Bottlenose dolphins are found in most of the World’s coastal areas.

Of the dolphins, only killer whales (which really are dolphins) have a wider distribution. While bottlenose dolphins can been seen all over Aotearoa-New Zealand, they are most frequently seen in the Bay of Islands, the Hauraki Gulf, Tasman Bay, Golden Bay and Fiordland.

Key Points

• The Trust, in collaboration with the Department of Conservation, sponsors a long-term research programme on Fiordland bottlenose dolphins
• The Doubtful Sound population has experiences periods of decline since the study began in 1990
• Calf survival has been lower than in any other bottlenose dolphin population, including bottlenose dolphins in captivity
• Potential causes for the very low calf survival include tourism, direct and indirect effects of freshwater input from the Manapouri Power Station, and the long-term, ecological effects of anthropogenic pressures (i.e. fishing and climate change)
• Dolphin protection zones provide some protection from tourism
• Tourism guidelines are currently voluntary

Biology

New Zealand’s bottlenose dolphins, particularly those in the far south, are among the largest of the species in the world, reaching almost four metres in length, and weighing as much as a medium-sized horse. They are stocky – which is typical of cold water populations.

Bottlenose dolphins reach sexual maturity between 7 and 12 years old. Mature females give birth to a single calf every 2-4 years. Maximum lifespan is at least 40 years. In Fiordland, births are highly seasonal with most births observed between the spring and summer. Our research has shown that the timing of births is important as calves born early or late in the calving season have a much lower chance of survival. Calves are dependent on their mothers for the first six months, and become progressively independent over the next several years.

In Doubtful Sound, our studies have shown that the resident dolphins have a much more stable society than elsewhere. Ties within the group are strong and long-lasting. This is unusual among dolphins, which, except for mothers and calves, typically have more casual social ties. Strong bonds in this community may be due to the habitat. Fiordland is almost as far South as bottlenose dolphins go. It may be that these dolphins need to co-operate more to survive near the limit of their distribution.

It is clear that the cold of Fiordand is an important factor in where the dolphins go. In the coldest months, the dolphins avoid the extremely cold inner regions of the fiord, but are often sighted there in the summer when the inner regions are warmer.

Bottlenose dolphins are incredibly adaptable. Ultimately, that’s why they are so widely distributed – they can modify their behaviour to adapt to almost any circumstance. Whether it is herding fish against the side of a boat, or beating their tail against a muddy bottom to create a visual barrier, these dolphins are capable of extraordinary co-operation to catch elusive prey.

Conservation problems

New Zealand Whale and Dolphin Trust sponsorship has been instrumental in continuing a long-term research programme on the Doubtful Sound dolphins. For over 20 years, researchers have studied their habitat use, ecology, behaviour and population trends and the impact of tourism.

Our work has shown that the population has experienced periods of decline including in the early 2000s. The decline has been attributed to a sudden change in calf survival, which halved in 2002 and has stayed low.

Potential reasons for the extremely low level of calf survival include tourism, ecological impacts of long-term fishing within the fiords and ecological and/or direct impacts of freshwater discharge from the Manapouri power station.

Tourism:

The unique beauty of Fiordland supports a lucrative tourism industry. The dolphins, of course, are a key attraction. Even though the levels of tour boat activity are relatively low, in Doubtful Sound these activities can have impacts on the dolphins’ behaviour. These reactions are most obvious when skippers ignore the rules imposed by the Marine Mammal Protection Regulations, approaching at speed, or head-on. Thankfully, vessel behaviour has improved, and the tourism companies follow a code of practice designed to reduce impacts.

Power Generation:

A local power station takes water from Lake Manapouri, runs it through hydro-electric turbines and then disposes of the water into Doubtful Sound. The height difference between the lake and the fiord makes this a very efficient power station. The problem is, the water can be much colder than the ambient temperature of Doubtful Sound, especially in winter and spring. This is an important time for the local dolphin population. The females go through the final stages of pregnancy in winter and give birth in spring. The young calves have to keep their own bodies warm for the first time, and are at their physiological limits. Cooler water temperatures at this time are a challenge. Add to that potential stress from approaches from tour boats and the relatively low food availability in the fiords, which are still recovering from the impact of past intense fishing pressures. We are not yet sure which of these human impacts are most critical and how the combined effect of several human activities affects the dolphins. This is the focus of our continued research.

Solutions

Research funded by the NZ Whale and Dolphin Trust has been crucial in the development of the current protection measures. Our research has raised the profile of these dolphins’ conservation problems, both nationally and internationally, to help them get the protection they need.

Dolphin Protection Zones have recently been created, in areas that our research showed to be most frequently used by the dolphins. These are a step in the right direction. The protection zones extend 200m from the shoreline, in the areas indicated in red on the map below. Boats are allowed to enter these areas for fishing, diving, anchoring etc. Voluntary guidelines request that boats travel at a slower speed (5 knots) than elsewhere in the fiord, and do not enter Dolphin Protection Zones if dolphins are seen.

Protection of the Doubtful Sound dolphins could be improved by further reducing the effects of tourism and other human impacts. For example, by increasing the size of the Dolphin Protection Zones and turning the voluntary guidelines into regulations. The amount of freshwater input into Doubtful Sound could be reduced, especially in late winter and early spring which are critical times for dolphins in the final stages of pregnancy and newborn calves. Young calves are especially vulnerable to human impact. We are interested in determining how effective these measures are.

Research Papers

Bottlenose dolphins