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a b s t r a c tThis study investigated Burrunan dolphin responses to dolphin-swim tour vessels across two time periods : 1998-2000 and 2011-2013. A total of 211 dolphin sightings were documented across 306 surveys. Sighting success rate and mean encounter time with dolphins decreased significantly by 12.8% and 8.2 min, respectively, between periods. Approaches that did not contravene regulations elicited highest approach responses by dolphins towards tour vessels, whereas dolphins' responded to illegal approaches most frequently with avoidance. Small groups responded to tour vessels with avoidance significantly more than large groups. Initial dolphin behaviour had a strong effect on dolphin's responses to tour vessels, with resting groups the most likely to exhibit avoidance. Calves were significantly more likely to be present during swims in 2011-2013. Dolphin's responses to tour vessels changed across time, with effect responses (avoidance and approach) increasing significantly as dolphins gained cumulative experience. These dolphins are forced to expend a greater level of time and energy avoiding or approaching boats, shifting from a noneffect response to an effect response. Consequences of this include possible decrease in biological fitness by detracting from core biological activities such as foraging and resting. Combined with a decrease in sighting success between periods, the results imply that this population of dolphins, which is endemic to Australia and listed as threatened under the Victorian Flora and Fauna Guarantee Act 1988, may not be well suited to the dolphin-swim industry. The management implications of these results warrant a shift from passive to active management in Port Phillip Bay. The importance of long-term research is highlighted, given behavioural responses detected herein would be undetected in short-term studies.

Within Australian waters, short-beaked common dolphins (Delphinus delphis) are exposed to a variety of human-induced impacts, including aquaculture and fisheries. Nonetheless, the occurrence and distribution of common dolphins within these waters remains unknown. Data detailed herein represent the first report of the occurrence and distribution of common dolphins from Australian waters. The density and relative abundance of common dolphins within Gulf St. Vincent (GSV), South Australia, was examined between September 2005 and May 2008 using systematic boat surveys. During 1,850 km of survey effort, a total of 108 independent groups, involving 564 common dolphins, were observed. Group size ranged from 2 to 21 individuals (mean = 5.26, SD = 3.687), with immature dolphins found in larger group sizes. Adults were the most frequent age class observed in this population (60.3%, n = 340), with neonates and calves observed most frequently between December and April. Sighting frequency was 3 groups/100 km² travelled, with an encounter rate of 16 common dolphins/100 km². The western longitude and southern latitude sections of GSV were used most frequently by this species, with most groups recorded in water depths of 35 to 40 m (mean = 37.2 m, SD = 1.4), and in areas 21 to 31 km from land (mean = 27.4 km, SD = 2.6). Common dolphin density was estimated to be 0.5 dolphins/100 km 2 , with a population estimate of 1,957 dolphins within their preferred habitat (waters deeper than 14 m). Results suggest the GSV is important for this species and that common dolphins use these waters as a nursery area.