Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7
Aquatic ecosystems (continued)
Responses to improving and protecting aquatic ecosystem issues have been of many types and have included federal, state and local government policies, legislation, administrative structures, community education, direct management, setting of resource-use targets, as well as initiatives taken directly by communities themselves. These responses can be strategic or can be applied at a local level. In many cases it is not yet possible to gauge the success of these responses due to lack of data or the early stage of progress. The extent of implementation of responses is assessed in Table 42. Responses to many problems or issues have not yet been developed and these are also discussed.
The physical barriers to fish migration from dams and weirs can be overcome in some cases with the construction of fishways or 'fish ladders'. Most dams and weirs in Australia do not have fishways and many existing fishways are ineffective. For example, 22 fishways in Queensland rivers are ineffective, as they are either too steep, the water flow is too turbulent or they do not work during extended periods of low flow (Queensland EPA 1999). Alternative types of fishways are being trialled on instream barriers in Queensland. One option being trialled is a vertical-slot fishway.
A vertical-slot fishway on the Fitzroy barrage at Rockhampton has been extremely successful passing over 500 000 fish annually from 20 mm gudgeons to 1300 mm adult eels (DPI 2001). More significantly up to 100 juvenile barramundi have migrated daily to traditional freshwater habitats, the first fishway to effectively pass barramundi in Australia (DPI 2001).
The results of these trials, and similar ones being undertaken by other states and territories, will have significant benefits for native fish populations. All state fisheries organisations and federal fisheries programs need to allocate significant resources specifically for work on fishway design as better knowledge remains an urgent priority, particularly in the areas of migratory fish behaviour, and fishway hydraulics and design (Thorncraft & Harris 2000).
The Murray-Darling Basin Ministerial Council has recently agreed to spend $10 million on providing fish passage from the mouth of the Murray River to Albury (WWF 2001).
Fishways are only one mechanism used to protect and enhance native fish populations. Without appropriate environmental flows, good water quality and healthy instream habitat, the environmental benefits of installing a fishway will be limited (McGuckin & Bennett 1999).
Some states (e.g. NSW) are considering demolishing redundant weirs and other barriers to fish movements. Because of the significant potential impacts associated with this (i.e. the release of stored silt behind dams and weirs), a full environmental assessment of the removal is required.
Native and introduced freshwater fish bred in hatcheries are reintroduced to many Australian inland waters every year. The principal reasons for fish stocking are:
- recreational - maintaining the number and variety of the fish for recreational anglers
- environmental - restocking of fish species in order to conserve fish species or to control pests.
Restocking has often been a core component of conservation programs aiming to protect and/or restore the distribution of threatened species listed under state and federal legislation.
The stocking of inland waters with fish for pest control or the biomanipulation of reservoirs (Chudleigh & Simpson 2000) and has been trialled in Australia. The science of stocking for these purposes is in its infancy, forming an insignificant component of current stocking activities, although its importance may grow in future years if it proves to be successful.
The Queensland Government's fish stocking policy aims to encourage community and industry involvement and awareness and includes a decision-making protocol for assessing proposals for fish stocking. Regular restocking of barramundi (Lates calcarifer) and golden perch (Macquaria ambigua) is generally common and is undertaken by the local community for recreational uses.
Several restocking projects for conservation purposes have been undertaken. The Mary River cod is a protected species under the Queensland Fisheries Act 1994. The species was widely distributed but is now only found in parts of the Mary River system. A number of community-based hatcheries specialise in the production of Mary River cod and a program of stocking and monitoring is being undertaken in the Mary River.
Environment ACT stocks approximately 50 000 fish each year into Canberra's lakes, with more than 1.6 million fish stocked since 1981. Early stocking projects focused on introduced trout species, but the program has undergone a shift in emphasis towards native species such as Murray cod and golden perch. Over the last ten years the trout cod has been stocked into the Bendora Reservoir and the Murrumbidgee River in order to restore populations and meet objectives of the species Action Plan and the National Recovery Plan.
In Victoria, native fish are restocked to enhance wild populations or establish new populations. Trout are also restocked for recreational angling in some inland waters. As in the Australian Capital Territory, stocking of trout cod is part of the national focus for conservation of this species. During 1996/97, trout cod were released into the Nagambie and Ovens rivers. Other native fish releases include Australian bass, golden perch, Murray cod, Macquarie perch and silver perch. Releases during 1996/97 totalled 670 651 fish in 53 waterways and lakes throughout the state, while during 1999/2000, over 700 000 native fish were released.
The restocking of inland waters must be managed carefully. Undesirable outcomes of stocking include introducing disease into wild stocks, competition between hatchery and wild individuals and the risk of creating new pest populations. Loss of genetic diversity is seen as a major risk, reducing the ability of populations to survive environmental change, disease and other factors (Moore 2000). Stocking into natural populations can also make it difficult to evaluate whether conservation programs are achieving their objectives (Gehrke 2000).
The fact that fish species have declined in certain waterways is an indication that environmental conditions are no longer suitable for these species. Fisheries managers are increasingly recognising that stocking fish is not always the best response to fishery problems and that the maintenance of appropriate environmental conditions is just as critical for the purpose of stock enhancement or conservation. When stocking does occur, monitoring is a critical element in gauging the success and value of such stocking programs.
As part of the Action Plan for Australian Birds, 18 Coordinated Conservation Plans have been developed for birds. These have been based on conservation areas that contain at least five threatened and/or 10 near threatened bird species. Eight of the 18 conservation plans include birds known to associate with inland waters. The eight conservation plans were for the following biogeographical regions:
- subtropical forests (red goshawk)
- subtropical woodlands (Australasian bittern, painted snipe (Australian), little bittern (Australasian), grey falcon)
- temperate woodlands (magpie goose, black bittern, Australasian bittern, painted snipe, little bittern, grey falcon)
- eastern Tasmania (Australasian bittern, hooded plover)
- King Island (Australasian bittern)
- Mount Lofty (Australasian bittern)
- Two Peoples Bay (Australasian bittern)
- western region (western wheatbelt hooded plover).
The effect of modified flow regimes and volumes on inland aquatic ecosystems has been discussed previously. The progress of states and territories in establishing environmental water allocation is discussed in Environmental flow allocations. Although there has been some progress in the allocation of environmental flows, only 13% of regulated river systems had operational environmental flow allocations in June 2000 (NLWRA 2001b). However, most states and territories are in the process of developing environmental water allocations for all their regulated river systems.
The determination of environmental water allocations is a developing science, and research is focused on reversing human modifications to flow regimes and returning flows to as close as possible to natural conditions. This will enhance the health of aquatic species and habitats. In many river systems, it is too early to assess the effects of restored environmental flows.
For groundwater-dependent ecosystems the objective of environmental water provisions is to sustain key ecological values, while recognising economic, social and ecological goals. Groundwater allocations are currently determined with little recognition of groundwater-dependent ecosystems. One state has been describing specific criteria for groundwater-dependent ecosystems for many years, while other states have recently assessed environmental water provisions by allocating a fixed percentage of annual recharge to groundwater-dependent ecosystems.
This system of groundwater allocations generally places social and economic values over environmental values. With some groundwater management units recently identified as being over-used, this means since there has been little consideration of groundwater requirements of groundwater-dependent ecosystems, and many groundwater-dependent ecosystems may currently be affected by over-extraction of groundwater. Furthermore, when environmental water provisions for groundwater-dependent ecosystems are determined in the future, it is likely that many of the sustainable yield estimates will need to be reduced. This will obviously place significant stress on groundwater users.
It will require stakeholder participation to balance the economic, social and environmental objectives for the groundwater resource. A system will also need to be put in place to ensure that the process is monitored, reviewed and adapted to changing needs of the community and as a result of the actual impact on groundwater-dependent ecosystems.