The impact of ocean warming on selected commercial fisheries in New Zealand

Warming oceans affect the growth, reproduction and location of fish species. Using a bioeconomic framework, we estimate the relationship between sea surface temperature (SST) and the catch of de facto open-access commercial fisheries of flatfish, trevally and jack mackerel in New Zealand. Assuming either a logarithmic or quadratic relationship between the SST and the carrying capacity of the fish stock, we consider three fishing methods (bottom trawl, set net and midwater trawl) and two measures of effort (count and duration). We show that ocean warming results in an increase in catch for all species if we assume a logarithmic relationship, with the highest marginal product of SST (${\mathrm{MP}}_{\mathrm{SST}}$) for jack mackerel caught using midwater trawl. The highest marginal revenue product (computed by the MP_SST, current price and fished area) is found for flatfish caught by set net. However, when assuming a quadratic relationship, there is a threshold above which catch starts to decrease, with the maximum catch of species ranging between 10 and 12.2°C. These results also vary spatially, with higher values of MP_SST observed in areas closer to the South Pole. Our findings are relevant for any review of fisheries management systems in response to ocean warming.