Chinook Salmon Fisheries Research - Evaluating performance at Lakes Bullen Merri and Purrumbete

Executive summary

The volcanic crater lakes of southern western Victoria, Lakes Purrumbete and Lake Bullen Merri have long supported high quality and productive recreational salmonid fisheries. Both lakes are regularly stocked with hatchery-bred rainbow trout, brown trout and chinook salmon to sustain popular and productive put-grow-and-take recreational fisheries.
The study aimed to use available angler information (local angling club data catch records and creel surveys of public anglers) and fishery independent data to quantify the performance of brown trout, Chinook salmon and rainbow trout in Lake Purrumbete and Lake Bullen Merri during the trial stocking period between 2012 and 2016 and, compare this to previous years.
Angler catch data were obtained from angling club records (2012-2016), a creel survey of Lake Purrumbete conducted during the present study (2013-2014), historical creel surveys (1962-2003) and social media. Fishery independent data were obtained from netting surveys conducted between 1978 and 2009.
Angling club records provided valuable information on 2,367 caught fish (including 708 salmonids), which contributed to the assessment of fishery performance. During the 2013-14 creel survey of Lake Purrumbete, 1,112 anglers were interviewed and 2,367 fish (including 707 salmonids) were recorded. Most anglers (86%) targeted salmonids. Social media postings highlighted large (trophy) fish, being caught from Lake Purrumbete and Lake Bullen Merri in recent years. Other specific findings included:

Chinook salmon

The reintroduction of Chinook salmon into Lake Purrumbete and Lake Bullen Merri has been well received by most anglers and celebrated as highly successful as indicated by the presence of increasingly larger fish in angling club records from 2012-2015 and social media.
Social media reports from March 2016 onwards highlighted trophy Chinook salmon (4-8kg) catches by anglers.
The 2013/14 creel survey of Lake Purrumbete indicated that the catch rate for Chinook salmon was 0.1 fish/ angler hour, which was the same as the long term mean or average (LTM) value.
In the angling club records for Lake Purrumbete, average annual values of length, weight and condition factor (K ) values have increased between 2012 to 2015, but were below LTM values.
In the angling club records for Lake Bullen Merri, average annual values of length and weight records have increased between 2012 to 2015, whereas K values have declined.
Brown trout stocking in Lake Purrumbete appears to have had a negative effect on the Chinook salmon fishery as the angler catch rate, and length and weight of Chinook salmon have declined with increasing numbers of brown trout stocked in previous years.
The K factor of Chinook salmon angled in Lake Bullen Merri increased with increasing numbers of rainbow trout stocked, possibly suggesting that the newly stocked rainbow trout may be prey for larger Chinook salmon.
Based on the performance of Chinook salmon in the creel survey, angling club records and social media reports, it is recommended that stocking of Chinook salmon into both crater lakes be maintained.

Brown trout

The catch rate of brown trout in the recent Lake Purrumbete creel survey (0.01 fish/angler hr) was lower than the LTM of 0.03 fish/angler hr, however, average annual lengths and weights of brown trout recorded in angling club records were higher than the LTM value.
Social media reports highlighted trophy brown trout (4.5kg+) catches by anglers during the study period, in particular at Lake Purrumbete from May 2016 onwards.
In Lake Bullen Merri, average annual length, weight and K factor estimated from angling club records increased from to 2012 to 2014, but declined in 2015, which may have reflected changes in stocking activities.
Angler catch rates of brown trout in Lake Purrumbete increased with increasing numbers of brown trout stocked in the previous two to four years, but declined with increasing numbers of rainbow trout stocked in the previous two to three years.

Rainbow trout

The catch rate of rainbow trout estimated from the recent creel survey of Lake Purrumbete was 0.005 fish/ angler hr, which was considerably lower than the LTM of 0.05 fish/angler hr.
Social media reports highlighted well-conditioned rainbow trout (2kg+) were caught by anglers from March 2016 onwards.
Mean annual length, weight and K values of rainbow trout recorded in angling club records for Lake Purrumbete have generally declined since 2012.
Mean annual length and weight values for Lake Bullen Merri were generally consistent with LTM, but K values were variable and, apart from 2014, were generally lower than LTM.

Redfin

Redfin were the most abundant species at Lake Purrumbete as evidenced by the creel survey and angling club catch records.

It should be noted that the long term mean or average (LTM) comparison of catch rates takes into account a variety of fisheries management regimes, water levels and climatic periods, therefore its relevance needs to be carefully considered with respect to recent fishery performance. The information presented in this study was shared with fishers at a public consultation forum at Lake Purrumbete Angling Clubrooms on 12 March 2015 and as a result revised stocking plans for 2015 and 2016 for the Crater Lakes were agreed (Appendix II). This evaluation of the performance of the stocked fisheries of Lakes Bullen Merri and Purrumbete has improved the understanding of the effects of fish stocking strategies, and informed management decisions to improve outcomes for recreational fishers. In partnership with the Lake Purrumbete and Camperdown Angling Clubs and local anglers, further work is currently underway to better understand and further improve the Crater lakes fisheries including a rainbow trout strain stocking trial, brook trout stocking trial and modelling of redfin populations. In consultation with key stakeholder groups, such as through the annual rounds of the Vic Fish stock regional consultative meetings, these studies will help inform future decisions regarding the management (and stocking) of these popular and productive recreational fisheries.

Further information

For a copy of the full report please email richard.rogala@vfa.vic.gov.au