We are lucky in Tasmania to have many self-sustaining trout fisheries, waters that provide good recruitment of trout stocks each year.
Successful natural recruitment requires adequate and reliable inflowing water between May and November each year. Ideally there should be minimal predation on the fry as they develop in the stream then drop into the main water body.
There are quite a few well known fisheries that fit these criteria such as Woods Lake, Arthurs Lake and Little Pine Lagoon but there are also quite a few that do not. It is the fisheries that cannot self sustain that the Service focuses the majority of its stocking efforts.
In the past, the Inland Fisheries Commission (the forerunner to the Inland Fisheries Service) provided fishing opportunities in as many places as possible. This meant stocking farm dams, coastal lagoons such in the northeast and many other smaller water bodies that do not have inflowing water. Quite a few of these opportunities have been maintained over the years and there are many examples; Big Lagoon (Bruny Island), Blackmans Lagoon, lakes Duncan and Lynch, Beaconsfield dams, Carters Lake and Lake Botsford to name a few of them.
Some of the waters that were once stocked by the Commission are no longer stocked due to changes in conditions or changing priorities for the IFS, such as Calverts Lagoon in the South and some of the lakes around Strahan in the West. Several of these ‘put and take’ waters are maintained with adult transfers of brown trout where fish are taken from the spawning runs, usually Great Lake. A number are stocked on an annual basis with fry and others are topped up when the opportunity arises from surplus of domestic stock provided by commercial fish farms.
Larger more popular fisheries demand most of the stocking effort. Many of the impoundments created for hydro-electric generation in the period from 1950s to 1970s have provided reliable places for people to fish for trout. Whilst these lakes have self sustaining populations, there has been an increasing need to stock these fisheries in order for them to perform to a standard that keeps anglers happy.
Arthurs and Great lakes are two differing examples of hydro storages. The former has never required restocking after trout were initially established, while the latter requires restock in order to balance the two species of trout available there.
Great Lake has been the focus of stocking aimed at increasing the rainbow trout population over the last 30-40 years. The current strategy involves stocking moderate numbers of hatchery-reared fingerlings from wild stock. Their parents were harvested from the wild so no selective breeding has taken place. This defines ‘wild’ stock, whereas domestic stock is produced through generations of selective breeding.
Hydro generation impoundments including some of the most popular fisheries, also exhibit one factor that necessitates stocking, the presence of pest fish, specifically redfin or English perch. Populations of redfin perch have flourished at a number of waters over the last 20-30 years. Key examples are Craigbourne Dam, Brushy Lagoon, lakes in the Derwent system from Wayatinah Lagoon downstream, the Bradys chain of lakes, Lake Echo, Dee Lagoon and Lake Leake.
While it may be that some recruitment takes place with a few fry escaping the eager mouths of redfin as they drop into the lakes, the case is that recruitment is hampered by populations of these fish. Whilst eradication of perch has been attempted it is not the practical solution nor has it proved to be successful in anything larger than small ponds. The better solution is to supplement the waters that have redfin populations with larger fish.
In recent years (since 2007), the Service has been able to produce larger juvenile fish at a quicker rate due to the construction of a recirculating hatchery at the New Norfolk base. The use of fish greater than 20g has meant greater survival of trout stocked into redfin populated waters and also reduced predation by trout themselves which is of particular importance when trying to re-establish rainbow trout stocks at Great Lake.
- Tim Farrell - Senior Fisheries BiologistReads: 4326