A major international conference on marine mammals in Dunedin this week has focused attention on efforts to halt the extinction of Maui’s dolphin, a subspecies unique to New Zealand waters.
The Science Media Centre rounded up answers to questions aboutthe charismatic creature’s chances for survival from visiting speakers and participants in the event.
Dr Barbara Taylor, Leader, Marine Mammal Genetics Group, U.S. National Oceanic and Atmospheric Administration (NOAA), keynote speaker at the Society for Marine Mammalogy conference in Dunedin, comments:
With Maui’s dolphin numbers so low (12-15 breeding females) do they have a realistic chance of survival? Are there any examples of other marine mammals that have recovered from such low numbers?
“Maui’s can recover and other marine mammals have done so. Northern elephant seals are the most famous example having gotten down to a few tens of animals and now recovered into the hundreds of thousands. The recovery of Maui’s would be slower and may involve losing its identity as a subspecies if recovery involves recruitment from Hector”s dolphin. Several Hector’s dolphins have been documented in Maui’s dolphin range with no interbreeding yet. But that may happen and it may be a necessary rescue.”
What will it mean if we lose Maui’s dolphin? When would we know they are extinct?
“It could mean that a subspecies found only on New Zealand’s north island will be truly gone or it could be that the north island will be recolonized by Hector’s dolphins. Only time will tell. It is hard to prove extinction. The Chinese river dolphin, or baiji, remains listed as ‘presumed extinct’ although none have been seen since 2003 despite exhaustive searches. Caribbean monk seals were just recently officially listed as extinct even though the last confirmed sighting was in the 1950s. It will be even harder with Maui’s dolphin because you can’t tell them apart from Hector’s dolphin in the wild and we know that a few Hector’s dolphin have recently been found in north island waters as confirmed by genetics.”
How important is fishing vs. other causes of death like disease (e.g. toxoplasmosis) for Maui’s?
“Fishing is THE threat. Every other threat is not worth considering at this point.”
In your view, could the effort, resources and political goodwill directed at saving Maui’s dolphin be potentially better spent on other pressing marine conservation issues?
“In my view, it is very important for New Zealand to seize this opportunity to show the world how to save a small dolphin from coastal fishing efforts. There are many similar cases around the world including vaquita, a small porpoise only found in a small area in Mexico. If a rich country like New Zealand can’t save it’s coastal species then that serves as a very bad example to many countries with many fewer resources. We may be fated to lose coastal dolphins in most of the world coasts unless people solve this problem of killing these beautiful animals because the choose a fishing method that does so. Fishing can continue with alternative gears that may cost the consumer a bit more but if people want their children and grandchildren to enjoy dolphins that they can see from the beach, this is the price we must pay.”
Prof Steve Dawson, Marine Science, University of Otago, comments:
“Maui’s dolphins have a chance of survival if we are brave enough to remove the fisheries that kill them from within their range. That means excluding gill netting and trawling from Maui’s dolphin habitat. There would be no need for restrictions on any other fishing methods.
Are there any examples of other marine mammals that have recovered from such low numbers?
“Not to my knowledge. This underscores the urgency of acting NOW.”
What will it mean if we lose Maui’s dolphin? When would we know they are extinct?
“Ecologically, we know that top predators can have very important roles in marine systems. In some cases their removal has radically changed the case of Maui’s dolphin, because they are so rare now that their ecological effect is probably small.
“It will mean that NZ has lost a marine mammal subspecies. That this could happen, in a developed country with a strong conservation history, is shameful.
“Time to extinction is impossible to predict precisely, because at very small population sizes the differences among individuals (for example some will be good breeders, some poor) become very important. The current rate of decline is 3% per year. Normally, when population size gets very small, the rate of decline accelerates dramatically. Unless this is reversed, extinction in anything between 20-100 years is likely.”
How important is fishing vs. other causes of death like disease (e.g. toxoplasmosis) for Maui’s?
“In my opinion, far more important. All modelling of future population trend has included only the effects of fisheries. In other words, Fisheries impacts, by themselves, are sufficient to explain the sort of decline that we see. This is not to say that there are other impacts. Disease can be very important, especially at very small population sizes. However, wildlife populations have evolved to deal with disease. They have not evolved to deal with impacts caused by human technologies.”
In your view, could the effort, resources and political goodwill directed at saving Maui’s dolphin be potentially better spent on other pressing marine conservation issues?
“Saving Maui’s dolphins need not cost much. We need only to stop using entangling fishing methods (i.e. gill netting and trawling) in their range. Other fishing methods are fine. Because captive management is not practical, this problem must be managed at sea.
“We need to remember that reducing fishing pressure in Maui’s dolphin habitat will have very positive long-term benefits FOR THOSE FISHERIES. Rebuilding those fish stocks will make it easier to catch fish. Fishing methods that are less damaging (e.g. long lining) will become more economically feasible in this area.”