Behavioural Responses of Dusky Dolphin Groups (Lagenorhynchus obscurus) to Tour Vessels off Kaikoura, New Zealand

Abstract

BackgroundCommercial viewing and swimming with dusky dolphins (Lagenorhynchus obscurus) near Kaikoura, New Zealand began in the late 1980s and researchers have previously described changes in vocalisation, aerial behaviour, and group spacing in the presence of vessels. This study was conducted to assess the current effects that tourism has on the activity budget of dusky dolphins to provide wildlife managers with information for current decision-making and facilitate development of quantitative criteria for management of this industry in the future.Methodology/Principal FindingsFirst-order time discrete Markov chain models were used to assess changes in the behavioural state of dusky dolphin pods targeted by tour vessels. Log-linear analysis was conducted on behavioural state transitions to determine whether the likelihood of dolphins moving from one behavioural state to another changed based on natural and anthropogenic factors. The best-fitting model determined by Akaike Information Criteria values included season, time of day, and vessel presence within 300 m. Interactions with vessels reduced the proportion of time dolphins spent resting in spring and summer and increased time spent milling in all seasons except autumn. Dolphins spent more time socialising in spring and summer, when conception occurs and calves are born, and the proportion of time spent resting was highest in summer. Resting decreased and traveling increased in the afternoon.Conclusions/SignificanceResponses to tour vessel traffic are similar to those described for dusky dolphins elsewhere. Disturbance linked to vessels may interrupt social interactions, carry energetic costs, or otherwise affect individual fitness. Research is needed to determine if increased milling is a result of acoustic masking of communication due to vessel noise, and to establish levels at which changes to behavioural budgets of dusky dolphins are likely to cause long-term harm. Threshold values from these studies would allow managers to set appropriate operational conditions based on quantifiable criteria.

Estimating the cumulative effects of the nature-based tourism in a coastal dolphin population from southern Kenya

“…This suggests that dolphins responded to approaching boats at least 400m away, which is much further than the recommended minimum distance recommended by the dolphin tourism guidelines in KMMPA (100m). Boat interactions also led to a decrease in the resting bout length of dolphins, which has also been observed in other studies (Lundquist et al, 2012;Lusseau, 2003;Meissner et al, 2015;Stockin et al, 2008). Female dolphins are believed to mainly nurse their calves during resting periods, meaning that a reduction in resting bouts could have serious implications for nursing behaviour .…”

Cetacean mother-calf behavior observed from a small aircraft off Southern California

“…Human-related activities involving underwater noise in the marine environment (e.g., seismic airguns, oil drilling, naval sonar, vessel traffic, pile driving, tourism) under some circumstances and received sound levels disturb and interrupt feeding, socializing, resting and diving patterns of cetaceans (e.g., Lundquist, Gemmell, & Würsig, 2012;Melcón et al, 2012;Richardson et al, 1995;Southall et al, 2007), including mother and calf humpback whales (Lebrón, 2012;Morete et al, 2007). Anthropogenic disturbance of nursing by cetacean calves has not been demonstrated.…”

Effects of boats on the surface and acoustic behaviour of an endangered population of bottlenose dolphins

“…Calves (<1 yr old) were defined as individuals <1/2 the length of an adult, with visible foetal fold marks, and swimming in close association with a female. Behaviour state was defined as the predominant activity of > 50% of the group (Lusseau 2003a, Williams et al 2006, Lundquist et al 2012). This was determined by scan sampling (Altmann 1974) and characterised as 1 of 6 states: travelling, milling, resting, diving, socialising, or actively interacting with boats (Table 2).…”