Behaviour of dwarf minke whales (Balaenoptera acutorostrata subsp.) associated with a swim-with industry in the northern Great Barrier Reef
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A diffuse aggregation of dwarf minke whales occurs in the northern Great Barrier Reef World Heritage Area during the austral winter months. This area coincides with a region heavily used by a large dive and snorkel tourism industry. Over the last two decades a small part of this industry has developed into a swim-with dwarf minke whale industry that has been limited via a permit scheme since 2003. Very little was understood about the whales' behaviour or the response of the whales to the vessels and swimmers. In order to address this knowledge gap, I designed this study with two major aims: (1) to provide detailed insights into the behaviour of dwarf minke whales around tourism vessels and swimmers, and (2) to establish recommendations for the tourism industry and management agencies to provide for discussions on future management and to contribute to the sustainability of this industry. During my research (2006-2008), I described over 30 distinctive dwarf minke behaviours and provided evidence for the presence of behaviours with potential social and investigative functions. Behaviours with likely social attributes such as belly presentations and bubble releases, were significantly influenced by a large group size (>6 animals), while investigatory behaviours such as close and very close approaches, motorboating, and headrises were positively influenced by the presence of resighted animals. Dwarf minke whales are a predominantly solitary oceanic species. When they form social groups, behaviours which convey information among conspecifics via visual communication (e.g. presenting the white belly or releasing bubbles) may be particularly important. The presence of several investigative behaviours during interactions with vessels and swimmers highlights the inquisitive nature of these whales and suggests that such behaviours are an important part of their ecology (i.e. finding mates, food or avoiding predators). I also investigated potential agonistic and disturbance displays of dwarf minke whales and provided an indication on the metabolic costs of interacting with humans. The scarcity of agonistic and disturbance responses and the absence of avoidance behaviours, all suggest that the vessels and swimmers have a relatively low impact on the whales. Nonetheless, several behaviours including close (>1-3 metres) and very close (≤ 1 metre) approaches to human observers and potential agonistic and disturbance behaviours (e.g. gapes/gulps, jaw claps) were identified as of potential harm to both the whales and the swimmers. The investigative nature of dwarf minke whales was further explored by quantifying the distribution of interacting whales around vessels and swimmers and examining if their behaviour changes in interactions with humans over time. Dwarf minke whales voluntarily approached dive tourism vessels and maintained contact for prolonged periods (X ± SE, 2006-2008 = 171 ± 11 minutes). These whales showed a highly clumped distribution around the vessel, surfacing more often within a 60 metres radius of the boat than expected and aggregating around swimmers. My results also suggest that dwarf minke whales change their behaviour over time in interactions with humans. Individual whales repeatedly passed very close to the swimmers (X=7.08 metres ± SE 0.09 metres; N=119 whales) and significantly decreased their passing distance over the course of an interaction. In both cases, closeness was significantly influenced by group size; the larger the group of whales, the closer individuals approached the observers. Individual dwarf minke whales significantly decreased their passing distance in subsequent interactions and resighted animals approached swimmers significantly closer than unknown individual whales. The voluntary initiation of contact with humans, the whales' close and prolonged association with the vessel and swimmers, the closeness of their approaches and the increased familiarity to the stimuli, all suggest a strong exploratory drive of dwarf minke whales. Indeed, the inquisitive behaviour of dwarf minke whales contrasts with the behaviour of most free-ranging marine mammals interacting with humans. These behavioural attributes raise management issues and concerns about the safety of both the whales and the human participants. I assessed the risk of harm associated with swimming with dwarf minke whales for both, the swimmers and the whales using both, my observational data and the perceptions of Key Informants (marine mammal experts, and members of management and non-governmental organisations). This assessment revealed that most dwarf minke whale behaviours displayed during interactions are of low risk of harm to the swimmers and the whales. Nevertheless, in a fifth of the total observed interactions (n=101) there was at least one whale behaviour present with potential to harm swimmers and/or whales. In addition, I identified 22 occasions from all interactions of the endorsed industry (N=467; 2006-2008) where whales made physical contact with objects (e.g. ropes, dinghy) or swimmers and five (22%) of those incidents were caused by only one individual resighted whale. The Key Informants perceived the risk of harm to swimmers from the swim with industry as much greater than the risk of harm to the whales. Nonetheless they were concerned about the wellbeing of the whales in the medium to longer term, i.e. the potential of such industries to change the behaviour of the whales and impact on their behavioural budget and fitness. Most Key Informants evaluated the current swim-with dwarf minke whale industry positively; however, they considered that this industry needs continuous monitoring and future research in order to identify any long-term impacts and to address research gaps for adequate management. I also evaluated the accuracy of data collected by crew on dwarf minke whale behaviours. The crew reported dwarf minke whale behaviours via the Whale Sighting Sheets. I compared these records (presence/absence of behaviour per encounter) with my data. The best fitting commonalities between my observations and data reported via the Whale Sighting Sheets were between close (>1-3 metres) and very close approaches (≤ 1 metre), headrises, motorboating and touching behaviour. For crew to be able to identify these particular whale behaviours is important for both, cost-efficient longer-term monitoring and the risk management of interactions. I also used a passenger questionnaire (Interaction Behaviour Diary) to evaluate passengers' satisfaction with their whale swims, and to investigate their perceptions about potential harmful dwarf minke whale behaviours. Swimmers were more satisfied when dwarf minke whales approached very close (≤ 1 metre) to them and perceived such close encounters as harmless. Both these reactions pose challenges to the effective management of risks associated with interactions. This study is the first comprehensive assessment of the behaviour of a baleen whale associated with a tourism industry. It provides a scientific basis for future studies on dwarf minke whales and will be useful for behavioural studies of other baleen whales associated with humans. This study provides specific recommendations to improve the future management of the swim-with dwarf minke whale industry and to ensure the protection of this species.
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271
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DOI
10.25903/7s4j-f788