Lake Sorell Carp Eradication Update
High rainfall in October resulted in Lake Sorell rising quickly. By the start of November, Lake Sorell was 150mm over the full supply level. The last time the lake had filled to this level was in October 2016, when there was still a quite large population of carp, and many were caught in traps set in barrier nets in front of the marshes. With the lake level and temperature also rising at a similar time this year it provided a good chance to test the theory that few carp were left, and to catch any remaining carp in the lake. The strong spawning cues were likely to draw carp into the shallows, making them easier to catch. However, it also meant that we had to be on high alert, given the risk of spawning in the marshes was possible.
The fishing strategy for the 2021/22 carp season was to focus on spawning related carp movement and blocking spawning. This has included blocking the marshes with barrier nets, trapping the preferred carp entrance points to these areas, and targeted gill netting combined with electrofishing.
Fishing started in late October, and a total of four carp have been caught up until the end of December. One carp was caught in a trammel net set while using the electrofishing boat, another was caught in a trammel net set behind the barrier net in the marshes, while two carp were caught in barrier traps. The carp ranged in size from 800 to 2344 grams, and all four were females. Of the four females, three of the fish had gonad tumours and could not spawn. The other female carp appeared to healthy, carrying 334gm of eggs, with a gonadosomatic index (GSI) of 20% which is quite high. However, all the eggs were completely intact, indicating she had not spawned. The last healthy, sexually mature male carp was caught on 16 December 2018. It is increasingly likely that any remaining carp in Lake Sorell are unable to breed.
41 503 carp have now been removed from Lake Sorell since their discovery in 1995. There has been no sign of spawning so far from juvenile carp surveys this season. Surveys will continue each month through until March. These surveys involve electrofishing with the boat and backpack, fine mesh dip netting, fine mesh fyke netting, and visual checks in spawning habitat. Targeted fishing will continue into January if good weather conditions arise.