- Fish stocking should only be undertaken if the need has been clearly established and there are no alternatives.
- Genetic management is vital if wild genetic diversity is to be maintained to ensure the wild population maintains the ability to adapt to environmental change, disease and competition.
- Fingerlings must be only obtained from hatcheries where there is a quality assurance program. Stocking should only be undertaken when a five year program has been developed and funds are guaranteed over this period.
- All hatchery released fish should be marked (e.g. tagged in some way so they can be distinguished from wild fish) so that the contribution of stocked fish to the population can be monitored.
Stocking hatchery reared fingerlings of native fish species (particularly recreational species like Murray cod and Golden perch) is widely practiced in most parts of Australia, and all jurisdictions in the Basin apart from South Australia. It is a commonly used fisheries management tool, and has created recreational fisheries in artificial impoundments as well as temporarily boosting fish numbers in riverine situations. There are however potential negative impacts from fish stocking. These include:
- Impacts on wild population genetics from interbreeding with genetically inferior hatchery reared fish.
- Introduction of disease.
- Translocation of non-target species (including non-desirable fish species and invertebrates).
- Masking of underlying causes for wild stock depletion.
- In demonstration reaches, masking the impacts of habitat rehabilitation activities on fish populations (e.g. are population increases due to stocking or habitat rehabilitation?).
Stocking is a short term fix that should only be used as a last resort, for example, where there is a spawning bottleneck that cannot be resolved by habitat rehabilitation. It may also be appropriate where an endangered species is being re-introduced to its native habitat.
Is there a need to stock?
The key questions is whether there is compelling evidence that wild populations are severely depleted and that other actions e.g. habitat rehabilitation, changes in fishing regulations etc., cannot be used to rehabilitate wild populations? Is there an identified bottleneck (e.g. lack of recruitment) that cannot be overcome any other way? Is it an endangered species that is being re-introduced to its native range?
If the answer to any of these questions is yes, then stocking could be considered as a management tool. It needs to be undertaken with the goal of rehabilitating wild populations, not to enhance recreational fisheries. In the long-term, together with habitat rehabilitation, it may well lead to enhanced recreational fisheries.
Do we understand the genetic profile of the wild stock?
It is important to know the genetic variability inherent in the wild population to assess whether suitable fingerlings can be produced in a hatchery. Without this information it is best to harvest broodstock from the river you are seeking to stock and use these fish in hatchery production of the fingerlings.
Working with a hatchery where there is sufficient quality assurance to reduce the risks of disease transfer and translocation of non-target species etc. to an acceptable risk level (e.g. some NSW hatcheries are part of a Hatchery Quality Assurance Program) is also a good idea.
Developing a stocking management plan:
Stocking needs to be undertaken over a five year period, with sufficient numbers released to ensure the establishment of a diverse population structure. It is important to investigate whether the hatchery able to produce fingerlings over this time frame, as well as whether you have the funds to maintain the stocking program over five years.
Release of the fingerlings:
All fingerlings should be marked before release so that their contribution to future sampling is known (see Example 4k).
Stocking with Macquarie Perch- Hollands Creek Demonstration Reach, Victoria
Macquarie perch is an endangered species, listed both nationally and at the state level in Victoria. It occurs naturally in Hollands Creek, but recently only in small numbers. Electrofishing surveys of the demonstration reach in 2008/09 recorded only five Macquarie perch from a single pool. There were no Macquarie perch smaller than 270mm in length. Reasons for the lack of small individuals were unclear, but continued inability to recruit smaller individuals would undoubtedly have a negative impact on the long-term survival of the Macquarie perch population in the demonstration reach. A recommendation was made that Macquarie perch be stocked into Hollands Creek.
In 2010/11 sampling the numbers of Macquarie perch were still small but had doubled since 2008/09 and were similar to the number recorded in 2007/08. In February 2010, 300 Macquarie perch fingerlings were stocked into Hollands Creek. They were sourced from Snob’s Creek Centre
Surveys in 2012 recorded the highest number of Macquarie perch since the project began and the geographic distribution increased from two to four sites. Flooding has changed the creek habitat improving connectivity between the bottom four sites enabling Macquarie perch to access habitat that has been unavailable to them over the last five years.