Globally, mitigation has focused on four main techniques: acoustic deterrents; spatial and temporal closures; gear modifications and operational modifications. Over half of the literature reviewed was related to acoustic deterrents, over a quarter spatial and temporal closures, and the remainder split between gear and operational modifications.
In general terms, studies of the techniques tended to provide inconsistent and sometimes conflicting results regarding mitigation of protected species bycatch. These results varied by the protected species, the location of the fishery, the way the fishery operates and the time of year. Almost all mitigation techniques involved a trade-off between a reduction in bycatch and impact on the fishery.
Of the techniques reviewed, spatial and temporal closures, and acoustic deterrents (i.e. pingers) have themost research potential for application to New Zealand set net fisheries. While pingers have shown to behighly effective in some fisheries overseas, studies indicate they are unlikely to be effective for coastal delphinids, including Hector’s and Maui’s dolphins and other protected species in New Zealand. In contrast,there is excellent evidence of the effectiveness of spatial and temporal closures in reducing bycatch levels for all protected species investigated, when applied at an appropriate scale. This technique should, therefore, be most effective in reducing the bycatch of protected species in set nets in New Zealand. In order for spatial and temporal closures to be effective, however, they must be driven by clear, management goals for both protected species and fisheries, and be thoroughly evaluated against them.
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This report was commissioned by the Department of Conservation, Project MIT2012-03
By S. Childerhouse, E. Miller, and V. Steptoe