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Effective management of space-use conflicts with anthropogenic activities is contingent upon reliable knowledge of a species’ ecology. The Māui dolphin Cephalorhynchus hectori maui is endemic to New Zealand and is listed as Critically Endangered, mainly as a result of fisheries bycatch. Despite conservation efforts, the population was estimated at 55 animals in 2011. Here we investigate environmental correlates of Māui dolphin nearshore distribution, using 119 encounters with Māui dolphin groups during boat-based, coastal surveys across 4 summers (2010, 2011, 2013, 2015). We describe the nearshore distribution using a kernel density analysis with differential smoothing on the x- and y-axes to account for the nearshore preference of the dolphins and the survey design. In all years, dolphins were encountered consistently in a restricted area (4 year area of overlap: 87.3 km²). We modelled habitat preference with boosted regression trees, using presence/absence of dolphins relative to static and dynamic environmental predictors. An index of coastal turbidity was created based on a near-linear relationship between Secchi disk measurements and log-transformed remotely sensed chl a concentration. Sea surface temperature (SST; 22.6% contribution), turbidity (22.2%), distance to major watersheds (17%), depth (14.5%), distance to minor watersheds (13.3%) and distance to the coast (10.4%) partly explained Māui dolphin distribution. We detected a match between predicted areas of high nearshore habitat suitability around North Island and historical sightings (76.2% overlap), thus highlighting potential areas of Māui dolphin recovery. Our study presents methods broadly applicable to distribution analyses, and demonstrates an evidence-based application toward managing Māui dolphin habitat.

1. Marine protected areas (MPAs) have been advocated for the protection of threatened marine mammals, but there is no empirical evidence that they are effective. In 1988, the Banks Peninsula Marine Mammal Sanctuary was established to reduce gillnet mortalities of Hector's dolphin Cephalorhynchus hector i, an endangered dolphin species endemic to New Zealand. This study assesses the effectiveness of the MPA in improving the survival rate of Hector's dolphin at Banks Peninsula. 2. Over 21 years, we undertook photo-identification surveys of Hector's dolphins along standardized transects from small outboard-powered boats. From 1986 to 2006, we photographically captured 462 reliably marked individuals. We estimated mean annual survival during the pre-sanctuary and post-sanctuary periods by applying a Bayesian random effects capture-recapture model to the data. Population growth was estimated from population simulations using a stage-structured matrix model. 3. We estimate a 90% probability that survival has improved between the pre-sanctuary and postsanctuary periods, with estimates of mean survival probability increasing by 5-4% (from 0-863 to 0-917). This improvement in survival corresponds to a 6% increase in mean annual population growth (from 0-939 to 0-995). 4.Synthesis and applications.Our study demonstrates improvement in a demographic parameter of an endangered marine mammal species following conservation action. Our results provide evidence that area-based protection measures can be effective for marine mammals. We note that estimating demographic parameters in marine mammals requires many years of data to achieve sufficient precision to detect biologically meaningful change. MPAs should be established with a commitment to long-term monitoring.

Species distribution models (SDMs) can be used to predict distributions in novel times or space (termed transferability) and fill knowledge gaps for areas that are data poor. In conservation, this can be used to determine the extent of spatial protection required. To understand how well a model transfers spatially, it needs to be independently tested, using data from novel habitats. Here, we test the transferability of SDMs for Hector's dolphin (Cephalorhynchus hectori), a culturally important (taonga) and endangered, coastal delphinid, endemic to Aotearoa New Zealand. We collected summer distribution data from three populations from 2021 to 2023. Using Generalised Additive Models, we built presence/absence SDMs for each population and validated the predictive ability of the top models (with TSS and AUC). Then, we tested the transferability of each top model by predicting the distribution of the remaining two populations. SDMs for two populations showed useful performance within their respective areas (Banks Peninsula and Otago), but when used to predict the two areas outside the models' source data, performance declined markedly. SDMs from the third area (Timaru) performed poorly, both for prediction within the source area and when transferred spatially. When data for model building were combined from two areas, results were mixed. Model interpolation was better when presence/absence data from Otago, an area of low density, were combined with data from areas of higher density, but was otherwise poor. The overall poor transferability of SDMs suggests that habitat preferences of Hector's dolphins vary between areas. For these dolphins, population‐specific distribution data should be used for conservation planning. More generally, we demonstrate that a one model fits all approach is not always suitable. When SDMs are used to predict distribution in data‐poor areas an assessment of performance in the new habitat is required, and results should be interpreted with caution. Species distribution models (SDMs) are commonly used to predict habitat and distribution for species in data poor areas, under the assumption that habitat use is the same across space. We tested the transferability of SDMs for Hector's dolphin, revealing differences in habitat use between populations. These results indicate that to understand habitat use of Hector's dolphin, local data is required for the model building process.

Understanding genetic differentiation and speciation processes in marine species with high dispersal capabilities is challenging. The Chilean dolphin, Cephalorhynchus eutropia, is the only endemic cetacean of Chile and is found in two different coastal habitats: a northern habitat with exposed coastlines, bays and estuaries from Valparaíso (33°02'S) to Chiloé (42°00'S), and a southern habitat with highly fragmented inshore coastline, channels and fjords between Chiloé and Navarino Island (55°14'S). With the aim of evaluating the potential existence of conservation units for this species, we analyzed the genetic diversity and population structure of the Chilean dolphin along its entire range. We genotyped 21 dinucleotide microsatellites for 53 skin samples collected between 1998 and 2012 (swab: n = 8, biopsy: n = 38, entanglement n = 7). Bayesian clustering and spatial model analyses identified two genetically distinct populations corresponding to the northern and southern habitats. Genetic diversity levels were similar in the two populations (He: 0.42 v/s 0.45 for southern and northern populations, respectively), while effective size population was higher in the southern area (Ne: 101 v/s 39). Genetic differentiation between these two populations was high and significant (FST = 0.15 and RST = 0.19), indicating little or no current gene flow. Because of the absence of evident geographical barriers between the northern and southern populations, we propose that genetic differentiation may reflect ecological adaptation to the different habitat conditions and resource uses. Therefore, the two genetic populations of this endemic and Near Threatened species should be considered as different conservation units with independent management strategies.

Prediction of future population trajectories is vital in the management of threatened species but requires accurate estimates of demographic rates. One such parameter is fecundity, which is commonly expressed as the number of offspring produced per female per year. The endangered Hector's dolphin (Cephalorhynchus hectori) is Aotearoa New Zealand's only endemic cetacean and is threatened by bycatch from inshore trawl and gillnet fisheries. Here, we take advantage of 40 years of continued photo‐identification effort at Banks Peninsula to construct a Bayesian open‐population multi‐event capture–recapture model. We estimated fecundity for Hector's dolphins at 0.29 (95% credible interval [CI]: 0.22–0.39) which corresponds to an average calving frequency of one calf every 3.4 years (95% CI: 2.5–4.7 years). This new estimate is substantially lower and more precise than the previous estimate of fecundity for Hector's dolphins (e.g., 0.409, 95% CI: 0.267–0.635), but is based on a larger dataset, and aligns closely with estimates from other dolphin species. This updated estimate of fecundity indicates a lower capacity for population growth and reduced resilience to anthropogenic threats, including bycatch in fisheries. Updated estimate of fecundity for Hector's dolphin is lower and more precise than prior estimation. This latest estimate suggests a lower capacity for population growth than previously thought and a reduced resilience to anthropogenic threats.

Environmental DNA (eDNA) is frequently used for detecting species and describing biodiversity through metabarcoding techniques. More recently, there has been emerging evidence that eDNA can be used to investigate intraspecific variability, providing novel pathways to explore population genetics questions. However, it can be difficult to distinguish between true intraspecific variation and PCR/sequence error, and the presence of DNA from multiple individuals makes using traditional frequency‐based approaches challenging. Here, we explore how eDNA can be used to investigate population structure of Hector's dolphin (Cephalorhynchus hectori), an endemic, endangered, and culturally important (taonga) species. In doing so, we present a simple and effective method to filter out noise due to PCR/sequence error and show how treating haplotype detections equally can provide similar results to frequency‐based approaches from traditional sampling methods. Over the 2022/23 Austral summer, we collected 85 water samples close to Hector's dolphins, and three negative controls, across three areas on the east coast of Aotearoa New Zealand's South Island: Banks Peninsula (n = 41), Timaru (n = 33), and Dunedin (n = 14). We targeted a 348 bp region of the cetacean D‐loop in the mitochondrial DNA (mtDNA) and obtained positive detections in 68 (77%) water samples, confidently identifying seven haplotypes across the study area. The occurrence of specific haplotypes and the overall frequencies in Banks Peninsula and Timaru matched well with previous tissue‐based studies and were similar to other East Coast South Island (ECSI) subpopulations. In Dunedin, however, our results indicate a closer relationship to South Coast populations, suggesting that the membership within the ECSI population be reconsidered, which has implications for how this subpopulation is managed. We show that eDNA sampling can be used to elucidate matrilineal population structure for Hector's dolphin and provide a simple method that could be applied to other eDNA‐based studies of any taxa. We explored how environmental DNA approaches to sampling could be used to explore population genetics questions for Hector's dolphin, an endangered and endemic coastal cetacean. We were successful with isolating known haplotypes from eDNA samples and used this information to reveal novel insights into the subpopulation structuring.

Quantifying the distribution of prey greatly improves models of habitat use by marine predators and can assist in determining threats to both predators and prey. Small epipelagic fishes are important prey for many predators yet their distribution is difficult to quantify due to extreme patchiness. This study explores the use of recreational grade echosounders (RGE) to quantify school characteristics of epipelagic fish and link their distribution to that of their predators at Banks Peninsula, New Zealand. The hydro-acoustic system was ground-truthed with 259 schools of epipelagic fish. During 2015 and 2016, 136 hydro-acoustic surveys were conducted with concurrent observations of Hector's dolphin (Cephalorhynchus hectori) and little penguins (Eudyptula minor). The relative abundance of the two predator species during surveys was modelled according to the relative abundance of potential prey using generalised additive mixed models. Schools of epipelagic fish were readily detected by the RGE system and were more abundant in summer compared to winter. The models performed well, explaining 43% and 37% of the deviance in relative abundances of dolphins and penguins respectively. This is the first study to link the distribution of Hector's dolphin to that of their epipelagic prey and confirms the utility of RGE in studies of habitat use in marine predators. Limitations associated with a lack of formal acoustic calibration and data formatting can be overcome and would make RGE valuable, inexpensive tools for investigating variability in populations of small pelagic fishes.

Understanding the characteristics of hotspots of species distribution provides opportunities for habitat-based management; a vital and often missing component in the conservation of mobile marine species. Correlates of species distribution derived from species distribution models (SDMs) are assumed to represent the characteristics of important habitat, which often include physical and biological (i.e., prey) components. In this study, we integrate surveys of Hector's dolphin (Cephalorhynchus hectori) with in-situ data on environmental characteristics and prey to identify the statistical correlates of distribution and to assess 'what makes hotspots unique'. Between 2014 and 2017, ca. 300 surveys were carried out at hotspots and areas not routinely used by dolphins at Banks Peninsula on the east coast of New Zealand's South Island. A broad range of prey and environmental variables were explored as drivers of dolphin distribution using generalized additive models, and principal component analysis was employed to determine a key environmental signature for hotspots. The relative abundance of dolphins was strongly correlated with prey abundance and a range of environmental variables representing habitat type and oceanographic conditions. The combination of high prey abundance and sandy, shallow, high current and low turbidity habitat was strongly represented at hotspots. These characteristics are also likely attributes of habitat with high ecological value generally, being related to high biodiversity, productivity, naturalness and ecosystem function. This study showcases the importance of targeted investigations into the characteristics of species hotspots to better guide the management of important areas for the conservation of both species and ecosystems.

Gene flow among small fragmented populations is critical for maintaining genetic diversity, and therefore the evolutionary potential of a species. Concern for two New Zealand endemic subspecies, the Hector’s ( Cephalorhynchus hectori hectori ) and Maui’s ( C. h. maui ) dolphins, arises from their low abundance, slow rate of reproduction, and susceptibility to fisheries-related mortality. Our work examined genetic differentiation and migration between the subspecies and among regional and local Hector’s dolphin populations using mitochondrial (mt) DNA and microsatellite genotypes from 438 samples. Results confirmed earlier reports of a single unique mtDNA control region haplotype fixed in the Maui’s dolphin, and provided new evidence of reproductive isolation from Hector’s dolphins (9-locus microsatellite F ST  = 0.167, P  < 0.001). Independent evolutionary trajectories were also supported for Hector’s dolphin populations of the East Coast, West Coast, Te Waewae Bay and Toetoe Bay. Low asymmetrical migration rates were found among several Hector’s dolphin populations and assignment tests identified five Hector’s dolphins likely to have a migrant father from another regional population. There appears to be sufficient step-wise gene flow to maintain genetic diversity within the East and West Coasts; however, the two local South Coast populations exhibited a high degree of differentiation given their close proximity (~100 km). To maintain the evolutionary potential and long-term survival of both subspecies, genetic monitoring and conservation management must focus on maintaining corridors to preserve gene flow and prevent further population fragmentation and loss of genetic diversity, in addition to maintaining local population abundances.

Home range sizes have been determined for few odontocete populations, although the understanding of comparative trends in range utilization is important for conservation. Most of the published knowledge of the Hector's dolphins (Cephalorhynchus hectori) of New Zealand, originates from one well-studied population around Banks Peninsula. Its ranging behavior has been described previously by a decades-long photo-identification (ID) study and by a shorter radio-telemetry study. Little is known, however, about how the dolphins utilize their home range in other coastal areas around the South Island of New Zealand. We used an intensive three-year photo-ID study to define the movement patterns of Hector's dolphins over diel and seasonal scales. Significant differences in the average movement behavior between the East Coast populations off Kaikoura and Moeraki and the West Coast populations off Westport-Greymouth and in Jackson Bay are identified. Movement patterns optimizing range utilization in relation to prey abundance and accessibility are discussed. At the Kaikoura study area, the mean distances between consecutive sightings and speeds of dolphins were considerably reduced compared to other coastal areas. Therefore, the photo-ID study was extended off Kaikoura to cover a total of 14 years. Those findings can be explained by the existence of an environmental barrier (i.e., the deep-water Kaikoura Canyon) that almost completely interrupts Hector's dolphin movements over the short distance of 15 km and very likely has led to a reduced genetic exchange. In conjunction with two recent studies, we present evidence of the impact of an environmental barrier on the population structure and foraging behavior of this shallow-water dolphin.