Carp Activity - Warming Up for Summer

The total number of carp captured since the carp program began in 1995 is 2,798 from Lake Sorell and 7,797 from Lake Crescent. Apart from the general fish down of carp in both lakes, a key method to eradicate carp has been the use of male carp to monitor population behaviour through radio tracking. Male fish are surgically implanted with a battery powered radio transmitter, with a two year battery life, and the fish are released back into the lake for the Inland Fisheries Service to monitor through regular radio tracking.

This regular surveillance enables staff to keep a watch for spawning activity since carp aggregate prior to a spawning event. When several males are tracked in the same vicinity, a spawning aggregation is likely to occur, enabling the Service to focus its fishing effort in that area for greater effectiveness and hopefully to capture female fish. Spawning generally occurs during the warmer months, so radio tracking surveillance becomes increasingly intensive during Spring and Summer months.

As expected, the wet season and high lake levels have provided ideal conditions for the carp to begin their spawning activity. The male carp that were fitted with transmitters during Winter have been very active over the past six weeks requiring intensive monitoring by the Service. The carp program entered its daily monitoring phase at both lakes from the start of October and intensive fishing has been ongoing during this period.

In Lake Sorell, barrier nets have so far prevented carp access to their ideal spawning habitat in the large marshes at Robertson’s and Kermodes. Fishing has been concentrated in the marshes at Silver Plains, which is the only remaining accessible marsh area. Four spawning aggregations were removed from this area and a total of 34 carp were caught during Spring. Passive fish traps accounted for 17 of these fish (including three expired transmitter fish) at a variety of sites around the lake.

Lake Crescent has presented an interesting series of events over recent weeks. As the lake level rose through the front of the marshes, the transmitter fish were captured repeatedly including two with transmitters that had expired. The lake continued to rise until it reached a point where the carp could easily bypass the traps and had open access to the back marshes. Over a number of days the transmitter fish began to aggregate at the top of the lake near the Interlaken Road and could easily be observed swimming in the shallow clear water.

Initially three of the six transmitter fish grouped together but careful observation using polaroid sunglasses and transmitter signals indicated that there were no other fish with them. Many large eels were seen. A fourth tracker fish joined the aggregation after two days followed by a fifth on the next day. The carp team then targeted the aggregation with gill nets and back pack electro-fishers capturing all the transmitter fish along with a further two transmitter fish that had run out of battery.

The event was significant in that despite the fish aggregating in shallow water and being extremely active in full spawning mode, no females were captured. This level of activity has not been observed before without the presence of female fish. The male transmitter fish have been targeted on 15 occasions over the past month, and although the existing transmitter fish have been captured repeatedly no female carp have been caught. This result indicates that the presence of any female carp remaining in the Lake Crescent  is very low, indicating the success of the eradication strategies.