Recreational fishing effects on New Zealand abalone (pāua, Haliotis iris) after five years of fishery closure: a matrix-based approach

New Zealand has one of the few remaining wild harvest abalone fisheries in the world. The commercial and cultural sectors of the fishery are well-regulated using enforceable catch allocations and reporting, but the recreational fishery has no requirements for catch reporting. The effects of the recreational fishery on population growth and stability are therefore largely unknown. Here, we use a stage-based matrix model to evaluate shore-based recreational fishing pressure on abalone following a five-year earthquake-driven fishery closure along the northeast coast of New Zealand's South Island. Data underpinning model parameters were obtained from published field surveys, which were collected throughout the five-year closure and immediately after the fishery re-opened from fished sites and non-fished control sites. The model showed that populations grew 6 % year^-1 (λ = 1.06 ± 0.28) during the fishery closure. After re-opening, however, the population growth rate decreased rapidly to -13 %, (0.87 ± 0.32) due to extreme fishing pressure; the estimated recreational catch exceeded the allowance by nearly 9x (∼42t catch vs. 5t allowance). The model also showed that if the five-tonne allowance been enforced, the population would have continued to grow at 4 % year^-1 (λ = 1.04 ± 0.28). Current management practices create significant sources of uncertainty for the long-term stability of this iconic fishery. Considering potentially significant effects that the recreational fishery has on the population growth rate, we would recommend a more conservative approach to management and mandatory catch-reporting requirements, which would allow populations to respond better to increasing pressure and potential effects of future climate variability.