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Diet, vertical distribution and movements of brown bullhead catfish (Ameiurus nebulosus) in southern Lake Taupo, New Zealand

Michel Dedual

Department of Conservation, Private Bag, Turanga Place, Turangi, New Zealand

Brown bullhead have been reported present in Lake Taupo since 1985. It is unclear how they arrived in the lake. Previous studies indicated that catfish in shallow, weedy, or rocky habitats did not include trout in their diet and that crayfish were a rare item found in their stomach.

The catch per unit effort (CPUE) of catfish monitored monthly since 1996 doesn’t point to any increase in population. The monitoring results show that during summer 1997-98, catfish vacated the shallow weedy and rocky habitat. Subsequent underwater observations revealed large numbers of catfish (shoals up to 1000 fish) in mid-water along the drop-off of the lake and close to the river mouths. Catfish caught in these habitats were larger than in shallow water and their diet included more smelt, bullies, and freshwater crayfish (koura) but no trout were found in the stomachs of catfish.

Ultrasonic telemetry revealed that catfish swam in water from 0 to 17 m deep but showed some seasonal preferences. Catfish were more active at night when they used shallow water extensively. The fish also made short dives and ascents, especially at dusk as they moved from deep to shallow water. Brown bullhead were the most mobile in spring when they left Motuoapa Bay, suggesting migratory behaviour. During winter the fish remained more stationary, moving around inside the bay only. The results of this study provide guidance for establishing a catfish control program should it become necessary.

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