Abstract
The increase in human activities off the coast of Kaikoura, New Zealand may be altering the behaviour and movement patterns of dusky dolphins (Lagenorhynchus obscurus). The primary aim of this research was to assess the influence of human activities on the movement patterns, behaviour and social groupings of dusky dolphins at Kaikoura. The secondary aim was to provide management recommendations to the Department of Conservation for dolphin watching and swimming operations. The main objectives were to: 1) document the exposure of dusky dolphins to human activities and 2) assess the short-term responses of dusky dolphins to boats and swimmers. The specific objectives were to: 1) determine if dolphins respond differently to different numbers and types of boats, 2) assess the levels of disturbance caused by these activities and 3) determine whether these activities affect dolphin behaviour differently depending on time of day.
I tracked dolphins and boats with a theodolite from a cliff top. I also recorded surface activity behaviour of the dolphins by visual scanning. I observed dolphins over 443 hours and 39 minutes from November 1993 to April 1995. At least one boat was present within 300 m of a focal dolphin pod for 72% of the total observation time. Of the 949
boat approaches observed, 84% were commercial dolphin or whale-watching boats, 10% were private boats and 6% were fishing boats. There was a significant increase in the number of commercial and private boats present with dolphins from 1994 to 1995.
Dolphins showed short-term changes in behaviour when boats approached within 300 m. In addition, there may be certain times of the day when dolphins are more susceptible to boat disturbance. This is most likely related to times when dolphins are normally resting. Aerial activity more than doubled in the presence of boats from late morning onwards; however, there was no statistically significant interaction between aerial activity and time of day. Dolphin pod dispersion was twice as high when boats were present during mid to late afternoon. There was no significant effect of the presence of boats and swimmers on dolphin pod dispersion, density, speed, number of directional changes and group envelope. There was also no significant effect of different numbers of boats on dolphin behaviour. Dolphins made more directional changes during midday and more clean leaps during late morning and midday when a combination of commercial boats with fishing and/or private boats were present. The significant effect of boat type and time of day indicates that dolphins may respond to boat behaviour and uncertainty in behaviour and that they are more susceptible to this disturbance later in the day. Dolphins responded to human activity with a noticeable change in behaviour 16 times. Reactions included faster swimming, increased aerial activity, startle reaction, and stopping, with dolphins moving in different directions. Most of these instances occurred when boats failed to abide by the conditions governing behaviour around dolphins as set out under the Marine Mammal Protection Regulations (1992).
There is a need for increased education of commercial skippers and the public on appropriate boating behaviour around dolphins. Making the behaviour of boats more consistent and predictable among commercial, fishing and private boats should reduce the effect of boat type on dolphin behaviour. A reduction in boat activity from late morning to the mid afternoon should also reduce disturbance.
There are no indications that boat activity has resulted in dolphins moving away from the Kaikoura area. Until data are available on the long-term and biological effects of dolphin watching on dusky dolphins, it would seem prudent to keep the amount of boat activity in the area at or below current levels. A precautionary approach, ensuring that boat disturbance does not increase will reduce the risk of potential long-term effects on the population.