An ecological and behavioural approach for managing boating impacts on dolphins in the dolphin-watching capital of Australia

The population of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the newly formed Port Stephens Marine Park, NSW, is the target of the largest dolphin-watching industry in Australia. I investigated (1) potential impacts of dolphin-watching boats (DWs) including aspects such as number of vessels, as well as distances from dolphin groups, (2) different experimental boat approach distances, (3) effectiveness of Speed Restriction Zones (SRZs), and (4) fine-scale habitat use of dolphins, from August 2008 to August 2010. -- (1) The presence of DWs altered both the dolphins' behavioural states and activity budgets. Dolphins spent significantly less time feeding and were never observed to rest in the presence of DWs. These effects were exacerbated as the number of boats increased and the distance from boats decreased, with feeding in particular compromised by boat number. -- (2) Analysis of experimental boat approaches showed that there was significantly less feeding and resting when boats approached them at close range. -- (3) SRZs were more intensely used than Control Zones (CZs) by DWs in summer. In contrast, dolphin groups including calves used SRZs less during summer. -- (4) Spatial modeling of habitat use showed that dolphins preferred shallow areas that are closer to shore for resting but have no preferred habitat when feeding. -- This study recommends stricter regulations than currently legislated including restricting the number of DWs to no more than one within 50 m of a dolphin group with only adults and 150 m with a group including calves to enable groups to feed. Given the critical impact of any boats on resting, the location, size, and accompanying regulations regarding SRZs have to be revised. Total Exclusion Zones should be considered to reduce pressure on dolphins undertaking critically important activities. Management plans whose stated goals include both sustainability of a dolphin-watching industry and longer-term viability of a dolphin population may reconcile conflicting objectives and improve decision-making by using these empirical measures rather than best guesses.