Otamangakau fishing survey for trophy trout

Waimarino Bulletin, Volume 6, Issue 257, 4 October 1988, Page 5

Otamangakau fishing survey for trophy trout

A small group of anglers keenly anticipated October 1 and the opening of the fishing season on Lake Otamangakau.

In the past few seasons this lake, while not having high catch rates, has yielded a number of exceptional trophy fish. Those anglers who have persevered and learnt the secrets of fishing the lake have been rewarded with regular catches of rainbow trout of 4.5 kg and larger. This year anglers fishing Lake Otamangakau or the nearby Whakapapa river may discover a tagged fish has taken their lure. Such fish are part of a research project being carried out by the Department of Conservation. Six hundred Taupo strain rainbow trout fingerlings and 6 0 0 rainbow fingerlings from parents captured in the Ruakituri River were released into the upper Whakapapa river in late 1987. Fish in the Ruakituri river re-

main in the river for their whole life unlike Taupo fish which migrate to the lake as juveniles, returning to the rivers „only as mature adults. This behaviour in the Whakapapa River causes young rainbow trout migrating downstream to follow the flow and pass through the Tongariro Power Scheme diversion tunnel into Lake Otamangakau. The problem occurs when after two years they are ready to spawn but are unable to swim back up the diversion and are lost from the river system. The aim of this study is to determine whether progeny from the Ruakituri stock retain the tendency to be river resident and stay in the Whakapapa system, or if they adopt a similar behaviour to Taupo strain fish and appear

in Lake Otamangakau. A characteristic o f Ruakituri fish is that they often a 1 1 a i n weights in excess of 4.5 kg. A further 600 fish of each strain were liberated into Lake Otamangakau and com-

parison of data returns for the two strains over the next three or four years should indicate whether in fact the large size of Ruakituri fish is likely due to the presence of 'large' genes or the occurrence

of optimum environmental conditions for growth in the Ruakituri River. The information which may be gained from this study could be significant to the future management of river resident fisheries. In New Zealand there are numerous rivers which are suitable for trout, many of which supported good trout fisheries in the past. However, because of hydro developments, water abstractions and diversions, barriers exist on these rivers which prevent trout migration between juvenile and adult habitats. This problem can be overcome if a strain of rainbow trout which do not migrate within the river during the course of their life can be obtained for liberation. One outcome of this study will be to determine whether the Ruakituri could provide this strain of river resident fish. If large size is due to genetic structure, such genetics could b e selectively bred to increase the trophy potential of certain waters.

To get valxd results the Department of conservation is dependant on anglers returning information for all tagged fish they capture. Information required includes the date of capture, tag colour, shape, letter and number, the length of the fish and the p 1 a c e where the fish w a s caught. Forms on which to

fill in data will be available from stores in the Waimarino, Turangi and T aupo areas or data may be passed directly to the department 's local offices. Information on access to and methods of fishing Lake Otamangakau or the Whakapapa River is available from local sports stores or from the Department of Conservation.