Long-term trends in the catch characteristics ofrainbow trout Oncorhynchus mykiss, in a self-sustained recreational fishery, Tongariro River,New Zealand

The catch distribution of adfluvial rainbow trout, Oncorhynchus mykiss (Walbaum), amongst anglers is described from 14868 creel surveys collected from the Tongariro River in central North Island of New Zealand between 1985 and 2013. An index of fish abundance was obtained during the period 1998-2013 from a continuous trapping programme on the Waipa Stream, an important spawning tributary of the Tongariro River. Using these two data sets, inequalities in catch distribution were quantified using the Gini coefficient and Lorenz asymmetry coefficient (LAC). Both Gini coefficient and LAC showed a slight decline over time. This occurred concurrently with reduced angling participation and a decline in fish abundance. Inequality was larger when fish were more abundant, but catch-per-unit-effort was only marginally affected despite large variations in fish abundance, suggesting that some hyperstability is occurring. Several important management implications of these results are presented.