27 March 2012


Hector's dolphin. Credit: James Shook via Wikimedia Commons.
A new study provides the first empirical evidence that a marine protected area (MPA) has robustly improved the survival of a marine mammal. In this case, one of the world's most endangered marine mammals, the Hector's dolphin (Cephalorhynchus hectori) of New Zealand.
The IUCN Red List describes the problems facing this diminutive cetacean:
This species is considered to be Endangered due to an ongoing and projected decline of greater than 50% over 3 generations (approx. 39 years)... Hector’s dolphin has the most limited range of any marine cetacean other than the vaquita (Phocoena sinus)... The main cause of population decline is ongoing bycatch in [gillnet and trawl] fisheries.
Concerned for the future of this rare species (population: 7,270 individuals), New Zealand in 1988 established the Banks Peninsula Marine Mammal Sanctuary in 1,170-square-kilometers (451-square-miles) of waters off the South Island. 

Banks Peninsula, South Island, New Zealand. Credit: NASA Astronaut Photo ISS013-E-67242.

The research, ongoing since 1986, involved identifying 462 individual Hector's dolphins through photographs and then analyzing the photographic re-sightings using a Bayesian mark-recapture technique. The team applied a population model to assess the impact of the MPA on the dolphins.

Their results show that since the designation of the sanctuary, the Hector's dolphins' survival rate has increased by 5.4 percent: 

  • From a decline of ~6 percent per year
  • Now slowed to a rate of decline of ~1 percent per year

As good as that sounds, the researchers were surprised survival rates hadn't increased further, since they expected the establishment of the MPA to solve the problem entirely.
Hector's dolphin. Credit: David Searle via Flickr.

Instead they discovered the dolphins don't spend the whole year in the sanctuary. Co-author Liz Slooten tells me:

Their distribution with respect to depth and distance offshore changes. In winter they are almost evenly distributed with respect to depth and distance offshore. In summer they are strongly concentrated close to shore. This means that in summer about 80% of the population is inside the sanctuary and protected. In winter this drops to only about 40%. Too many dolphins are still being caught in fishing nets to allow the population to stabilise, let alone recover from the massive decline they've suffered over the last three decades.

"The MPA hasn't quite yet 'saved' the dolphins," says Slooten, "but it's been a major step in the right direction. 
The take home message is that size matters. Marine Protected Areas work, but they have to be large enough in order to be effective."

The paper in early view at the Journal of Applied Ecology:

  • Andrew M Gormley, Elisabeth Slooten, Steve Dawson, Richard J Barker, Will Rayment, Sam du Fresne and Stefan Brager (2012). First evidence that Marine Protected Areas can work for marine mammals. Jour. App. Ecol. DOI: 10.1111/j.1365-2664.2012.02121.x
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