tursiops.org - Tourist boats destroying dolphin community

Conservation workers will seek increased protection for marine mammals in the pristine Doubtful Sound in Fiordland after the discovery tourist boats are destroying its unique community of bottlenose dolphins.

Fiordland is one of the most popular areas for eco-tourists coming to New Zealand, but a report released late yesterday revealed vessels in Doubtful Sound are hurting the viability of the dolphin population there.

"It is highly likely that the existing range and intensity of impacts will lead to the Doubtful Sound complex dolphin population becoming extinct within 45 years," said a report released by the Department of Conservation (DOC).

There were 69 dolphins in the Doubtful Sound community in 1994, but by 2006, that had dropped to 56, with more dolphins dying or being killed than were being born.

"This decline is one of the steepest ever recorded for a dolphin population that is not exposed to direct or indirect takes from fishing," said DOC, which has issued eight marine mammal "viewing permits" for the dolphins.

The Doubtful Sound dolphins remain in the fjord year-round – with most never leaving for more than a few hours – and they have distinctive social and cultural characteristics.

A study by Otago University marine ecologist David Lusseau's found that like other bottlenose dolphins, the Doubtful Sound males fought among themselves to win over female partners, but unlike similar dolphins in Florida and Australia, they refrained from forcing the females to have sex.

An earlier study he did from 1994-2000 revealed just a few genial dolphins keep dolphin societies together, and if they disappear, the social cohesion of the pod collapses.

His work illustrated that capturing wild animals – such as taking killer whales for display in marine parks – could have unforeseen consequences on their companions.

His body of work led to a broader understanding of the species that was thought to have highly sophisticated social relationships similar to humans.

Scenic cruises take place year round on vessels ranging from kayaks – usually in groups of five or six – to a 40m catamaran with twin diesel engines powered by twin diesel engines.

One company commissioned a giant glassed in boat to take up to 175 people at a time.

In summer eight operators focus their trips on Doubtful Sound, with one of then running two boats, Five of them run overnight or multi-night trips, and two only offer day trips.

Often, during summer, seven vessels and two kayaking groups – one with a support vessel are on the water each day during peak tourist season between December and March.

Some operators conduct tours in the fiord only during the winter.

Private recreational boats make up about 7.9 per cent of all dolphin-boat "interactions" within 400m of the dolphins – the distance at which they will tend to break off from a group when a boat approaches.

Dr Lusseau – who studied the Doubtful Sound dolphins from 1999 to 2002 – has shown some dolphins were diving for longer to avoid boats.

"Dive intervals were significantly longer when boat were present," the DOC report said

His study showed 70.6 per cent of dolphin-boat interactions violated the Marine Mammal Protection Regulations, and DOC said responses to boats had a significant energy cost "that females may find difficult to meet".

"Having to meet this cost could result in reduced reproductive success".

Between 1994 and 1999 – when there were stillbirths in two of the five years, they averaged 0.6 stillbirths a year, but between 2000 and 2006 this figure increased to stillbirths in five of the six years, to average 1.6 a year.

An Australian study in Shark Bay showed the reproductive success of females exposed to boat interactions was half the success of females not exposed to boats. The Australian Government's response was to halve the number of licences for dolphin viewing in the bay, to one.

Other threats were boat "strikes". In Milford Sound – where there are five times as many cruises as in Doubtful Sound – 7 per cent of Milford Sound dolphins bear scars from propellers and dolphins leave the fiord when there is too much traffic.

"The current level of surface water activity in the Doubtful Sound complex may already be too high for the resident population of bottlenose dolphins," DOC said.

Protection measures being considered in Doubtful Sound included no-boat zones, zones accessible by permit only, or where dolphin encounters may not be sought.

Commercial trip allocations could be cut, research limited, and permits or consents required for recreational boats. Speeds could be restricted, and skippers constrained from radioing the location of dolphins to other boats.

Source: http://www.stuff.co.nz/stuff/