New Zealand marine mammals and commercial fisheries

Citation

Berkenbusch, K., Abraham, E. R., & Torres, L. G. (2013). New Zealand marine mammals and commercial fisheries. New Zealand Aquatic Environment and Biodiversity Report No. 119. 104 p.

Summary

Incidental captures of marine mammals occur across different fisheries worldwide, affecting a range of cetacean and pinniped species. As bycatch assessments are often hampered by scarcity of data of the number and identity of captured individuals, risk assessments provide a systematic approach to identifying and evaluating potential impacts of fishing-related mortalities, while also accounting for uncertainty.

The present study forms the basis for a risk assessment of the interactions between different commercial fisheries and marine mammals in New Zealand waters. Considering the 35 marine mammal (sub)species that inhabit New Zealand waters, population data relevant to the risk assessment process were summarised for each of the 10 mysticetes, 22 odontocetes (including dolphins and beaked whales), and three pinnipeds. Existing bycatch data were used to characterise the different types of interactions between these marine mammals and trawl, longline, setnet, and pot/trap fisheries.

There were few bycatch records of baleen whales in New Zealand, with observed entanglements involving Bryde's, humpback and southern right whales. Data from other regions show that the majority of recorded bycatch incidents were entanglements and injuries in static gear, predominantly involving species and populations that reside in coastal waters. Although the New Zealand Bryde's whale population is resident in coastal northern North Island waters, the main threat identified for this species was not fisheries-related, but vessel collision, particularly in Hauraki Gulf.

For toothed cetaceans, bycatch documentation showed that direct interactions with fishing operations often lead to immediate mortality, particularly for small-sized dolphins, as captured individuals are unable to free themselves and drown in fishing gear. Furthermore, the coastal distributions of many dolphin species and their attraction to fishing vessels expose them to the risk of fisheries bycatch. Consistent with data from elsewhere, almost all toothed cetacean species have featured in bycatch reports in New Zealand, involving trawl, longline and gill/set-net fisheries. In addition to bycatch in trawl and gill/set-net fisheries, there have been documented Hector's dolphin entanglements in lobster fishing gear. Lobster pot gear has also been implicated in the bycatch of bottlenose dolphin and long-finned pilot whale in other regions.

For pinnipeds, trawl fisheries were the most significant source of mortality, with high numbers of New Zealand fur seal and New Zealand sea lion incidentally captured in these fisheries in New Zealand waters. New Zealand fur seal were also frequently bycaught in surface-longline fisheries. Data reviewed here led to the identification of different fisheries-marine mammal interactions, and will inform the next step in the risk assessment process involving marine mammals and commercial fisheries in New Zealand.