Behavioural effects of tourism on oceanic common dolphins, Delphinus sp., in New Zealand: the effects of Markov analysis variations and current tour operator compliance with regulations

Abstract

Common dolphins, Delphinus sp., are one of the marine mammal species tourism operations in New Zealand focus on. While effects of cetacean-watching activities have previously been examined in coastal regions in New Zealand, this study is the first to investigate effects of commercial tourism and recreational vessels on common dolphins in an open oceanic habitat. Observations from both an independent research vessel and aboard commercial tour vessels operating off the central and east coast Bay of Plenty, North Island, New Zealand were used to assess dolphin behaviour and record the level of compliance by permitted commercial tour operators and private recreational vessels with New Zealand regulations. Dolphin behaviour was assessed using two different approaches to Markov chain analysis in order to examine variation of responses of dolphins to vessels. Results showed that, regardless of the variance in Markov methods, dolphin foraging behaviour was significantly altered by boat interactions. Dolphins spent less time foraging during interactions and took significantly longer to return to foraging once disrupted by vessel presence. This research raises concerns about the potential disruption to feeding, a biologically critical behaviour. This may be particularly important in an open oceanic habitat, where prey resources are typically widely dispersed and unpredictable in abundance. Furthermore, because tourism in this region focuses on common dolphins transiting between adjacent coastal locations, the potential for cumulative effects could exacerbate the local effects demonstrated in this study. While the overall level of compliance by commercial operators was relatively high, non-compliance to the regulations was observed with time restriction, number or speed of vessels interacting with dolphins not being respected. Additionally, prohibited swimming with calves did occur. The effects shown in this study should be carefully considered within conservation management plans, in order to reduce the risk of detrimental effects on common dolphins within the region.

Figure 1. Study area.

Location of the Bay of Plenty (BOP) and other places referred to in the text in relation to the North and South Island of New Zealand.

Figure 2. Effect of vessel interactions on the behavioural budget of common dolphins in the Bay of Plenty.

Proportion of time spent in each behavioural state in the presence and absence of interacting vessels. Error bars represent 95% confidence intervals. Significant differences (p<0.05) between control (solid or striped black bars) and interaction scenarios (light and dark grey bars) are denoted by an (*). Results are shown following the conservative and less conservative approaches. Note: FOR = foraging, MIL = milling, TRA = travelling.

Figure 3. Effect of vessel presence on transitions between behavioural states of common dolphins, based on differences in transition probabilities(p_{ij (interaction)}-p_{ij( control)}).

A negative value means that the behavioural transition of the control chain is superior to that of the interaction chain. The graph is composed of three parts, one for each preceding state, separated by vertical lines. In each part, bars correspond to succeeding behavioural states (see legend). Transitions with a significant difference (p<0.05) are marked by an (*). Results shown after following the conservative approach (c) and the less conservative approach (lc). Note: FOR = foraging, MIL = milling, TRA = travelling.

Figure 4. Effect of vessel traffic intensity on dolphin behaviour.

a) P-values of the difference between the cumulative behavioural budget and the control behavioural budget for common dolphin activity. The proportion of time dolphins spent with interacting vessels was artificially varied from 0 to 100%. Each curve corresponds to different behavioural states (FOR = foraging, MIL = milling, TRA = travelling). The horizontal dashed line represents the statistical level of significance (p<0.05) b) Vessel traffic intensity throughout the study period (November 2010 to April 2013). The horizontal dashed lines represent 34.0 and 56.0% of traffic intensity above which the cumulative foraging and travelling behaviours, respectively, are significantly affected. The vertical lines separate the tourism and non-tourism seasons.