9781888569605-ch123

Benthic Habitats and the Effects of Fishing

Symposium Abstract: Deepwater Trawl Fisheries Modify Benthic Community Structure in Similar Ways to Fisheries in Coastal Ecosystems

M. Cryer, B. Hartill, and S. O’Shea

doi: https://doi.org/10.47886/9781888569605.ch123

Off north-eastern New Zealand, the Bay of Plenty continental slope supports bottom trawl fisheries for gemfish Rexea solandri, hoki Macruronus novaezelandiae, tarakihi Nemadactylus macropterus, and, most recently scampi (a burrowing, deep-water lobster, Metanephrops challengeri). Excellent information has been collected since 1988 on the distribution of trawling effort in these fisheries, including the start and finish location of each trawl tow with a precision of 1 minute of latitude and longitude. Using a GIS, we linked these data to information on the invertebrate bycatch of 66 research trawls, and explored the extent to which the composition of our bycatch (as one index of benthic community structure) could be explained by the frequency of trawling at a given site. Using multivariate ordination techniques, we explained up to 65% of variation in the distribution of species among samples, more than half of which was attributable to our indices of trawling (mainly for scampi and gemfish). Qualitatively, the inferred effects of deep-water trawling were similar to those of coastal fisheries; increasing fishing activity was associated with reductions in species richness, diversity, and the abundance of large or fragile taxa. The gross quality of information on fishing effort has hitherto been a major constraint on our understanding of the effects of fishing. This study is one example of the way good quality information at the right (fine) scale can further that understanding, but comprehensive information on the distribution of fishing effort may also allow extrapolation of experimental studies to the wider scale of fisheries management.