Abstract
Tourism targeting cetaceans near Kaikoura, New Zealand began in the late 1980s and five commercial operators offer tours to swim with or view pods of dusky dolphins. These dolphins are part of a large, mobile population of dusky dolphins found around the southern New Zealand coast. The New Zealand Department of Conservation commissioned a study in the mid-90s (Barr and Slooten 1999) examining the effects of tourism on dusky dolphins, and placed a 10-year moratorium on new permits. This study was designed to evaluate the short- and long-term effects of tourism on dusky dolphins by collecting current data and comparing it to data collected by previous researchers. It was also timed to provide further recommendations for management of this activity at the end of the 10-year moratorium.
Focal group follow methods were used to track movement and behaviour of large pods of dusky dolphins from a shore station, and the number of water entries (swim drop) and length of time swimmers spent in the water were collected onboard tour vessels. Behaviour and movement of dusky dolphins was variable by season and time of day, sophisticated analytical techniques accounted for this variability and described responses of dolphins to vessels. Dolphins spent less time resting and socialising and more time milling when vessels were present. Bout lengths for all behavioural states except milling were significantly shortened in the presence of vessels. Group swimming speed slowed as the number of vessels present grew, and all leap types except porpoising increased. The magnitude of changes grew as the number of vessels present rose, but was not highly dependent on vessel type. More than three vessels were present in 2.0% of observations. During the midday rest period, vessels were within 300 meters of dolphins 25.8% of observations. When the number of swim-tour vessels increased from two to three, there was a significant increase in the number of swim drops required and a corresponding significant decrease in the length of each swim drop.
Comparison with data collected by other researchers indicated that responses of dusky dolphins to tourism vessels have grown over time, from prior to the advent of tourism (1984-1988), during the growth of tourism (1993-1999), until the present (2008-2010). Resting has significantly decreased, while milling has increased. Group swimming speeds have decreased. No large-scale habitat shift has occurred, though there may be fine-scale shifts toward shallower water and southward.
Responses of dolphins have grown in magnitude, an indication that the animals are less tolerant of vessel traffic than in the past. Because this study examined group behaviour, it is not clear if lowered tolerance is due to individual sensitisation, disinterest, or a general response to increased boat traffic. The potential short-term effects of the reported responses include changes in energy expenditure (positive or negative), reduced ability to communicate, displacement from preferred habitat, and increased exposure to predators, but it is not apparent that any of these effects are occurring. Chronic exposure to disturbance has been linked to habitat displacement and reduced reproductive success in bottlenose dolphins, so the results described here indicate there is potential for population-level impact on dusky dolphins. Research into the mechanism of disturbance is proposed, to determine whether acoustic masking of dolphin vocalisations is occurring. The physiological effects of behavioural changes must also be investigated. The energetic cost of changes in behavioural state should be quantified, and research is needed to determine if stress hormone levels increase in the presence of tourism vessels. In order to determine if reproductive success is affected by vessel traffic, individual levels of exposure must be quantified, and correlated with pregnancy and birth rates. Better population estimates are needed to evaluate whether population-level effects are occurring, and aerial survey work around New Zealand is needed. Local abundance near the tourism area should also be tracked to see if habitat displacement occurs.
Limits of Acceptable Change (LAC) were initially developed to manage visitor numbers within the national park system in the United States. Managers recognised the ecological impact that large numbers of visitors had on the park, and devised a system which established limits which would allow the maximum number of visitors but not degrade the resource. This system was adopted by wildlife managers, and is dependent upon setting threshold LAC parameters which are based on measureable limits of change. The work proposed above is needed to establish meaningful levels at which biologically significant change occurs. These threshold values should be established as the (LAC) for management of this activity. A consistent 5-year cycle should also be set for re-evaluation of responses of dusky dolphins relative to the LAC criteria. Annual data collection should be established to continue building the long-term time-series data needed to evaluate LAC criteria. Shore-based observations of tourism vessels should be used to enhance monitoring of operations for compliance with regulations. In 2010, changes to permit conditions were instituted which included limits on the number of swim drops per tour, an increase in the number of swimmers allowed per tour, and mandatory observance of the midday rest period. If these changes do not succeed in reducing vessel traffic near dusky dolphins, managers must consider reducing the number of commercial permits or the number of vessels allowed within 300 meters until appropriate LAC criteria are established.