Fecundity studies on the New Zealand quinnat salmon in the Rakaia River, Canterbury in relation to fish-stock management

Abstract

The Rakaia River salmon population supports a sports fishery which is widely utilised by local fishermen. An increase in the angling pressure on the salmon run, proposals to use South Island Rivers for irrigation and hydro-electric development, their use for effluent disposal and the possibility of a commercial enterprise enhancing and harvesting salmon stocks, has led to a concern for the continued viability of the salmon fishery in the Rakaia River. If the fishery is to remain viable under these pressures, the salmon stocks must be properly managed.

The Fisheries Research Division of the Ministry of Agriculture and Fisheries is conducting long-term studies into the biological and ecological aspects of the salmon population in the Rakaia River. The overall objective of the research programme is "To preserve, and if possible enhance, the numbers and quality of quinnat salmon in South Island waters."

This study concerns the execution of Project 5.1 (Part 1): The estimation of egg depositions, with the objective of obtaining estimates of the numbers of eggs deposited in the Rakaia River system during the 1975-1976 salmon run. A further objective of this study was the application of these results to formulate management objectives for the juvenile salmon population.

A representative subsample of the Rakaia River salmon run was taken by angling. Fecundity, age, length and scale nucleus type were recorded for each fish. The average fecundity was 4,876 eggs.

The relationship between fecundity and length was determined by regression analysis. The regression equation obtained was: logY = -0.21 + 2.08 logX where Y = fecundity and X = length.

The total egg depositions for the entire Glenariffe run, and the juvenile egg-to-outmigrant survival rate were estimated. This information provided the basis for recommendations for the management of quinnat salmon in the Rakaia River.

It was recommended that enhancement of the salmon run could be achieved by increasing the fry outmigrant survival rate by retaining fry in holding ponds. A consequent increase in the adult salmon population would need to be accompanied by an increase in suitable spawning areas or a change in the regulations governing catch limits, and an increase in the number of fry retention ponds.