Is bottom trawling the most destructive method of fishing? Evidence from New Zealand’s commercial fisheries

In New Zealand, fisheries are managed by the Individual Transferable Quota (ITQ) system which limits the total catch to a biologically sustainable quota and secures individuals a tradable portion. The incentives to quota holders are to use the most efficient fishing methods, of which bottom trawling is widely perceived as the most destructive. Regulations aim to reduce the effects of destructive fishing methods, however, no quantitative studies exist to examine how effective these are. We merge a comprehensive dataset of catch and effort between 2011 and 2021 with a manually assembled dataset on the exploitation status of 115 ITQ fish stocks in New Zealand to estimate the impact of fishing method on sustainability. Our results show that a 10 percentage point increase in the share of midwater trawling has, by far, the biggest impact, leading to a cumulative increase of 17.79% percent in the probability of overexploitation. Against all expectations, bottom trawling has no statistically significant effect, while bottom longlining increases the probability by 5.57%. These results are in line with recent legislative changes in New Zealand that aim to mitigate the impacts of bycatch from midwater trawling and studies like this can be useful in monitoring their effectiveness.