Reproductive seasonality of a recently designated bottlenose dolphin stock near Charleston,South Carolina,U.S.A

Reproductive seasonality of common bottlenose dolphins (Tursiops truncatus) can be affected by numerous ecological and behavioral factors. In 2009, stock boundaries were revised to recognize a Charleston Estuarine System Stock (CESS) of bottlenose dolphins in Charleston, South Carolina. The CESS is a well‐studied population with long‐term data collected from photo‐identification and stranding studies. From 2004 to 2008, a systematic mark‐recapture photo‐identification study was conducted in the Charleston Estuary to estimate population size of the CESS. Sightings data from this photo‐identification study coupled with strandings data (1993–2008) were analyzed to determine the reproductive seasonality of this local population. Both neonate sightings and strandings depicted a primary season of reproduction in the spring into early summer with a small peak in neonate sightings in early autumn, and were significantly different from circular uniform and Von Mises distributions (strandings: P < 0.01, V = 2.8644; sightings: P < 0.01, V = 3.2302). This study increases the knowledge of seasonal reproductive patterns of estuarine stocks of bottlenose dolphin stocks in the southeastern United States. The results will also help wildlife managers detect unusual neonate mortality events, and provide information about critical habitat relevant for evaluating and mitigating coastal development projects.     

Integrating multiple data sources to assess the distribution and abundance of bottlenose dolphins Tursiops truncatus in Scottish waters

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ABUNDANCE OF SOUTHERN CALIFORNIA COASTAL BOTTLENOSE DOLPHINS ESTIMATED FROM TANDEM AERIAL SURVEYS

We describe a tandem aerial survey method for bottlenose dolphins ( Tursiops truncatus ) that uses two aircraft and independent observer teams to conduct consecutive surveys of the same coastal strip one hour apart. Alternatively, one aircraft with one observer team surveys the same coastal strip twice over several hours. Using mark-recapture analysis, we corrected survey counts for visibility bias resulting from missing dolphin groups at the surface and submerged groups. Dolphin groups were considered "recaptured" when we determined that both observer teams had detected the same group. This tandem method is highly useful for estimating abundance (and visibility bias) for species where population closure may be assumed between flights. We assumed population closure between flights and matched groups using geographic location, group size, and expected travel rates. We derive a new variance estimator of population size which incorporates group-size variability commonly encounteted in cetacean surveys. From six tandem surveys conducted from 1991 to 1994, we estimated the abundance of southern California coastal bottlenose dolphins to be between 78 (95% CI 60-102) and 271 (240-306) animals, with an average of 140 (128-154). Variability in abundance estimates is likely due to seasonal and interannual movement of animals along the California and Baja California coast. Abundance estimates from tandem surveys averaged 53% higher than dolphin counts obtained from individual survey flights, demonstrating the importance of correcting for visibility bias.     

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment

While the population growth rate in long‐lived species is highly sensitive to adult survival, reproduction can also significantly drive population dynamics. Reproductive parameters can be challenging to estimate as breeders and nonbreeders may vary in resighting probability and reproductive status may be difficult to assess. We extended capture–recapture (CR) models previously fitted for data on other long‐lived marine mammals to estimate demographic parameters while accounting for detection heterogeneity between individuals and state uncertainty regarding reproductive status. We applied this model to data on 106 adult female bottlenose dolphins observed over 13 years. The detection probability differed depending on breeding status. Concerning state uncertainty, offspring were not always sighted with their mother, and older calves were easier to detect than young‐of‐the‐year (YOY), respectively, 0.79 (95% CI 0.59–0.90) and 0.58 (95% CI 0.46–0.68). This possibly led to inaccurate reproductive status assignment of females. Adult female survival probability was high (0.97 CI 95% 0.96–0.98) and did not differ according to breeding status. Young‐of‐the‐year and 1‐year‐old calves had a significantly higher survival rate than 2‐year‐old (respectively, 0.66 CI 95% 0.50–0.78 and 0.45 CI 95% 0.29–0.61). This reduced survival is probably related to weaning, a period during which young are exposed to more risks since they lose protection and feeding from the mother. The probability of having a new YOY was high for breeding females that had raised a calf to the age of 3 or lost a 2‐year‐old calf (0.71, CI 95% 0.45–0.88). Yet, this probability was much lower for nonbreeding females and breeding females that had lost a YOY or a 1‐year‐old calf (0.33, 95% CI 0.26–0.42). The multievent CR framework we used is highly flexible and could be easily modified for other study questions or taxa (marine or terrestrial) aimed at modeling reproductive parameters.     

Population structure of island‐associated dolphins: Evidence from mitochondrial and microsatellite markers for common bottlenose dolphins (Tursiops truncatus) around the main Hawaiian Islands

We used mitochondrial and nuclear genetic markers to investigate population structure of common bottlenose dolphins, Tursiops truncatus, around the main Hawaiian Islands. Though broadly distributed throughout the world's oceans, bottlenose dolphins are known to form small populations in coastal waters. Recent photo‐identification data suggest the same is true in Hawaiian waters. We found genetic differentiation among (mtDNA Φ_ST= 0.014–0.141, microsatellite F’_ST= 0.019–0.050) and low dispersal rates between (0.17–5.77 dispersers per generation) the main Hawaiian Island groups. Our results are consistent with movement rates estimated from photo‐identification data and suggest that each island group supports a demographically independent population. Inclusion in our analyses of samples collected near Palmyra Atoll provided evidence that the Hawaiian Islands are also occasionally visited by members of a genetically distinct, pelagic population. Two of our samples exhibited evidence of partial ancestry from Indo‐Pacific bottlenose dolphins (T. aduncus), a species not known to inhabit the Hawaiian Archipelago. Our findings have important implications for the management of Hawaiian bottlenose dolphins and raise concerns about the vulnerability to human impacts of pelagic species in island ecosystems.     

Genetic differentiation among coastal and offshore common bottlenose dolphins,Tursiops truncatus,in the eastern North Pacific Ocean

Common bottlenose dolphins (Tursiops truncatus) are found worldwide in temperate and tropical regions, often occurring as distinct coastal and offshore ecotypes. Along the west coast of the United States, two stocks are recognized for management based on morphological and photo‐identification studies: a California coastal stock, estimated at 450–500 individuals, and a California/Oregon/Washington offshore stock of about 1,000 animals. This study is the first to analyze genetic differentiation between these stocks. We examined both the hypervariable portion of the mitochondrial DNA (mtDNA) control region and fifteen microsatellite markers for coastal (n = 64) and offshore (n = 69) dolphins. Significant genetic differentiation was found between the two stocks for mtDNA (Φ_ST = 0.30, P < 0.001; F_ST = 0.14, P < 0.001) and microsatellite loci (F_ST = 0.19, P < 0.001). Coastal dolphins had less genetic diversity than offshore dolphins. Further substructuring within the offshore stock was not detected. The level of genetic differentiation between the coastal and offshore dolphins is consistent with long‐term separation and reinforces recognizing them as separate stocks. These findings are particularly important for management of the smaller, less genetically diverse, coastal stock that is vulnerable to a variety of anthropogenic threats.     

Site fidelity,residency, and abundance of bottlenose dolphins (Tursiops sp.) in Adelaide's coastal waters,South Australia

Little is known about the ecology and behavior of southern Australian bottlenose dolphins (Tursiops sp.). This hinders assessment of their conservation status and informed decision‐making concerning their management. We used boat‐based surveys and photo‐identification data to investigate site fidelity, residency patterns, and the abundance of southern Australian bottlenose dolphins in Adelaide's coastal waters. Sighting rates and site fidelity varied amongst individuals, and agglomerative hierarchical cluster analysis led to the categorization of individuals into one of three groups: occasional visitors, seasonal residents, or year‐round residents. Lagged identification rates indicated that these dolphins used the study area regularly from year to year following a model of emigration and reimmigration. Abundance estimates obtained from multisample closed capture‐recapture models ranged from 95 individuals (SE ± 45.20) in winter 2013 to 239 (SE ± 54.91) in summer 2014. The varying levels of site fidelity and residency, and the relatively high number of dolphins found throughout the study area highlights the Adelaide metropolitan coast as an important habitat for bottlenose dolphins. As these dolphins also appear to spend considerable time outside the study area, future research, conservation, and management efforts on this population must take into account anthropogenic activities within Adelaide's coastal waters and their adjacencies.     

Patterns of mortality in endangered Cook Inlet beluga whales: Insights from pairing a long-term photo-identification study with stranding records

Mortality is a demographic metric crucial for understanding the dynamics of endangered populations such as Cook Inlet beluga whales (CIBWs, Delphinapterus leucas), but patterns of mortality are currently not well understood for CIBWs, making decisions about recovery actions challenging. We combined long-term photo-ID data from approximately 420 individual belugas identified during the period 2005–2017 with stranding data from 95 dead belugas to identify patterns of mortality with respect to age, sex, geographic range, cause of death, and to estimate minimum mortality rates. Reported mortality was greatest for adults of reproductive age, followed by calves, with fewer subadults and no adults older than 49 years in the stranding data set despite lifespans of 70+ years reported in other beluga populations. Dead females and males were evenly represented. Live stranding was the predominant assigned cause of death but represented only ~33% of deaths of known cause. Causal factors for the majority of deaths and live strandings are unknown. Annual mortality estimated from reported carcasses relative to total population size averaged 2.2%. Our analysis advances our current understanding of mortality patterns in CIBWs but linking a greater proportion of carcasses to photo-ID individuals would further improve our understanding; we conclude with recommendations for achieving this.     

RANGE CHARACTERISTICS OF PACIFIC COAST BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) IN THE SOUTHERN CALIFORNIA BIGHT

Boat-based photoidentification surveys of bottlenose dolphins (Tursiops truncatus) were conducted from 1982 to 1989 in three discrete coastal study areas within the Southern California Bight: (1) Santa Barbara, California; (2) Orange County, California; (3) Ensenada, Baja California, Mexico. A total of 207 recognizable dolphins were identified in these three “secondary” study areas. These individuals were compared to 404 dolphins identified from 1981 to 1989 in our “primary” study area, San Diego, California, to examine the coastal movement patterns of bottlenose dolphins within the Southern California Bight. A high proportion of dolphins photographed in Santa Barbara (88%), Orange County (92%), and Ensenada (88%) were also photographed in San Diego. Fifty-eight percent (n= 120) of these 207 dolphins exhibited back-and-forth movements between study areas, with no evidence of site fidelity to any particular region. Minimum range estimates were 50 and 470 km. Minimum travel-speed estimates were 11-47 km/d, and all dolphin schools sighted during the study were within 1 km of the shore. These data suggest that bottlenose dolphins within the Southern California Bight are highly mobile within a relatively narrow coastal zone. Home-range dimensions and movement patterns for many vettebrate species are influenced, in part, by variation in food resources. The unique range characteristics documented during this study may reflect the highly dynamic nature of this coastal ecosystem and the associated patchy distribution of food resources available to these bottlenose dolphins.     

Seasonal abundance and adult survival of bottlenose dolphins (Tursiops truncatus) in a community that cooperatively forages with fishermen in southern Brazil

A subgroup of a population of Tursiops truncatus in southern Brazil is known for a cooperative behavior with artisanal fishermen whereby the dolphins shoal fish towards net‐casting fishermen. Combining photo‐identification data collected between September 2007 and 2009 with mark‐recapture and Pollock's robust design models, we assessed abundance within seasons and survival and temporary emigration rates of dolphins between seasons. We also reanalyzed a previous data set collected during 1989–1991, and Cormack‐Jolly‐Seber models were applied to estimate survival rates for each of the study periods. The abundance of marked “cooperative” dolphins varied between seasons from 18 (CI: 17–24) to 21 (CI: 20–24). The total abundance varied from 59 in the winter of 2008 (CI: 49–72) to 50 in the autumn of 2009 (CI: 40–62). The annual adult survival was estimated to be 0.917 (CI: 0.876–0.961), close to that estimated from data collected in the 1990s (0.941; CI: 0.888–0.998). The emigration probability was low (0.031; CI: 0.011–0.084) and different capture probabilities between the “cooperative” and “noncooperative” dolphins indicated a degree of behavioral segregation. The precision of our estimates is likely to provide sufficient power to detect population change, but we recommend a precautionary management approach to protect this vulnerable dolphin community and its unique cooperative feeding tradition.     

Using distance sampling techniques to estimate bottlenose dolphin (Tursiops truncatus) abundance at Turneffe Atoll,Belize

Reliable abundance estimates are critical for management and conservation of coastal small cetaceans. This is particularly important in developing countries where coastal human populations are increasing, the impacts of anthropogenic activities are often unknown, and the resources necessary to assess coastal cetaceans are limited. We adapted ship‐based line transect methods to small‐boat surveys to estimate the abundance of bottlenose dolphins (Tursiops truncatus) at Turneffe Atoll, Belize. Using a systematic survey design with random start and uniform coverage, 34 dolphin clusters were sighted during small‐boat line transect surveys conducted in 2005–2006. Distance sampling methods estimated abundance at 216 individuals (CV = 27.7%, 95% CI = 126–370). Due to species rarity in the Atoll, small sample size, and potential violations in line transect assumptions, the estimate should be considered preliminary. Nevertheless, it provides up‐to‐date information on the status of a regional population in an area under increasing threat of habitat loss and prey depletion via uncontrolled development and unsustainable fishing. This information will be useful as Belize develops a new conservation initiative to create a comprehensive and resilient marine protected area system. Our study illustrates the application of distance sampling methods to small‐boat surveys to obtain abundance estimates of coastal cetaceans in a region lacking resources.     

Restricted dispersal in a continuously distributed marine species: common bottlenose dolphins Tursiops truncatus in coastal waters of the western North Atlantic

The marine environment provides an opportunity to examine population structure in species with high dispersal capabilities and often no obvious barriers to genetic exchange. In coastal waters of the western North Atlantic, common bottlenose dolphins, Tursiops truncatus, are a highly mobile species with a continuous distribution from New York to Florida. We examine if the highly mobile nature coupled with no obvious geographic barriers to movement in this region result in a large panmictic population. Mitochondrial control region sequences and 18 microsatellite loci indicate dolphins are partitioning the habitat both latitudinally and longitudinally. A minimum of five genetically differentiated populations were identified among 404 samples collected in the range of New Jersey to northern Florida using both genetic marker types, some inhabiting nearshore coastal waters and others utilizing inshore estuarine waters. The genetic results reject the hypothesis of a single stock of coastal bottlenose dolphins put forth after the 1987–1988 epizootic that caused a large‐scale die‐off of dolphins and suggest instead the disease vector was transferred from one population to the next as a result of seasonal migratory movements of some populations. These coastal Atlantic populations also differ significantly from bottlenose dolphin samples collected in coastal waters of the northern Gulf of Mexico, implying a long‐term barrier to movement between the two basins.     

Skin lesion prevalence of estuarine common bottlenose dolphins (Tursiops truncatus) in North Carolina,with comparisons to other east coast study sites

Common bottlenose dolphins (Tursiops truncatus) are sentinels of environmental health. Skin lesions may indicate disease and can be used to infer population health. We estimated the prevalence of skin lesions and identified major lesion types on coastal bottlenose dolphins in Roanoke Sound, North Carolina, over a 3-year period using photo-identification. Boat-based surveys were conducted from April 2012 through October 2014. High quality images of distinctive fins were examined for overall prevalence (P) of any skin lesion (n = 169, P = 0.49, 95% CI = 0.42–0.57). Lesion prevalence estimates varied little between years (2012 P = 0.45, 2013 P = 0.56, 2014 P = 0.52) and most lesions were observed in the spring (P = 0.79, 95% CI: 0.57–0.92). Of six lesion types examined, pale lesions were most common (P = 0.41, 95% CI: 0.30–0.52). Annual lesion prevalence estimates for dolphins in Roanoke Sound were comparable to published estimates for T. truncatus in Charleston, South Carolina, Brunswick, Georgia, and Sarasota, Florida (p ≥ .05), although, seasonal differences in lesion occurrence and type were observed (p < .05). Future studies should examine relationships between lesions and environmental variables and use stranded dolphins to investigate skin lesion etiology.     

Mark‐resight abundance and survival estimation of Indo‐Pacific bottlenose dolphins,Tursiops aduncus,in the Swatch‐of‐No‐Ground,Bangladesh

A mark‐resight analysis under Pollock's robust design was applied to Indo‐Pacific bottlenose dolphins Tursiops aduncus in the Swatch‐of‐No‐Ground (SoNG) submarine canyon, Bangladesh, during the winter seasons of 2005–2009. Information from sightings of photo‐identified individuals (1,144) and unmarked individuals generated abundance estimates of 1,701 (95% confidence interval [CI]= 1,533–1,888), 1,927 (95% CI = 1,851–2,006), 2,150 (95% CI = 1,906–2,425), and 2,239 (95% CI = 1,985–2,524) individuals for seasons 1–4, respectively. This makes the population among the largest assessed of the species. Overall apparent survival was estimated as 0.958 (95% CI = 0.802–0.992). Interseasonal probabilities of transitioning to an unobservable state were estimated as 0.045, 0.363, and 0.300 for years 1–2, 2–3, and 3–4, respectively, and the overall probability of remaining in an unobservable state was 0.688. These probabilities, together with an apparent increase in abundance during the study period, indicate that the identified dolphins are part of a larger superpopulation moving throughout a more extensive geographic area. Of the photo‐identified dolphins, 28.2% exhibited injuries related to entanglements with fishing gear. This implies a strong potential for fatal interactions that could jeopardize the conservation status of the population, which otherwise appears favorable.     

Insights from life history traits of Risso's dolphins (Grampus griseus) in Taiwanese waters: Shorter body length characterizes northwest Pacific population

Risso's dolphins (Grampus griseus) are widely distributed throughout temperate to tropical pelagic waters of the world and are one of the most frequently encountered cetaceans in eastern Taiwanese coastal waters. Because their life history is poorly known, the goal of this study was to investigate the relationship between age, body length, and sexual maturity of Risso's dolphins in Taiwanese waters. Ninety‐two carcasses of dead‐stranded or fisheries bycaught dolphins (1994–2008) were measured and dissected (total body length, TBL 125–290 cm); sexual maturity was assessed in 33 dolphins; and age was estimated by counting dentinal growth layer groups in routine histologically prepared tooth sections of 28 dolphins. Sexual dimorphism in TBL was not detected. The onset of sexual maturity occurred at 240–255 cm in females and 253–265 cm in males, which was at about 10 yr of age for both sexes. Our stranding, bycatch, and previous boat survey records suggest that Risso's dolphins occur year‐round and likely have a summer‐fall calving season in Taiwanese waters. The similar life history parameters and calving season in dolphins from Taiwanese and Japanese waters suggest a common population in the northwest Pacific, which has a noticeably shorter body length than in other regions.     

Inferring causal factors for a declining population of bottlenose dolphins via temporal symmetry capture–recapture modeling

We applied temporal symmetry capture–recapture (TSCR) models to assess the strength of evidence for factors potentially responsible for population decline in bottlenose dolphins (Tursiops truncatus) in Doubtful Sound, New Zealand from 1995 to 2008. Model selection was conducted to estimate recruitment and population growth rates. There were similar levels of support for three different models, each reflecting distinct trends in recruitment. Modeling yielded low overall estimates of recruitment (0.0249, 95% CI: 0.0174–0.0324) and population growth rate (0.9642, 95% CI: 0.9546–0.9737). The TSCR rate of population decline was consistent with an estimate derived from trends in abundance (lambda = 0.9632, 95% CI: 0.9599–0.9665). The TSCR model selection confirmed the influence of a decline in the survival of calves (<1 yr old) since 2002 for population trends. However, TSCR population growth rates did not exceed 1 in any year between 1995 and 2008, indicating the population was declining prior to 2002. A separate reduction in juvenile survival (1–3 yr old) prior to 2002 was identified as a likely contributing factor in the population decline. Thus, TSCR modeling indicated the potential cause of the population decline in Doubtful Sound: cumulative impacts on individuals <3 yr old resulting in a reduced recruitment.     

High calf mortality in bottlenose dolphins in the Bay of Islands,New Zealand–a local unit in decline

Bottlenose dolphins (Tursiops truncatus) in the Bay of Islands, New Zealand, have been studied for almost two decades. Since 2003, fewer than 150 dolphins visited the bay during each season and the local unit has declined 7.5% annually from 1997 to 2006. The causes of decline are unclear but probably include mortality and emigration. Here, we used a long‐term database to estimate reproductive parameters of female bottlenose dolphins including recruitment rates. A total of 704 surveys were conducted in which 5,577 sightings of 408 individually identified dolphins were collected; of these 53 individuals were identified as reproductive females. The calving rate increased between periods (1997–1999 = 0.13, CL = 0.07–0.21; 2003–2005 = 0.25, CL = 0.16–0.35 calves/reproductive female/year). A 0.25 calving rate suggests that on average, a female gives birth only once every four years, which is consistent with the estimated calving interval (4.3 yr, SD = 1.45) but still is lower than values reported for other populations. Conversely, apparent mortality rates to age 1+ (range: 0.34–0.52) and 2+ (range: 0.15–0.59) were higher than values reported elsewhere. The high apparent calf mortality in conjunction with a decline in local abundance, highlight the vulnerability of bottlenose dolphins in the Bay of Islands. Long‐term studies are required to understand the causes of high calf mortality and the decline in local abundance. Meanwhile, management should focus on minimizing sources of anthropogenic disturbance and enforcing compliance with current legislation.     

Genetic isolation between coastal and fishery‐impacted,offshore bottlenose dolphin (Tursiops spp.) populations

The identification of species and population boundaries is important in both evolutionary and conservation biology. In recent years, new population genetic and computational methods for estimating population parameters and testing hypotheses in a quantitative manner have emerged. Using a Bayesian framework and a quantitative model‐testing approach, we evaluated the species status and genetic connectedness of bottlenose dolphin (Tursiops spp.) populations off remote northwestern Australia, with a focus on pelagic ‘offshore’ dolphins subject to incidental capture in a trawl fishery. We analysed 71 dolphin samples from three sites beyond the 50 m depth contour (the inshore boundary of the fishery) and up to 170 km offshore, including incidentally caught and free‐ranging individuals associating with trawl vessels, and 273 dolphins sampled at 12 coastal sites inshore of the 50 m depth contour and within 10 km of the coast. Results from 19 nuclear microsatellite markers showed significant population structure between dolphins from within the fishery and coastal sites, but also among dolphins from coastal sites, identifying three coastal populations. Moreover, we found no current or historic gene flow into the offshore population in the region of the fishery, indicating a complete lack of recruitment from coastal sites. Mitochondrial DNA corroborated our findings of genetic isolation between dolphins from the offshore population and coastal sites. Most offshore individuals formed a monophyletic clade with common bottlenose dolphins (T. truncatus), while all 273 individuals sampled coastally formed a well‐supported clade of Indo‐Pacific bottlenose dolphins (T. aduncus). By including a quantitative modelling approach, our study explicitly took evolutionary processes into account for informing the conservation and management of protected species. As such, it may serve as a template for other, similarly inaccessible study populations.     

“Porpicide” in California: Killing of harbor porpoises (Phocoena phocoena) by coastal bottlenose dolphins (Tursiops truncatus)

Between 2007 and 2009, we witnessed three aggressive interactions between harbor porpoises and bottlenose dolphins in Monterey Bay, California. This is the first time such aggression has been documented in the Pacific, and the first time a harbor porpoise was collected immediately after witnessing its death, inflicted by bottlenose dolphins. Of the bottlenose dolphins present, 92% were males either confirmed (61%) or putative (31%). Since 2005, 44 harbor porpoise deaths inflicted by bottlenose dolphins were documented in California. Aberrant behavior was rejected as a cause of aggression, based on widespread documentation of similar behaviors in other populations of free‐ranging bottlenose dolphins. The evidence for interspecies territoriality as a form of competition for prey was weak: there is little dietary overlap and there are differences in bottlenose dolphin and harbor porpoise distribution patterns in California. Object‐oriented play was plausible as a form of practice to maintain intraspecific infanticidal skills or a form of play to maintain fighting skills between male associates. Contributing factors could be high‐testosterone levels, as attacks occurred at the height of the breeding season, and/or a skewed operational sex ratio. Ultimately, we need more information about bottlenose dolphin social structure at the time of the aggression.