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 off any New Zealand coast, they are most frequently seen in the Bay of Islands, the Hauraki Gulf, Tasman Bay, Golden Bay and Fiordland.
- The Trust sponsors a long-term research programme on Fiordland bottlenose dolphins
- The Doubtful Sound population has declined substantially since the study began in 1990
- Calf survival is 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 fishing
- Small dolphin protection zones provide some protection from tourism
- Tourism guidelines are currently voluntary
- The ecological impacts of the power station could be reduced by releasing smaller amounts of cold freshwater into Doubtful Sound in winter and early spring
New Zealand’s bottlenose dolphins, particularly those in the far south, are among the largest bottlenoses 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 – restricted to spring and summer. The timing of births is really important. Our latest research has shown that calves born early or late in the calving season have a much lower chance of survival. Calves are totally dependent on their mothers for the first six months, and become progressively independent over the next two 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. By contrast, in summer they favour the inner regions, which at that time 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.
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. This long-term study that has uncovered some uncomfortable facts.
Our most important work showed that this population has been in serious decline. The Doubtful Sound population gradually declined from 69 in 1994 to 56 in 2006. The decline was due to a sudden change in calf survival, which halved in 2002 and has stayed low. Calf survival in this population is the lowest of any bottlenose dolphin population. Lower even than calf survival in captivity.
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.
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 clear impacts on the dolphins’ behaviour. While juveniles are often attracted to the boats, the adults, especially females with calves, usually avoid them. Mothers and calves usually avoid boats by “slinking” along the fiord walls or diving for longer. These reactions are most obvious when skippers ignore the rules imposed by the Marine Mammal Protection Regulations, approaching at speed, or head-on. Thankfully, skipper behaviour has improved, and the companies now follow a code of practice designed to reduce impacts.
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.
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.
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