Karen A. Stockin

Factors Affecting the Occurrence and Demographics of Common Dolphins (Delphinus sp.) in the Hauraki Gulf, New Zealand

The common dolphin (Delphinus sp.) is the most frequently observed cetacean species in the Hauraki Gulf, a large shallow body of water on the northeastern coastline of North Island, New Zealand. Herein, we present the first data relating to the occurrence and distribution of common dolphins in this region and assess the possible effects of abiotic parameters on the demographics of this population. The presence of associated marine species is quantified, and differences in the occurrence and demographics of single and multi-species groups are examined. Sightings data were collected between February 2002 and January 2005 during boat-based surveys. We recorded 719 independent encounters with common dolphins, involving 1 to > 300 animals. Dolphin presence was significantly affected by month, latitude and depth. Group size varied significantly by month, season, depth, sea surface temperature (SST) and latitude, and was highly skewed towards smaller groups made up of < 50 animals. Larger aggregations were most frequent during the austral winter when nutrient upwelling typically leads to increased prey availability within the region. Over 70% of groups encountered contained immature animals and 25% of groups included neonates. Calves were observed throughout the year but were most prevalent in the austral summer months of December and January. Month, season, depth, and SST significantly affected group composition. Common dolphins were observed in association with four cetacean and eight avian species, most frequently with the Australasian gannet (Morus serrator) and the Bryde’s whale (Balaenoptera brydei). The distribution of dolphin-only groups differed significantly from that of dolphin-whale groups, with mono-specific groups found on average in waters that were 3.6 m shallower and 3.1oC warmer. The year-round occurrence and social organisation of common dolphins in Hauraki Gulf waters suggest this region is important both as a calving and nursery ground.

Bottlenose dolphins around Aberdeen harbour, north-east Scotland: a short study of habitat utilization and the potential effects of boat traffic

The aim of this study was to investigate the factors that affect the patterns of occurrence and habitat utilization of bottlenose dolphins around Aberdeen harbour, on the north-east coast of Scotland (UK), and their responses to boat traffic. Land-based surveys were conducted over a period of nine weeks, between early May and late July, 2002. During this time 83 sightings of bottlenose dolphins were recorded. Dolphins occurred more frecluently around midday and early afternoon, while their abundance was greater around high tide and late afternoon. Foraging was the most commonly observed activity. Dolphins were usually concentrated around the entrance of Aberdeen harbour. Their responses to boats varied considerably according to boat size, activity and speed, but there is evidence of habituation to boat traffic.

Influences of past climatic changes on historical population structure and demography of a cosmopolitan marine predator, the common dolphin (genus Delphinus)

Climatic oscillations during the Pleistocene have greatly influenced the distribution and connectivity of many organisms, leading to extinctions but also generating biodiversity. While the effects of such changes have been extensively studied in the terrestrial environment, studies focusing on the marine realm are still scarce. Here we used sequence data from one mitochondrial and five nuclear loci to assess the potential influence of Pleistocene climatic changes on the phylogeography and demographic history of a cosmopolitan marine predator, the common dolphin (genus Delphinus). Population samples representing the three major morphotypes of Delphinus were obtained from 10 oceanic regions. Our results suggest that short‐beaked common dolphins are likely to have originated in the eastern Indo‐Pacific Ocean during the Pleistocene and expanded into the Atlantic Ocean through the Indian Ocean. On the other hand, long‐beaked common dolphins appear to have evolved more recently and independently in several oceans. Our results also suggest that short‐beaked common dolphins had recurrent demographic expansions concomitant with changes in sea surface temperature during the Pleistocene and its associated increases in resource availability, which differed between the North Atlantic and Pacific Ocean basins. By proposing how past environmental changes had an effect on the demography and speciation of a widely distributed marine mammal, we highlight the impacts that climate change may have on the distribution and abundance of marine predators and its ecological consequences for marine ecosystems.

Spatial and temporal trends in the distribution of harbour porpoises, white-beaked dolphins and minke whales off Aberdeenshire (UK), north-western North Sea

Most North Sea cetacean species are wide-ranging and consequently poorly studied. Spatial and temporal trends in the distribution of the harbour porpoise Phocoena phocoena, white-beaked dolphin Lagenorhynchus albirostris, and minke whale Balaenoptera acutorostrata were assessed at a coastal North Sea study area in Aberdeenshire, Scotland. Between March 1999 and October 2001, cetacean data were collected using both land- and vesselbased survey methods. A total of 174 sightings of these three cetacean species was recorded during approximately 330 h of combined survey effort (228 h land-based and 102 h vessel-based). Harbour porpoises were present throughout the year with peak occurrence during August and September. The presence of white-beaked dolphins and minke whales was strictly seasonal, with a peak in occurrence during August. The fine-scale distribution of all three species varied within the study area, with an apparent preference for sections of coast adjacent to deeper water. Most porpoise calves and juveniles were recorded between June and September, when 35% of harbour porpoise groups contained immature animals. The proportion of calves amongst porpoise sightings was higher during June than any other month. White-beaked dolphin calves were present in 32% of groups, and occurred in all three months that the species was recorded. Group size was higher in white-beaked dolphin pods containing immature animals. The strong seasonality in occurrence of all three species may relate to requirements for breeding habitat, movements of shared prey species and/or inter-specific competition with other species.

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

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.

Seasonal occurrence and distribution of Bryde's whales in the Hauraki Gulf, New Zealand

The Hauraki Gulf is a large, shallow embayment located north of Auckland City (36°51′S, 174°46′E), New Zealand. Brydes whales (Balaenoptera edeni) are the most frequently observed balaenopterid in these waters. To assess the use of the Hauraki Gulf for this species, we examined the occurrence and distribution in relation to environmental parameters. Data were collected from a platform of opportunity during 674 daily surveys between March 2003 and February 2006. A total of 760 observations of Brydes whales were recorded throughout the study period during 371 surveys. The number of Brydes whales sighted/day was highest in winter, coinciding with the coolest median sea-surface temperature (14.6°C). Brydes whales were recorded throughout the Hauraki Gulf in water depths ranging from 12.1–59.8 m (mean = 42.3, SD = 5.1). Cow–calf pairs were most frequently observed during the austral autumn in water depths of 29.9–53.9 m (mean = 40.8, SD = 5.2). Data from this study suggest Brydes whales in the Hauraki Gulf exhibit a mix of both “inshore” and “offshore” characteristics from the Brydes whales examined off the coast of South Africa.

Bottlenose Dolphin ( Tursiops truncatus ) Abundance, Site Fidelity, and Group Dynamics in the Marlborough Sounds, New Zealand

Bottlenose dolphins (Tursiops truncatus) are consistently observed in the Marlborough Sounds, New Zealand. However, prior to the present study, no research has previously focused on this species within these waters, despite the potential for human impacts. Photo-identification undertaken during boat-based surveys conducted between 2003 and 2005 were used to assess occurrence, abundance, and movement patterns of bottlenose dolphins in the Marlborough Sounds. Longterm site fidelity was evident, with the majority of individuals resighted over multiple years. Lagged identification rates showed consistency over a 4-y period, with some individuals remaining for longer periods, while others frequently interchanged between different areas of the Marlborough Sounds. Migration rates were high, with approximately 25% leaving and entering the 890 km2 region annually. Bottlenose dolphins in the Marlborough Sounds appear to form part of a larger, open, coastal population consisting of 385 individuals, with 211 (95% CI = 195 to 232) dolphins utilizing the region per annum. While their occurrence within these waters is frequent, the Marlborough Sounds appear to be only a section of a much larger home range for this bottlenose dolphin population.

Stomach contents of common dolphin (Deiphinus sp.) from New Zealand waters

Abstract This paper provides the first report of stomach contents of common dolphin (Deiphinus sp.) from New Zealand waters. We examined 53 stomachs from 42 stranded and 11 by‐caught common dolphin from the North Island of New Zealand between 1997 and 2006. Although the diet of by‐caught and stranded common dolphin comprised a diverse range of fish and cephalopod species, the prevalent prey were arrow squid Nototodarus spp., jack mackerel Trachurus spp., and anchovy Engraulis australis. Stranded dolphins that originated from coastal waters, and dolphins by‐caught within neritic waters, fed on both neritic and oceanic prey. Moreover, this mixed prey composition was evident in the diet of common dolphin by‐caught in oceanic waters, suggesting inshore/offshore movements of common dolphin on a diel basis.

Anomalously Pigmented Common Dolphins ( Delphinus sp.) off Northern New Zealand

Anomalous pigmentations have been recorded in many cetacean species. However, typically only one variation is reported from a population at a time (e.g., an albino). Here we record a spectrum of pigmentation from common dolphins (Delphinus sp.) off northern New Zealand. Allblack, dark-morph, pale-morph, and all-white individuals, as well as variations between these have been recorded. Pale-coloured pectoral flippers are prevalent, and a number of individuals with white “helmets” have been observed.

Examining the importance of Aberdeenshire (UK) coastal waters for North Sea bottlenose dolphins (Tursiops truncatus)

Using land- and vessel-based surveys, data on the relative abundance, distribution and habitat use of bottlenose dolphins (Tursiops truncatus) in Aberdeenshire waters were collected between 1999 and 2001. Bottlenose dolphins were present throughout the year, with peak abundance during the months of March to May. The occurrence of calves was seasonal, with the proportion of calves highest during the spring months. Foraging behaviour was recorded mainly in the vicinity of Aberdeen harbour. Dolphins photographed in Aberdeenshire waters were successfully matched and con¢rmed as Moray Firth animals. The results of the present study suggest that Moray Firth bottlenose dolphins utilize Aberdeenshire waters more frequently than previously reported. Aberdeen harbour is apparently an important feeding area, and Aberdeenshire waters are regularly used by mother^ calf pairs. This has important management implications since this area of coastline does not currently form part of the designated Special Area of Conservation (SAC) for this population.