Impacts on CPUE from vessel fleet composition changes in an Australian lobster (Jasus edwardsii) fishery

The Australian Victorian Western Zone rock lobster fishery is assessed using standardised catch-per-unit-effort (CPUE). Nominal CPUE declined over 1978–2009, but this underrepresents the estimated decline in abundance, and since 2009 standardised CPUE rose notably less than nominal CPUE. This study identified vessel as a key factor that explains the discrepancy between nominal and standardised CPUE. The composition of the fleet changed since 2009, under the pressure of constraining total allowable catch quotas, with vessels exiting the fishery having substantially lower estimated catchability, which increased the average catchability of the remaining fleet. New diagnostic indices were constructed to quantify discrepancies between trends in nominal and standardised CPUE that assisted in identifying periods during which both catchability and fleet composition changed.