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    Multidimensional trace metals and nutritional niche differ between sexually immature and mature common dolphins (Delphinus delphis)
    (Elsevier Ltd., 2023-06-26) Stockin KA; Machovsky-Capuska GE; Palmer EI; Amiot C
    There is a need to understand the links between metals and nutrition for apex marine predators, which may be subject to different ecotoxicological effects at different life stages. We combined stomach content analyses (SCA), prey composition analysis (PCA), the Multidimensional Niche Framework (MNNF) with Bayesian multivariate ellipses, trace metal analysis and nicheROVER to investigate nutrition and trace metals across sex, age, and sexual maturity status in common dolphins (Delphinus delphis) from New Zealand. A broader prey composition niche breadth (SEAc) was estimated for immature compared to mature conspecifics, showing a higher degree of prey and nutrient generalism driven by protein (P) intake. Cd and Zn niche similarities suggests these metals were incorporated through similar prey in both immature and mature dolphins, whereas Hg and Se niche divergence indicates uptake occurred via different prey. Our multidisciplinary assessment demonstrated how nutrients and metal interactions differ in common dolphins depending upon sexual maturity. This approach has relevance when considering how marine pollution, environmental fluctuations and climate change may affect nutritional and trace metal interactions during different reproductive stages within marine predators.
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    Spatial ecology of delphinids in Queen Charlotte Sound, New Zealand : Implications for conservation management : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Marine Ecology Massey University, Albany, New Zealand
    (Massey University, 2019) Cross, Cheryl Lynne
    Understanding species’ ecological interactions and area usage depends on clear insight into their temporal and spatial patterns. Such information combined with recognition of regional human-invested interests, is crucial for developing conservation management efforts. Queen Charlotte Sound (QCS), South Island, New Zealand is a unique environment inhabited by diverse marine life, including several cetacean species. The area is subject to rising levels of anthropogenic activity inclusive of marine farming, tourism and vessel traffic. With conservation management in mind, this thesis focused on three key delphinid species: Hector’s (Cephalorhynchus hectori), bottlenose (Tursiops truncatus) and dusky dolphins (Lagenorhynchus obscurus). Specifically, this study sought to: 1) explore long-term historical temporal and spatial trends in delphinid occurrence 2) identify recent patterns in delphinid distribution, density and range 3) investigate delphinid species’ habitat use 4) initiate research of regional swim-with-dolphin tourism. Dolphin sighting data were: 1) collated from tour vessel logbooks spanning 1995–2011 and 2) collected during dedicated surveys aboard opportunistic platforms from 2011–2014. Dynamic and static environmental variables were sourced from local government agency databases to use in analyses with both datasets. Historical delphinid presence (from logbook data) was correlated with dynamic environmental variables during two separate time frames (1995–2002; 2003–2011), using Generalized Additive Models (GAMs) and Generalized Linear Models (GLMs). Spatial patterns of these sightings were explored across temporal periods (i.e., seasons; blocks of year). Dedicated survey data were used to generate kernel density estimates and to determine species’ range and central range. These dolphin density estimates were correlated with static and dynamic habitat parameters using (GAMs). Spatial predictions were then generated from the resultant significant variables. Bottlenose dolphin engagement in swim-with-dolphin encounters was assessed according to several proxies using Linear Models (LMs) and GLMs. A total of 5,295 historical records consisting of 6,055 delphinid sightings were compiled, demonstrating a long-term presence of the focal species. Of these, Hector’s dolphins consistently had the highest trip encounter rate. Seasonal patterns indicated peaks in occurrence for Hector’s during summer/autumn, bottlenose during autumn/winter and dusky dolphins during winter/spring. Further investigation with GAMs suggested that each species’ presence was associated with a unique set or range of dynamic variables. Annual variation occurred amongst all species. During both historical time frames (1995–2002 and 2003–2011), Hector’s dolphin occurrence was associated with higher SST values. Bottlenose dolphins displayed an association with mid-low SST (during 1995–2002) and with high turbidity (during 2003–2011). Dusky dolphins were influenced by low SST (during both time frames) and from 2003–2011 were also influenced by low turbidity and mid-value tidal range. Spatial patterns illustrated that Hector’s and dusky dolphins have become more restricted in their use of QCS over time. Finally, logbook data indicated an increased prevalence of swim-with-dolphin encounters, suggesting an expansion of local tourism from 2004–2011. A total of 677 dedicated opportunistic surveys were completed. These equalled 1,613 hrs of search effort spanning 263 km2. Sighting rate calculations indicated that Hector’s and bottlenose dolphins occurred more frequently than dusky dolphins. Seasonality was particularly notable amongst Hector’s dolphins, whereas the sighting and encounter rates were higher during summer and autumn. The collective range of all species suggests that delphinids utilized most of QCS. However, both the range and central range of Hector’s dolphins were more limited. Notable spatial patterns included peaks in Hector’s dolphin density mid-Sound, during summer/autumn and peaks in bottlenose dolphin density toward the outer Sound during summer/autumn. Temporal overlap was relatively high for bottlenose and Hector’s dolphins (0.67) and low for Hector’s and dusky dolphins (0.22), while spatial overlap was quite low for all species combinations. The patterns explored here offer evidence of temporal and spatial multi-species habitat partitioning within QCS. This may be due to the broader ecological trends within New Zealand and is likely attributed to the availability and movement of prey. Habitat models (GAMs) indicated a unique set of significant drivers associated with dolphin density for each species. Hector’s dolphins displayed an association with dynamic and static variables (SST, fluorescence, depth, slope and distance to the closest marine farm). Dusky dolphins were influenced by the same variables, as well as year. Consistency with the earlier models in the association with SST for Hector’s (higher values) and dusky dolphins (lower values) was detected. Bottlenose dolphins were only influenced by static variables (depth, slope and distance to the closest marine farm) and year. The habitat differences suggested by these models offer further insight to the ecological meaning of dolphin spatial patterns in QCS. In particular, these findings offer additional evidence of delphinid resource partitioning, specifically on a trophic scale. This likely occurred because all three species exhibit both dietary and foraging plasticity. While similarities were observed between comparable studies in other areas, the presence of some variation is likely due to unique physical and hydrographic regional characteristics. Spatial predictions that were generated from significant model variables were valuable in estimating potential locations of dolphin density beyond sighting locations, including areas that they previously occupied. Data representing animal area usage, like those presented here, are integral to conservation management, especially amidst growing anthropogenic influences, like tourism. This first ever tourism-based study in QCS indicated bottlenose dolphins as the main target species for swim-with-dolphin activity. A total of 190 bottlenose dolphin swim encounters were assessed according to several proxies. Interactions were very short (𝑥̅=4.2 min), with most dolphin reactions neutral (82.9 %), suggesting animal disinterest. Swim encounters occurred regularly, irrespective of group composition or behavioural state. Furthermore, tour operators travelled great distances (𝑥̅=11.7 km) amongst dolphin groups to complete swim encounters, demonstrating pursuit of interaction. Collectively, these proxies suggest a lack of dolphin engagement in swim activity. This thesis encompassed the first multi-species comprehensive assessment of delphinid density, range, habitat use and swim-with-dolphin tourism in QCS. It established a baseline of data, contributing to regional ecological knowledge. Detailed evidence of when and where three sympatric dolphin species utilized QCS was provided. Moreover, this work established an understanding of delphinid inter-specific interactions and associations with habitat variables. Applications of the findings presented here include contributions to developing comprehensive conservation management and further research. Periods and regions of high density and predicted density may be considered in regional management decisions regarding anthropogenic use of the Sound and during the design of future surveys.
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    The occurrence and habitat use of common dolphins (Delphinus sp.) in the central Bay of Plenty, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology, Massey University, Auckland, New Zealand
    (Massey University, 2012) Gaborit-Haverkamp, Tania
    This thesis investigated the occurrence and habitat use of common dolphins (Delphinus sp.) inhabiting the central Bay of Plenty (BOP), North Island, New Zealand. Although common dolphins are the most prevalent species of dolphin found off the east coast of the North Island of New Zealand, there has been no long term empirical investigation of the species in the central BOP area. Behaviour of common dolphins in the presence of the observation platform was also assessed to investigate habitat use. Additionally, data describing other cetacean species occurring within this region are presented in order to place into context the importance of these waters for Delphinus. Sightings data were collected between March 1998 and May 2011 during 2364 boat-based surveys on board platform of opportunity, tourism vessel Gemini Galaxsea (a 60 ft ketch sailboat). Variables examined included location, group size, composition, water depth, time of day, seasonality, behaviour and the presence of associated species. Common dolphins were encountered during 54% (n = 1265) of surveys, in water depths ranging from 5.0 to 197.0 m. Delphinus sightings primarily occurred in the area between Motiti Island, Mayor Island and Waihi on the mainland. Group size ranged from one to 500+ individuals and was significantly affected by the time of day, month and depth of sightings. The most frequently recorded group size involved 50 to 100 animals, with larger aggregations more frequent during the warmer austral months when nutrient upwelling leads to increased prey availability in coastal waters off the BOP. Groups containing immature animals accounted for 16% of total sightings and occurred throughout the year, although neonate calves were only reported during the warmer austral summer months, supporting the concept of reproductive seasonality in this population. Common dolphin groups sighted within the central BOP were reported in association with five marine mammal species and 14 avian species, most frequently with various species of petrel (Procellariiformes) and the Australasian gannet (Morus serrator). The year round occurrence of common dolphins within central BOP waters indicates that this region maybe important for Delphinus. Behavioural data were collected from 162 independent dolphin groups. Overall, forage, social and travel accounted for the majority of recorded behavioural states, while mill and rest were less frequent. Behaviour was influenced by water depth, with foraging dolphins encountered in the deepest waters. Behaviour also varied significantly according to group size, with 4 foraging occurring more often than expected in large groups and resting, socialising and milling occurring more often in smaller groups. The presence of immature animals also had a significant influence on common dolphin behaviour, with foraging occurring more often than expected in groups containing immature animals. The presence of associated species varied according to behaviour, with the majority of foraging groups occurring in the presence of Australasian gannets. Seasonal and diurnal peaks in behaviour were not evident. Social behaviours primarily occurred during summer when large nursery groups were also reported in the central BOP. In order to place into context the use of central BOP waters for Delphinus, an investigation of other cetacean species using these waters was undertaken; eleven cetacean species (6 Mysticeti and 5 Delphinidae) were identified as utilising central BOP waters. Sightings primarily occurred in the area between Karewa Island, Mayor Island (Tuhua) and Motiti Island in the central BOP. The majority of delphinid sightings occurred in spring and involved the bottlenose dolphin, Tursiops truncatus (50.5%) and killer whale, Orcinus orca (42.9%). Pilot, Globicephala spp. (3.8%) and false killer whale, Pseudorca crassidens (2.9%) sightings were less frequent. Group sizes ranged from solitary to 200+ individuals. Calf presence was recorded for bottlenose dolphins during summer and autumn and killer whales during spring and autumn. Pilot and false killer whale calves were not recorded during the study period. The majority of baleen whale sightings occurred during winter and spring and involved minke, Balaenoptera acutorostrata/bonaerensis (44.3%), blue, B. musculus (19.0%) and Bryde’s whales, B. edeni (16.5%). Humpback, Megaptera novaeangliae (10.1%), sei, B. borealis (8.9%) and southern right whale, Eubalaena australis (1.3%) sightings were less frequent. Group sizes ranged from solitary to four individuals, with results highly skewed towards solitary animals (79%). Cow-calf pairs were observed during spring for all baleen whales except sei and humpback. Cetaceans were primarily observed in association with the Australasian gannet as well as various species of petrel and shearwater (Puffinus spp.). Bottlenose dolphins and false killer whales were sighted together in mixed species groups. Bryde’s whales were also sighted in association with common dolphins.
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    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.