to its previous condition once the threatening processes are removed. This assumption has not been validated at a general level and remains a matter of conjecture.

The success of target trajectories in rebuilding is likely to be dependent on the level of commitment to adaptive management to evaluate achievement of performance targets, and to establish new targets. Philosophical differences in approach between scientists and managers make it difficult to maintain an effective adaptive management program unless all parties are fully committed to the intended outcomes (Walters 1997).

Another source of uncertainty lies in the ability of existing environmental management programs. Despite the intentions of a historical legacy of programs to halt environmental degradation, degrading processes continue throughout Australia. If we cannot halt degradation on a large scale, is it realistic to consider that we have the ability to rebuild functional aquatic ecosystems?

References

Evans, D.O., Henderson, B.A., Bax, N.J., Marshall, T.R., Oglesby, R.T. and Christie, W.J. 1987. Concepts and methods of community ecology applied to freshwater fisheries management. Canadian Journal of Fisheries and Aquatic Sciences 44 (Supplement 2): 448-470.

Gehrke, P.C. and Harris, J.H. 2001. Regional-scale effects of flow regulation on lowland riverine fish communities in New South Wales, Australia. Regulated Rivers: Research and Management 17: 369-391.

Harris, J.H. and Gehrke, P.C. 1997. Fish and rivers in stress – The NSW rivers survey. NSW Fisheries Office of Conservation, Cronulla, and the Cooperative Research Centre for Freshwater Ecology, Canberra. 298 pp.

Kearney, R.E. 1997. Issues affecting the sustainability of Australia’s freshwater fisheries resources and identification of research strategies. FRDC Research Report 1997/142.

Koehn, J., Brumley, A. and Gehrke, P.C. 2000. Managing the impacts of carp. Bureau of Resource Sciences, Canberra. 247 pp.

Pitcher, A.J. and Pauly, D. 1998. Rebuilding ecosystems, not sustainability, as the proper goal of fishery management. pp 311-329, in T.J. Pitcher, P.J.B. Hart and D. Pauly (eds), Reinventing fisheries management. Kluwer Academic Publishers, Dordrecht.

Reid, D.D., Harris, J.H. and Chapman, D.J. 1997. NSW inland commercial fishery data analysis. NSW Fisheries and Cooperative Research Centre for Freshwater Ecology, Cronulla. FRDC Project No. 94/027. 44 pp plus appendices.

Walters, C.J. 1997. Challenges in adaptive management of riparian and coastal ecosystems. Conservation Ecology [online]1(2):1. Available from the Internet. URL: http://www.consecol.org/vol1/iss2/art1

Walters, C.J. 1998. Designing fisheries management systems that do not depend upon accurate stock assessment. pp 279-288, in T.J. Pitcher, P.J.B. Hart and D. Pauly (eds), Reinventing fisheries management. Kluwer Academic Publishers, Dordrecht.

Walters, C.J. and Holling, C.S. 1990. Large-scale management experiments and learning by doing. Ecology 71: 2060–2068.

Welcomme, R.L. 2001. Inland fisheries: ecology and management. Fishing News Books, Oxford. 358 pp.