Carp in Lake Sorell
For many southern anglers Lake Sorell has been one of the most popular, accessible and productive brown trout fisheries. Its shores were home to private shacks, club shacks, and hundreds of campers.
That is until the sudden infestation of carp, a problem that continues to plague this water. Despite continuing efforts since 1995 by the Inland Fisheries Service to eradicate the pest, the Spring of 2009 saw an increase in juvenile carp which, according to IFS Director, John Diggle, was “the biggest spawning event we have had.”
It is estimated that around 5,000 carp are now swimming around Lake Sorell where as prior to last year’s spawning, numbers were less than 50.
According to the Director, “The good thing is that these fish are all juveniles and as they are unable to breed for a couple of years we have a window of opportunity to wipe them out.”
IFS staff have already taken out over 14,000 carp from Lake Sorell last summer, and it is vital to eradicate mature carp as soon as possible as a four kilogram carp has the potential to lay one million eggs.
John Diggle believes Lake Crescent is now free of carp and that, in itself, is quite an achievement. No juveniles have been found since 2000, and no adult females have been detected for nearly three years. According to Diggle, “It is a clear demonstration that we can and will eradicate carp from Lake Sorell.”
Although carp do eat some macro-invertebrate species that brown trout also enjoy, they are not predators of trout fry or fingerlings. The issue is what carp can do to the food chain and to the water quality.
Compounding the presence of carp in Lake Sorell is the issue of poor water quality resulting from drought conditions. This is also impacting on Lake Crescent. Both waters have high levels of turbidity – colloidal particles in suspension which don’t settle to the bottom of the lake bed. According to Diggle, “It’s a bit like a farm dam that doesn’t clear, and that just isn’t attractive to anglers.”
Whilst this is a result of drought conditions in this part of the island, low water levels back in 2000 also contributed, especially in Lake Sorell where there has been some erosion of the lake bed.
Currently the water management plan for the Clyde catchment area is under review, and there will obviously be some discussion around critical minimum water levels necessary to sustain both trout fisheries, and especially for the protection of Golden Galaxias in Lake Crescent. No doubt other stakeholders – irrigators and local town water supplies – will be seeking their share of the resource. But there is no doubt that the IFS is putting a strong case for critical minimum water levels so that this fishery can once again be a prime destination for trout anglers.
If water levels can be sustained, the carp eradicated, and water turbidity controlled there is no reason why Lake Sorell can’t regain its former status as one of the state’s top fisheries which used to attract 50% of the state’s anglers in any one season. Afterall, there is a very good head of fish in Sorell resulting from excellent natural spawning conditions, albeit dependent upon variable rainfall patterns.
According to the IFS Director, “That’s what I want … that’s what I have been working on for years. However, our problem may not be so much about carp or water quality but climate change. If the things people are saying about climate change are true, and it is only going to get drier than we are now, the future may not so promising for either lake, or for most of the eastern part of the island.”
Then again, Lake Dulverton is now full and has been stocked; Tooms Lake is spilling and has also been stocked; and Craigbourne Dam should again deliver angling delights for southern family expeditions to this water.
So it looks like at least two years before Lake Sorell will again be open for anglers, although the IFS will assess the situation at the end of each summer.