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Item Foraging ecology of common dolphins (Delphinus sp.) in the Hauraki Gulf, New Zealand : a thesis presented in fulfilment of the requirements for the degree of Master of Science (Zoology), Massey University, Albany, New Zealand(Massey University, 2006) Burgess, Elizabeth AThis study investigated the foraging ecology of common dolphins (Delphinus sp.) in the Hauraki Gulf Marine Park, off the east coast of Auckland. New Zealand. Like most species of small cetacea in the Southern Hemisphere, its foraging habits are poorly described. A total of 59 focal group follows of common dolphins were conducted between January and April 2006. Observations were conducted at the surface, recording the predominant behavioural state of the group, foraging phase, foraging strategy, group dispersion, group formation, swimming style, group heading, calf presence and associated species. All occurrences of fission-fusion events and surface behaviours were recorded. This study tested the hypothesis that foraging behaviour of common dolphins would be influenced by environmental and physical parameters, group size, calf presence and associations with other species. In the Hauraki Gulf, foraging behaviour was recorded during all common dolphin follows, with 14% ± 1.7 (mean ± s.e.) of time spent feeding. Larger groups of dolphins spent more time foraging than smaller groups. Herding accounted for a large part of the foraging behaviour of common dolphins (mean ± s.e. = 28% ± 2.3. n = 54). Larger groups were found to spend significantly more time herding than smaller groups. Herding was generally directed towards the nearest landmass. Common dolphins use a variety of foraging strategies, both individual and group coordinated strategies. High-speed pursuits (n = 29) and kerplunkmg (n= 15) were the only individual foraging strategies recorded. Coordinated feeding strategies employed were synchronous diving (n = 50), Ime-abreast (n = 28), carouselling (n = 26) and wall-formation (n = 4). Synchronous diving and carouselling were the most enduring strategies, accounting for a significant proportion of foraging behaviour (mean ± s.e. - 32% ± 0.05 and 24% ± 0.08 of instantaneous samples, respectively). Foraging strategies were typified by vanous group formations, dispersion between group members, swimming styles and breathing intervals. Foraging strategies were also observed to have different roles in dolphin foraging. Line-abreast and wall- formation were associated with herding. However, high-speed pursuit, kerplunking and carouselling were strategies synonymous with feeding. Foraging strategies were shown to be dynamic, with dolphin groups changing strategies within a foraging bout (mean ± s.e. = 3 ± 0.4). Larger groups spent more time engaged in coordinated foraging strategies than smaller groups. Noisy surface behaviours and fission-fusion events were frequently seen in synchrony with foraging behaviour. Calves present in a foraging group, typically assumed a central position in the group during herding, but remained on the periphery during feeding. When feeding, common dolphins frequently were associated with Australasian gannets (Morus senator), shearwaters (Puffinus spp.) and Bryde's whales (Balaenoptera brydei) Observations on the predatory behaviour of each species suggested a temporary close association between birds, whales and dolphins. This study showed an association of Australasian gannet flocks (n =46) and Bryde's whales (n = 27) with common dolphins, and described the nature of the joint aggregations of mixed-species feeding in the Hauraki Gulf. The behaviour of gannots and whales strongly coincided with that of the foraging dolphin group. Whales were recorded tracking behind foraging dolphins for up to one and a half hours (mean ± s.e. = 23 min ± 2.3). Observations suggest that the relationship between gannets and whales with common dolphins was deliberate, and that these species take advantage of the superior ability of dolphins to locate and concentrate prey. The associations with gannets and whales had a significant impact on common dolphin foraging behaviour. Duration of the phenomenon was predicted to be a direct function of the quantity of prey fish available. The presence of a whale had a sizable impact on the diffusion of feeding aggregations. Results from this study indicate that the benefits of coordinated team hunts implemented by common dolphins in the Hauraki Gulf are a key factor in their foraging ecology. Their cooperative foraging skills appear to not only benefit the common dolphin individual, but other species as well. Ultimately, their role as a social hunter and an abundant, apex predator in the ocean, suggests that the common dolphin is a strongly interacting species which may facilitate population viability of other species in the Hauraki Gulf ecosystem.Item Female reproductive strategies and mother-calf relationships of common dolphins (Delphinus delphis) in the Hauraki Gulf, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Albany, New Zealand(Massey University, 2004) Schaffar-Delaney, AlineThis study reviewed the habitat use, social organisation and behaviour of common dolphin groups categorised by their youngest member, as well as the behaviour of common dolphin calves of different age classes. Most newborn calves were sighted over late spring and early summer, and in water temperatures warmer than for other groups. The water depths at which common dolphin groups were found did not vary according to the age class of their youngest member. However, only groups containing newborns or infants were sighted under 20 metres of water depth. A high percentage of groups encountered contained calves (82.5%). suggesting the importance of the Hauraki Gulf for common dolphins' reproduction. Groups of common dolphins containing calves were found to be of larger size than any other group type. All groups proved to be similarly involved in different behavioural states and showed comparable patterns of association with other species, although groups including newborns were significantly less likely to be seen associated with whales and birds. Groups of common dolphins as a whole did not show a differential reaction to the boat according to the age class of their youngest member. However, mothers and their young calves kept greater distances to the boat than mothers and older calves did. suggesting that the boat may be perceived as a threat during the newborn period. Most of the behaviours that characterise mother-calf relationships varied according to calf age class. The occurrence, frequency, duration and distance of separations increased with older aged calves. A similar increase was found in the time spent without the mother, in the occurrence of association with non-mother dolphins, in the time spent in 'echelon position', and in both mothers' and calves' dive time. Mothers also had longer dive times than calves. Older aged calves tend to present the lowest proportion of synchronous breaths. These changes are likely to represent a gradual increase in calves' independence. Results from this study have extended our knowledge of common dolphins' reproductive ecology, demonstrated that studies of mother-calf relationships in pelagic species of dolphins can he achieved, and allowed future research needs to he identified and management recommendations to be made.Item Marine mammal tourism in the Bay of Plenty, New Zealand : effects, implications and management : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Marine Ecology at Massey University, Albany, New Zealand(Massey University, 2015) Meissner, Anna MWorldwide expansion of marine mammal tourism over recent decades has raised international concerns in terms of the effects of these tourism practices on the species they target. Moreover, the growth and success of the industry have often outpaced conservation planning, including in New Zealand. To illustrate, tour vessels have been operating for ca. 25 years in the Bay of Plenty (BOP), situated on the east coast of North Island, New Zealand. By 2010, a total of eight permits had been granted across the region. However, development of this local industry occurred without any baseline data on species occurrence, distribution, habitat use or behaviour. This study sought to assess the historical occurrence of the marine mammal species off the BOP and determine their spatial and temporal distribution. Current distribution, density and group dynamics were examined for common dolphins (Delphinus sp.) and New Zealand fur seals (Arctocephalus forsteri), the two most frequently encountered species in the BOP and therefore, the primarily targeted species by tour operators. The extent of anthropogenic interactions with common dolphins was investigated and their effects on dolphin behaviour examined. The number of common dolphin individuals closely interacting with tour vessels was estimated and dolphin-vessel interactions were quantified to assess repetitive encounters. In the absence of previously undertaken systematic dedicated surveys, the present study investigated the historical spatial and temporal occurrence of dolphins, whales and pinnipeds in the BOP region. The examination of opportunistic data, collected between December 2000 and November 2010 via various platforms of opportunity including but not limited to tour vessels, identified fourteen species of dolphins, whales and pinnipeds occurring in the region. Confidence criteria in successful species identification were assigned based on observer expertise, diagnostic features of reported species and percentage of records reported by observer type. Common dolphins were the most frequently encountered species, followed by killer whales (Orcinus orca), bottlenose dolphins (Tursiops truncatus) and New Zealand fur seals, other species being infrequently encountered. A detailed examination of common dolphin habitat use revealed discrepancies with previous findings (e.g. higher use of shallower waters), possibly explained by inherent biases to the opportunistic dataset. Dedicated surveys, conducted between November 2010 and May 2013, investigated the current distribution, density and habitat use of common dolphins and New Zealand fur seals. Both species exhibited a strong seasonality with contrasting occurrence in summer and autumn for common dolphins and in winter and spring for fur seals. Dolphin seasonality is suggested to be linked to movements into deeper offshore waters and/or potentially to neighbouring regions (i.e. the Hauraki Gulf) and most likely related to foraging opportunities. Fur seal seasonality suggests that the western BOP supports a non-breeding colony and that foraging reasons may explain the species occurrence in the region. Higher density of common dolphins and fur seals identified over the shelf break and reefs can be explained by enhanced productivity. First application of Markov chain analyses to common dolphin within oceanic waters, allowed examination of the effects of tourism activities on common dolphins in the BOP. Dolphin foraging behaviour was significantly affected, as dolphins spent less time foraging during interactions with tour vessels and took longer to return to foraging once disrupted by vessel presence. Disruption to feeding may be particularly detrimental to common dolphins in the BOP open oceanic habitat, where prey resources are typically widely dispersed and unpredictable. While the overall level of tour operator compliance with regulations in the bay was relatively high, non-compliance was recorded with regards to swimming with calves and extended time interacting with dolphins. Evidence of repetitive interactions between tour vessels and common dolphins were examined using photo-identification to assess potential cumulative impacts. An estimated minimum of 1,278 common dolphin individuals were identified in the region, for which the majority (86.9%) showed low levels of site fidelity (i.e. only one encounter). At least 61.7% of identified dolphins were exposed to tour vessel interactions. However, spatial (i.e. between the western and eastern sub-regions) and temporal (i.e. daily, seasonal and annual) cumulative exposure to tourism activities was observed for less than 10% of these individuals. This is likely explained by tour operators “handing over” groups or returning to areas preferentially frequented by dolphins (i.e. presumed foraging hotspots). Due to the opportunistic methods used for photo-identification, these results are indicative only of the absolute minimum of repeated interactions common dolphins may face in the region. The present thesis represents the first comprehensive assessment of marine mammal tourism in the BOP. It offers important contributions to research and conservation in this area via the critical assessment of historical occurrence of marine mammals in the region. This thesis also provides comprehensive and detailed insights into common dolphin and New Zealand fur seal temporal and spatial distribution in the area. This can serve management agencies to implement efficient conservation plans. While identifying that tourism operations significantly affect common dolphin behaviour and repetitive interactions result in cumulative exposure, this thesis supports adaptive management and further long-term monitoring of marine mammal species in general, and in the BOP region more specifically.Item Spatial ecology and conservation of cetaceans using the Hauraki Gulf, New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Marine Ecology at Massey University, Albany, New Zealand(Massey University, 2014) Dwyer, Sarah L.Understanding species’ distributions and habitat use, and how they change spatially and temporally, is crucial for conservation management. The Hauraki Gulf, North Island, New Zealand is a highly productive marine ecosystem that is important for a range of marine megafauna, including cetaceans. This study investigated the spatial and temporal distribution and habitat use of three focal species: common dolphin (Delphinus sp.), Bryde’s whale (Balaenoptera edeni) and bottlenose dolphin (Tursiops truncatus) in the Hauraki Gulf, with the overarching goal of providing scientific information for conservation and management. A dedicated research vessel was used for data collection and surveys were focused in the inner Hauraki Gulf (IHG) and off the west coast of Great Barrier Island (GBI; outer Hauraki Gulf). The likely spatial use of the Hauraki Gulf by cetaceans, and how that likelihood changes seasonally, was investigated using species distribution modelling (SDM). A novel approach to SDM for cetaceans that incorporates detection probability was investigated with occupancy models and compared with generalised linear model (GLM) outputs. Additionally, photo-identification was used to assess the population ecology of bottlenose dolphins using GBI waters for the first time in light of the reported decline in abundance in what has formerly been recognised as the core region (i.e. Bay of Islands) for the North Island population. Survey effort totalled 20,803 km in IHG and GBI waters during 279 survey days between January 2010 and November 2012. Central northern IHG regions were important for common dolphins year-round, with increased probabilities of encounter during winter and spring compared with summer and autumn at GBI. The inshore movement of common dolphins in Hauraki Gulf waters during winter may represent an overall offshore to inshore shift in distribution, combined with an influx of dolphins into the Gulf from the wider surrounding areas of the northeast coast. This is likely to be related to prey distribution. Estimates of the functional habitat models suggested that the use of more southerly waters in the IHG during summer and autumn reflects habitat use by nursery rather than by feeding dolphin groups. However, the overall predictive maps were more temporally and spatially similar to the feeding than the nursery group predictions, indicating that prey availability likely has important implications for the general distribution and habitat use patterns of common dolphins in the Hauraki Gulf. Furthermore, occupancy model outputs showed similar spatial and temporal trends in distribution and habitat use of common dolphins in the IHG as the GLMs. While incorporating detection probability reduced the bias in parameter estimates, the depth covariate was still identified as the most important predictor of seasonal occurrence using both model types. Overall, the spatial and temporal distribution patterns of Bryde’s whales were the most unpredictable of the focal species, particularly inter-annually off GBI. Notably, habitat use by Bryde’s whales and common dolphins in GBI waters was considerably different, unlike in IHG waters. This may be indicative of whales foraging more frequently on krill in outer Hauraki Gulf waters than in the IHG, albeit dependent on inter-annual variation in prey availability. It is important to note that the results of this study occurred under predominantly La Niña conditions. Given the strong effects of winds on ocean circulation in the Hauraki Gulf, variations in patterns described here may vary under more neutral and El Niño conditions. The high encounter rates of bottlenose dolphins at GBI compared with the IHG support the hypothesis that GBI is a hotspot for the North Island population. Groups using GBI waters were larger than previously reported for the North Island population and predominantly contained neonates and calves. In particular, the southwest coast of GBI appeared important for bottlenose dolphins, possibly due to a combination of factors including food availability, its suitability for breeding or calving, and the likely decreased levels of anthropogenic pressures associated with other regions of the population’s home range. Photo-identification analyses confirmed overall site fidelity (MSR = 0.33) to the GBI region was high, albeit with variable re-sighting patterns among individuals. A total of 171 dolphins (CI = 162–180) used the area during the study period, representative of a significant proportion of the North Island population. Seasonal abundance estimates peaked in summer and autumn and were lower during winter months, with individuals leaving the study area for multiple seasons but subsequently returning. Thus, individuals of the North Island population clearly spend extended periods of time outside of what has formerly been recognised as their core home range. It is apparent that the GBI region is not simply being used as a corridor to reach other destinations but instead is a key location for at least a part of the North Island population. A number of important baselines have been identified via this study and the future challenge will lie in securing enough resources to ensure continuity in research and monitoring for further conservation purposes. The fact that the use of GBI waters by bottlenose dolphins has been overlooked until now highlights the need for researchers, managers and funding agencies to maintain an open outlook on their population of interest as a whole when conducting or funding research. For management of North Island bottlenose dolphins to be effective, a comprehensive approach including the entire home range of this population along the northeast coast is required. This research also demonstrated for the first time that occupancy models can be successfully applied to cetacean sighting data to assess habitat use while simultaneously accounting for imperfect detection. There was strong agreement between predicted areas of high use for common dolphins identified by the GLMs and occupancy models. This congruency between different model types suggests that the predictive maps presented here provide reliable seasonal distributional information that will be useful to support current and future conservation initiatives. An improved understanding of the processes driving the differences in habitat use will enable refined predictions of spatial and temporal distribution, which is required for effective management and conservation of cetaceans using the Hauraki Gulf.Item The behaviour and ecology of short-beaked common dolphins (Delphinus delphis) along the east coast of Coromandel Peninsula, North Island, New Zealand : with a note on their interactions with humans : a dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Science at Massey University(Massey University, 2001) Neumann, Dirk R.This thesis provides new insights into the behavioural ecology of free-ranging short-beaked common dolphins (Delphinus delphis), in New Zealand. A preliminary assessment of common dolphin-human interactions was also carried out as part of this 3-yr field study (1998-2001). 166 surveys were conducted in the greater Mercury Bay area, on the east coast of Coromandel Peninsula, North Island, New Zealand. These led to 105 focal group follows, with a total of 118.2 h spent following common dolphins. Seasonal movements of common dolphins were uncovered, and are apparently tied to fluctuations in sea surface temperature. Common dolphins appear to live in a fission-fusion society. Groups frequently merged and split again. The merging of groups was often accompanied by either sexual, or feeding activity. 408 individual dolphins were identified from photographs of their dorsal fins. No evidence of long-term associations between individuals was found. Resightings of identifiable dolphins indicate movement of individuals between Mercury Bay and the Hauraki Gulf, as well as between Mercury Bay and Whakatane. This study provides the first activity budget for common dolphins in the wild. Common dolphins spent 55.6% of their time traveling, 20.4% milling, 16.2% feeding, 7.1% socialising, and 0.7% resting. This proportion did not change significantly by season, or from year to year. Common dolphins were found to feed on at least six different fish species. A number of different feeding strategies were employed to capture these fish. Some of these techniques had previously been observed in bottlenose dolphins and orca, but have never before been described for common dolphins. The results of this study suggest that common dolphins can potentially be negatively affected by interactions with humans. Boat traffic appears to disturb some dolphin groups, especially those containing few individuals. However, commercial tourism appeared to have little impact on the dolphins, at this study site. Few attempts at swimming with common dolphins resulted in a sustained interaction, but unsuccessful attempts did not elicit an obvious negative response. Fishing poses the greatest threat of physical injury and possible mortality to common dolphins. Several key issues were identified, and their value in managing human-dolphin interactions is discussed.Item Skull morphometry of the common dolphin, Delphinus sp., from New Zealand waters : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Auckland, New Zealand(Massey University, 2012) Jordan, Friederike F. J.The short-beaked, Delphinus delphis, and long-beaked, D. capensis, common dolphin, two morphotypes of the Delphinus genus, are recognized as different species. However, to date, species status of the New Zealand common dolphin, among other geographic populations, remains unclear, owing to morphometric and genetic uncertainty. This lack of taxonomic knowledge is one of the reasons preventing adequate threat status assessment. The main objective of the current skull morphometric study, the first to solely focus on New Zealand Delphinus sp., was therefore, to obtain further information regarding taxonomy and life history for conservation purposes. In particular, the study aimed (1) to determine age at cranial maturity through the computation of a suture index; and (2) to assess the validity of several cranial parameters as cranial maturity indicators through the determination of a misclassification index. Furthermore, (3) presence of cranial sexual dimorphism was investigated in (i) metric characters through ANOVA and ANCOVA analyses and in (ii) non-metric characters through Chi-Square tests. (4) The taxonomic status was assessed based on the rostrum length to zygomatic width (RL/ZW) ratio, tooth counts, and the Kalya Index. Moreover, (5) Potential regional differences between Hauraki Gulf (HG) and non-HG specimens were investigated through MANOVA analyses (metric characters), Chi-Square tests, and the computation of the mean measure of divergence (non-metric characters). In addition, (6) measurement error of two metric data acquisition methods (callipers versus microscribe) was compared through the computation of three precision estimates (variance, mean absolute difference (MAD), and relative error magnitude (REM)). A total of 67 common dolphin skulls from stranded and by-caught individuals were available for analyses. The majority of skeletal material (73.1%, n = 49), had been archived frozen as intact heads following necropsies at Massey University. Those heads were prepared as part of the present study via applying the manure decomposition method. The remaining 26.9% (n = 18) of skulls were cleaned specimens housed at the Museum of New Zealand Te Papa Tongarewa. Sex was known for 88.1% (n = 59) of specimens (males: 40.7%, n= 24; females: 59.3%, n = 35). Based on age data and the suture index, 46.3% (n = 31) and 53.7% (n = 36) of specimens were regarded as cranially immature and mature, respectively. Sex ratio of immatures was approximately 1:1 (males: n = 16, females: n = 13), while that of mature specimens was almost 1:3 (males: n = 8, females: n = 22). The suture index suggested that New Zealand Delphinus sp. obtain cranial maturity at approximately 11 years. Specimens with ≤ 6.8 % of partly worn teeth were between 1 to 3 years and cranially immature, while specimens with any number of rostral teeth worn down to the gum line were physically mature. Sexual size dimorphism, with larger sizes recorded for males, were detected in total body length (TBL) and in 22.7% (n = 15) of cranial characters analyzed, of which 86.7% (n = 13) were width measurements. In total 70.0% (n = 7) of size dimorphic characters that could be allocated to a cranial functional complex were related to the feeding apparatus. RL/ZW ratio (mean: 1.49 ± 0.06 (SD); range: 1.39 - 1.61) and upper tooth counts (45 - 56) of cranially mature New Zealand specimens assessed (pooled for both sexes) overlapped with values published for both the short-beaked and long-beaked form. Values of TBL, condylobasal length (CBL), rostrum length (RL), and zygomatic width (ZW) were also of intermediate status in both sexes. Findings reported herein suggest that New Zealand Delphinus sp. should be regarded as a large form of D. delphis until further morphometric and genetic data becomes available. No evidence of regional differences between HG and non-HG specimens was detected in either metric or non-metric characters, however, sample sizes were small. Variance of repeated measures was lower in the calliper (range: 0.1 to 0.7%) than in the microscribe (range: 1.1 to 10.7%) data set for all characters assessed (n = 33). High precision between both data sets was detected for 69.7% (n = 23) of characters (MAD below the 1 mm threshold) and REM of 93.9% (n = 31) of character was deemed excellent or good, indicating high compliance between both methods for the majority of characters assessed.Item The New Zealand common dolphin (Delphinus sp.) : identity, ecology and conservation : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology, Massey University, Auckland, New Zealand(Massey University, 2008) Stockin, Karen A.Common dolphins (genus Delphinus) are poorly understood within New Zealand waters. Prior to this study, most information relating to the taxonomy, population structure, diet and pollutant loads of this genus relied upon untested assumptions. Furthermore, factors affecting the occurrence, demographics and habitat use of common dolphins in the Hauraki Gulf remained unknown. This lack of empirical data has resulted in the inadequate recognition and management of New Zealand Delphinus. Inappropriately classified by the New Zealand Threat Classification System, the anthropogenic impacts that affect this genus have clearly been overlooked. The present study examines behaviour of common dolphins in the Hauraki Gulf and details analyses undertaken on tissue samples collected from around New Zealand. Results detailed here challenge many of the untested assumptions about this genus within New Zealand waters. The taxonomy of New Zealand common dolphins was assessed using 92 samples analysed for 577 base pairs (bps) of the mtDNA control region (D-loop). New Zealand samples were compared with 177 published sequences from eight other populations from around the world. New Zealand Delphinus exhibited a high genetic variability, sharing haplotypes with both short- (D. delphis) and long-beaked (D. capensis) populations. Indeed, the New Zealand population showed significant genetic differentiation when compared with most other populations world-wide. Furthermore, intrapopulation analyses revealed significant genetic differentiation between Hauraki Gulf individuals and other common dolphins sampled within New Zealand waters. Results suggest habitat choice and site fidelity may play a role in shaping the fragmented population structure of New Zealand Delphinus. Data relating to the occurrence and demographics of common dolphins in the Hauraki Gulf region were collected during boat-based surveys between February 2002 and January 2005. In total, 719 independent encounters, involving one to > 300 common dolphins were recorded. 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 comprising fewer than 50 animals. Calves were observed throughout the year but were most prevalent in the austral summer months of December and January. Group composition was significantly affected by month, season, depth and SST. The yearround occurrence and social organisation of Delphinus in Hauraki Gulf waters suggest this region is an important nursery and potential calving area. The effects of diel, season, depth, sea surface temperature, and group size and composition on dolphin behaviour were investigated using activity budgets. Foraging and social were the most and least frequently observed behaviours, respectively. A correlation between group size and behaviour was evident, although behaviour did not vary with the composition of dolphin groups. Resting, milling and socialising animals were more frequently observed in smaller groups. Foraging behaviour was prevalent in both small and large groups, suggesting foraging plasticity exists within this population. Behaviour differed between single- and multi-species groups, with foraging more frequent in mixed-species aggregations, indicating the primary mechanism for association is likely prey-related. Stomach contents analysed for forty-two stranded and eleven commercially by-caught individuals collected from around North Island, New Zealand between 1997 and 2006, revealed arrow squid (Nototodarus spp.), jack mackerel (Trachurus spp.) and anchovy (Engraulis australis) as the most prevalent prey. Stranded individuals and dolphins bycaught within neritic waters fed on both neritic and oceanic prey. Moreover, a mixed prey composition was evident in the diet of common dolphins by-caught in oceanic waters, suggesting inshore/offshore movements of New Zealand Delphinus on a diel basis. Additionally, prey differences were also evident in the stomach contents of common dolphins sampled from within the Hauraki Gulf. Trace elements, polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticide levels were determined in five stranded and fourteen by-caught Delphinus sampled from around New Zealand between 1999 and 2005. Generally, levels of trace elements were low. However, concentrations of OC pesticides were similar in range to those previously reported for Hector’s (Cephalorhyncus hectori) and common bottlenose dolphins (Tursiops truncatus). Organochlorine pesticides dieldrin, hexachlorobenzene (HCB), o,p’-DDT and p,p’-DDE were present at the highest concentrations. Markov chain models were used to assess the impact of tourism activities on Delphinus within the Hauraki Gulf. Foraging and resting bouts were significantly disrupted by boat interactions. Both the duration of bouts and the time spent in these two behavioural states decreased during boat interactions. Additionally, foraging dolphins took significantly longer to return to their initial behavioural state in the presence of a tour boat. Impacts identified are similar to those previously reported for the common bottlenose dolphin, a coastal species typically considered to be more susceptible to cumulative anthropogenic impacts. Data presented here reveal the nature and apparent susceptibility of New Zealand common dolphins to human-induced impacts, namely fisheries by-catch, pollution and tourism. This in conjunction with taxonomic uncertainty, lack of abundance estimates and the year-round use of inshore waters for feeding, clearly warrants immediate attention from managers. Furthermore, the current threat classification of New Zealand Delphinus should be reconsidered in light of population uncertainties, and in view of the susceptibly to human-induced impacts revealed by the present study.