Other threats are being struck by boats, having their habitat affected by pollution and coastal development, and exploration for oil and gas.
These dangers have taken a huge toll on Hector’s dolphins since the 1970s. Scientists estimate their population back then was more than 26,000, more than three times the current estimate of around 7000.
Deaths in fishing nets
People with fishing interests often claim dolphin bycatch is not an issue because official records report few dolphin deaths – an average of just 2 dolphins a year.
However, official records are based on reports voluntarily made by fishers – there are no independent observers involved.
Experience for other bycatch species, such as sea lions, shows that voluntary reporting is less than accurate, with under-reporting of deaths and injuries. In 2004, a report prepared for the Ministry of Fisheries said fishing vessels that don’t have government-funded fisheries observers on board consistently report far fewer seabird catches than those that do have observers.
The same is true for Hector’s dolphins, as shown by the National Institute of Water and Atmospheric Research (NIWA). NIWA used data from independent observations to develop a credible estimate of around 30 Hector’s dolphin deaths a year in the Canterbury gill net fishery – 28 more than the fishing industry voluntarily reports, on average.
A 2008 NIWA risk analysis, prepared for the Ministry of Fisheries, estimates the total New Zealand death rate at 110-150 Hector's and Maui's dolphins every year.
This figure is the most accurate scientific estimate available. Clearly the number voluntarily reported is the tip of the iceberg.
The dolphins’ future is simple. The fishing industry needs to begin fishing in ways that don’t kill dolphins. More than anyone else, the future of Hector’s and Maui’s dolphins lies in their hands. There is a precedent – parts of the fishing industry are working with government and conservation organisations to reduce seabird bycatch – it’s time to do it for dolphins.