Balancing act for Hector’s dolphins

Rob Mattlin and Rob Murdoch describe the continuing conflict between conservation and fisheries in New Zealand waters.

Hector’s dolphins are caught in a net of increasing demands for New Zealand’s marine environment. Commercial and recreational fishing, aquaculture, mining, oil and gas extraction, tourism, and recreational use all lay claim to the sea. The pressure of these demands is especially evident in coastal waters, the region of greatest competition between commercial, traditional, and recreational users. Managing these varied pressures on the environment is challenging, particularly when they affect highly mobile species, such as fish, seabirds, and marine mammals. A coastal species especially vulnerable to human pressures is Hector’s dolphin, along with its closely related subspecies, Maui’s dolphin.

Unique New Zealand natives

Among the smallest and rarest cetaceans in the world, these dolphins are found only in New Zealand. Hector’s dolphins are relatively small, averaging 40–60 kilograms and 1.2–1.6 metres long. Their bodies are light grey with black and white markings, and their distinctive rounded dorsal fin has been compared to Mickey Mouse’s ears. The greatest threats to their survival are incidental catch in commercial and recreational inshore set-net fisheries and, to a lesser degree, commercial trawl fisheries.

Just how many Hector’s dolphins there were before the introduction of monofilament set nets in the early 1970s is open for debate. What is apparent, however, is that Hector’s dolphin numbers have declined significantly; some research suggests that less than a third of the original population remains. There are thought to be fewer than 8000 today.

Sanctuaries to preserve and protect

In an effort to halt the decline in dolphin numbers, the Department of Conservation (DOC) established the first marine mammal sanctuary for Hector’s dolphins in Banks Peninsula in 1988. It covered an area of 1140 square kilometres, and extended from Sumner Head to the Rakaia River and out to a distance of 4 nautical miles from land. In 2008, the boundaries were extended along the coast and out to 12 nautical miles from the coast, encompassing an area of about 4130 square kilometres. This increase was in response to the continued decline of Hector’s dolphins through set-net bycatch and was enacted to further protect the Banks Peninsula dolphin population.

Later that year, DOC established four additional marine mammal sanctuaries to help protect Hector’s and Maui’s dolphins in other parts of New Zealand. These were located off the west coast of the North Island, from Northland to Taranaki; Clifford Bay and Cloudy Bay in Marlborough, Porpoise Bay on the Catlins Coast, and Te Waewae Bay on the south coast of the South Island. The sanctuaries established restrictions on mining and acoustic seismic surveying, activities known to damage dolphin habitat and disrupt their natural behaviour.

The protection offered by these new sanctuaries was complemented by new fishing measures introduced by the Minister of Fisheries. While all methods of fishing are allowed within the sanctuaries, in most of the areas off the east coast of the South Island set nets are prohibited within 4 nautical miles of the shore. For a number of commercial fishers, however, the new fishing restrictions put their livelihoods at risk: they expected to lose millions of dollars of revenue as a result. Iwi were also concerned that the new measures imposed unnecessary substantive restrictions on their ability to use their fisheries settlement assets, commercially and recreationally.

The fishing industry sought interim relief from the restrictions through a judicial review based on these concerns; as a result, set-net fishing has been allowed to continue for butterfish within some of the exempted areas. The fishing restrictions in these areas are now being reconsidered by the Minister of Fisheries. The challenge is to find management solutions that protect both the dolphins and the fisheries. Such solutions will require a much better understanding of the dolphins’ distribution, range, movement, and use of habitat.

Fine-tuning the regulations

The tragic result of an encounter with a set net. [Supplied by Department of Conservation]

While much is known about the biology and behaviour of these animals, there is much yet to be discovered. We do know that many Hector’s dolphin subpopulations show a distinct seasonal movement offshore during winter and onshore during summer. This pattern was highlighted during a recent NIWA survey of Hector’s dolphins in Clifford Bay and Cloudy Bay. These aerial surveys, which took place every three months for three years, indicated that about 900 dolphins used the bays in the summer, decreasing to fewer than 200 during late winter and early spring.

Some contend that the dolphins did not move far from the bays, and that they were within a few nautical miles of the bays year-round. While this may be true for some of the animals that use Clifford and Cloudy Bays, an unknown percentage may be travelling a considerable distance from the area, perhaps as far as the east coast of the North Island, towards Kaikoura, into the Marlborough Sounds, or elsewhere.

Uncertainty about the year-round whereabouts of these and other subpopulations raises some key questions: can the current marine mammal sanctuaries protect the dolphins, and do we need a more flexible approach to fishing restrictions? For example, restrictions might be applied seasonally based on the dolphins’ movements.

A new project at NIWA will help solve the riddle of where some of the Clifford Bay and Cloudy Bay dolphins may be going during the winter. Hector’s dolphins are included in a research programme funded by the Foundation for Research, Science and Technology to determine the movement of rare fish, seabirds, and marine mammals. In this study, scientists will fit up to ten dolphins with a satellite-linked transmitter that records the location of the instrument (and the animal) through the Argos satellite system.

Mapping to resolve conflict

The results from the proposed satellite-tagging project will help to develop models of coastal habitat use by the animals. By combining these models with information on known threats and risks (such as set-net fishing, mining, and acoustic surveying), NIWA scientists will be able to design GIS maps showing areas of conflict that require protection, and areas of non-conflict that can potentially be open to activities such as fishing. The dynamic nature of the maps will foster a more flexible approach to management, taking into account seasonal changes in dolphin distribution and resource use. The goal of this project is to reduce conflicts between people and marine mammals and improve management of multiple-use marine areas. It will help find the balance between potential economic benefits – such as fisheries, aquaculture, and mining – and conservation of an iconic species.

Written by Dr Rob Mattlin, a marine mammal consultant, and Dr Rob Murdoch, NIWA's General Manager, Research.

Dolphin. [NIWA]