Update on New Zealand dolphins and fisheries
Elisabeth Slooten, Stephen Dawson, Thomas Brough
New information on dolphin distribution and the spatial distribution and intensity of fishing effort was used to provide Kernel Density maps of dolphins and fishing effort. Considerable overlap remains between NZ dolphins and fishing methods that cause dolphin mortality (gillnets and trawling). Bycatch is highly clustered and has had a strong influence on current dolphin distribution. To date, line-transect population surveys have been of insufficient intensity to adequately assess abundance in low density areas. Bycatch is also difficult to detect, especially in small dolphin populations, due to very low observer coverage (typically below 5%). Taken together, these two factors make it difficult to accurately estimate risk for small populations of NZ dolphins, including the North Island subspecies Maui dolphin. Insufficient information is available about other potential threats to NZ dolphin, including pollution, marine mining and disease, to quantify their impact. At this time, bycatch is the only impact for which the level of mortality is quantifiable and for which an effective solution is available. Over the last 40 years, high levels of fishing effort and overlap between dolphins and fishing have caused a substantial population declines and population fragmentation. In two populations, Maui dolphin and the Hectorâ€™s dolphin population at Banks Peninsula, an increase in survival rate has been detected following partial protection.