High genetic differentiation of Indo‐Pacific humpback dolphins (Sousa chinensis) along the Asian Coast of the Pacific Ocean

The Indo‐Pacific humpback dolphin (Sousa chinensis) is a vulnerable marine mammal species that inhabits shallow, coastal waters from Southeast China, southward throughout Southeast Asia, and westward around the Bay of Bengal to eastern India. Polymorphic microsatellites are useful for elucidating ecological and population genetics‐related questions. Here, 18 new polymorphic microsatellites were developed from S. chinensis genomic DNA by Illumina MiSeq sequencing. Population genetic analyses were conducted on 42 S. chinensis individuals from three geographic locations, including the Xiamen Bay of China, the Western Gulf of Thailand, and Andaman Sea. Our microsatellite data revealed a strong and significant population structure among the three sampling regions (overall F _ST = 0.371, p = .001). Pairwise mutual information index also demonstrated high levels of genetic differentiation between different region pairs (values range from 0.272 to 0.339, p < .001). Moreover, Structure analysis inferred three genetic clusters, with the high assignment probabilities of 95.92%, 99.47%, and 99.68%, respectively. Principal coordinate analysis plots of individuals divided entire genotypes into three clusters, indicating high level of genetic differentiation. Our results indicated the strong genetic structure in S. chinensis populations is a result of geographic distances. Other factors such as environmental variables, anthropogenic interference, and social behavior may also have contributed to population differentiation.     

Fine‐scale habitat use in Indo‐Pacific humpback dolphins,Sousa chinensis,may be more influenced by fish rather than vessels in the Pearl River Estuary,China

Shifts in habitat use and distribution patterns in dolphins are often concerns that can result from habitat degradation. We investigated how potential changes to a habitat from human activity may alter dolphin distributions within Lingding Bay in the Pearl River Estuary, China, by studying the relationship between fish choruses, vessel presence and Indo‐Pacific humpback dolphin (Sousa chinensis) detection rates. Analyses revealed temporal and spatial variation within fish choruses, vessel presence and dolphin detection rates. After accounting for any temporal autocorrelation, correlations between fish choruses and dolphin detection rates were also found; however, no relationship between fish choruses and vessel presence or dolphin detection rates and vessel presence were observed. Furthermore, fewer dolphins were detected at sites where fish activity was less intense. Thus fish activity, rather than vessels, may be a key factor influencing the distribution of the dolphins within the estuary. These findings emphasize the risk of potential shifts in habitat use for Indo‐Pacific humpback dolphins due to detrimental changes to prey availability and dolphin feeding grounds from human activity, such as overfishing and coastal developments, within the estuary. This is a critical conservation issue for this dolphin population that is facing intense anthropogenic pressure.     

厦门水域中华白海豚出现于围头湾

厦门海域的中华白海豚是一个受威胁的种群。以往有关该种群的调查范围主要集中在厦门以及邻近的南部漳州海域。为了获得厦门岛东部海域（包括晋江围头湾、小嶝岛以及大嶝岛部分水域）白海豚的分布和数量等信息,本文于2013年6—8月对该水域进行了船基样线法调查和照相识别研究。调查期间共目击到白海豚26群,照相识别白海豚个体27头。所有照相识别的白海豚个体均与厦门中华白海豚个体识别数据库中的个体匹配,表明厦门中华白海豚的分布区至少向东延伸至围头湾。本文白海豚遇见率为5.8群/100km和24.8头/100km,均要高于以往在厦门水域的调查结果,表明大嶝岛—围头湾水域是厦门中华白海豚的重要栖息地之一,值得优先保护和管理。     

Habitat and resource partitioning among Indo‐Pacific bottlenose dolphins in Moreton Bay,Australia

Investigating resource partitioning among mobile marine predators such as cetaceans is challenging. Here we integrate multiple methodologies (analyses of habitat use, stable isotopes and trace elements) to assess ecological niche partitioning amongst two genetically divergent sympatric subpopulations (North and South) of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) in Moreton Bay, Australia. Comparisons of the mean locations (latitude, longitude) and environmental variables (distance from sandbanks, distance from shore and water depth) observed at sightings of biopsy‐sampled individuals indicated that the North subpopulation occurred in the northwestern bay in significantly deeper water than the South subpopulation, which was found in southeastern nearshore waters and closer to sandbanks. Ratios of stable carbon and nitrogen isotopes in skin samples suggested that North dolphins foraged on higher trophic level prey in relatively more pelagic, offshore habitats, while South dolphins foraged on lower trophic prey in more nearshore, demersal and/or benthic habitats. Habitat partitioning was also reflected in higher blubber concentrations of most of the 13 measured trace elements, in particular lead, in the coastal South compared to the more pelagic North dolphins. These findings indicate that genetic subpopulations of bottlenose dolphins in Moreton Bay are adapted to different niches.     

Phylogenetic placement and population structure of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar,Tanzania, based on mtDNA sequences

Phylogenetic placement of bottlenose dolphins from Zanzibar, East Africa and putative population differentiation between animals found off southern and northern Zanzibar were examined using variation in mtDNA control region sequences. Samples (n= 45) from animals bycaught in fishing gear and skin biopsies collected during boat surveys were compared to published sequences (n= 173) of Indo‐Pacific bottlenose dolphin, Tursiops aduncus, from southeast Australian waters, Chinese/Indonesian waters, and South African waters (which recently was proposed as a new species) and to published sequences of common bottlenose dolphin, Tursiops truncatus. Bayesian and maximum parsimony analyses indicated a close relationship between Zanzibar and South African haplotypes, which are differentiated from both Chinese/Indonesian and Australian T. aduncus haplotypes. Our results suggest that the dolphins found off Zanzibar should be classified as T. aduncus alongside the South African animals. Further, analyses of genetic differentiation showed significant separation between the T. aduncus found off northern and southern Zanzibar despite the relatively short distance (approximately 80 km) between these areas. Much less differentiation was found between southern Zanzibar and South Africa, suggesting a more recent common evolutionary history for these populations than for the northern and southern Zanzibar populations.     

Signature whistles in free‐ranging populations of Indo‐Pacific bottlenose dolphins,Tursiops aduncus

Common bottlenose dolphins (Tursiops truncatus) use individually distinctive signature whistles which are highly stereotyped and function as contact calls. Here we investigate whether Indo‐Pacific bottlenose dolphins (T. aduncus) use signature whistles. The frequency trace of whistle contours recorded from three genetically distinct free‐ranging populations was extracted and sorted into whistle types of similar shape using automated categorization. A signature whistle identification method based on the temporal patterns in signature whistle sequences of T. truncatus was used to identify signature whistle types (SWTs). We then compared the degree of variability in SWTs for several whistle parameters to determine which parameters are likely to encode identity information. Additional recordings from two temporarily isolated T. aduncus made during natural entrapment events in 2008 and 2009 were analyzed for the occurrence of SWTs. All populations were found to produce SWTs; 34 SWTs were identified from recordings of free‐ranging T. aduncus and one SWT was prevalent in each recording of the two temporarily isolated individuals. Of the parameters considered, mean frequency and maximum frequency were the least variable and therefore most likely to reflect identity information encoded in frequency modulation patterns. Our results suggest that signature whistles are commonly used by T. aduncus.     

Dispersal,philopatry, and the role of fission‐fusion dynamics in bottlenose dolphins

In this quantitative study of locational and social dispersal at the individual level, we show that bottlenose dolphins (Tursiops sp.) continued to use their natal home ranges well into adulthood. Despite substantial home range overlap, mother–offspring associations decreased after weaning, particularly for sons. These data provide strong evidence for bisexual locational philopatry and mother–son avoidance in bottlenose dolphins. While bisexual locational philopatry offers the benefits of familiar social networks and foraging habitats, the costs of philopatry may be mitigated by reduced mother–offspring association, in which the risk of mother–daughter resource competition and mother–son mating is reduced. Our study highlights the advantages of high fission–fusion dynamics and longitudinal studies, and emphasizes the need for clarity when describing dispersal in this and other species.     

Patterns of seasonal occurrence,distribution, and site fidelity of coastal bottlenose dolphins (Tursiops truncatus) in southern New Jersey,U.S.A.

Coastal bottlenose dolphins (Tursiops truncatus) form a mosaic of resident and seasonal migratory populations along the United States Atlantic seaboard. Seasonal, poorly known migrants (identified as a separate stock) move as far north as New Jersey. During 2003–2005, 73 boat‐based photo‐identification surveys were conducted in southern New Jersey to discern seasonal occurrence, distribution, and patterns of movement and site fidelity. Neonates, young‐of‐year, and adults occurred in the study area from late May through late September, corresponding to water temperatures of 14.0–16.3°C. Of 205 individuals identified, 44% (n= 90) were sighted multiple times within or among years, including 10% (n= 20) of individuals identified in all 3 yr. Almost half (47%) of the multiple sightings were observed along a core area encompassed by the southern part of the Jacques Cousteau National Estuarine Research Reserve. In contrast to stocks studied in southern coastal areas of the U.S. Atlantic and Gulf of Mexico, estuaries were used significantly less than open‐beach habitat, which is consistent with the relative prey abundance in these habitats. Research at additional sites will help confirm whether bottlenose dolphins at the northern end of their migratory range exhibit local site fidelity and habitat preferences similar to those found in this study.     

厦门水域中华白海豚栖息地选择的初步研究

中华白海豚（Sousa chinensis）在中国水域主要包括3个种群,分别分布在珠江口（包括香港）、九龙江口（厦门水域）和北部湾广西沿岸水域,近年来在台湾西海岸和广东的雷州又陆续发现了新的种群（Wang et al．,2004;周开亚等,待发表资料）。该物种主要以中小种群分布于近岸浅水水域,易受各种人类活动的影响,如渔业捕捞、船舶航运、港口建设和水体污染等,其保护状况引起了人们的广泛关注。在1988年颁布的《中华人民共和国野生动物保护法》中,已将该物种列为国家一级保护动物。     

厦门海域两头中华白海豚体内铁的含量

铁是动物体的必需元素,是血红蛋白和肌红蛋白中氧的携带者。动物体内的含铁化合物主要为血红蛋白、肌红蛋白（Mb）、转铁蛋白、含铁血黄素和含铁酶（王夔,1992）。铁与水生哺乳动物的潜水能力密切相关。Wright和Davis（2006）对威德尔海豹（Leptonychotes weddellii）的研究表明,Mb是水生哺乳动物最重要的储氧部位,在胃肠吸收后状态下Mb从正常水平降低7％时,有氧潜水限度（Aerobic Dive Limit,ADL）下降39％;Mb增加两倍时,ADL则增加30％。     

Site fidelity and association patterns in a deep-water dolphin: Rough-toothed dolphins (Steno bredanensis) in the Hawaiian Archipelago

In the Pacific, rough-toothed dolphins ( Steno bredanensis ) are typically found in the open ocean and in deep waters around oceanic islands. We examined habitat use, site fidelity, movements, and association patterns of this species in the main Hawaiian Islands. Sighting rates were highest in depths >1,500 m. There were frequent within- and between-year resightings off the island of Hawai'i, indicating a small population size with high site fidelity. Resighting rates were lower off Kaua'i/Ni'ihau, indicating a larger population size, but with some site fidelity. Two individuals were documented moving from Kaua'i to Hawai'i, a distance of 480 km, but were not seen to associate with dolphins off Hawai'i. Observed movements were consistent with at most 2% dispersal per year between these two areas. Differences in group sizes, habitat use, and behavior imply that movements among the islands may be limited. Little is known about the diet of rough-toothed dolphins in Hawai'i, but they are thought to feed primarily on near-surface species. High fidelity to deep-water areas off the island of Hawai'i likely reflects an increase in the predictability of prey associated with upwelling due to the island mass effect, wind stress curl and cyclonic eddies that form off the island.     

Survival,site fidelity,and the population dynamics of Piping Plovers in Saskatchewan

ABSTRACT To conserve threatened species, managers require predictions about the effects of natural and anthropogenic factors on population growth that in turn require accurate estimates of survival, birth, and dispersal rates, and their correlation with natural and anthropogenic factors. For Piping Plovers (Charadrius melodus), fledging rate is often more amenable to management than adult survival, and population models can be used to estimate the productivity (young produced per breeding female) necessary to maintain or increase populations for given levels of survival. We estimated true survival and site fidelity of adult and subadult (from fledging to second year) Piping Plovers breeding in Saskatchewan using mark‐resight data from 2002 to 2009. By estimating true survival rather than apparent survival (which is confounded with permanent emigration), we were able to provide more accurate projections of population trends. Average adult and subadult survival rates during our study were 0.80 and 0.57, respectively. Adult survival declined over time, possibly due in part to the loss of one breeding site to flooding. Average adult and subadult site fidelity were 0.86 and 0.46, respectively. Adult site fidelity declined during our study at two study sites, most strongly at the flooded site. Male and female Piping Plovers had similar survival rates, but males had greater site fidelity than females in some years. Based on our survival estimates, productivity needed for a stationary population was 0.75, a benchmark used for plover management on the Atlantic Coast, but not previously estimated for Prairie Canada. In stochastic simulations incorporating literature‐based variation in survival rates, productivity needed for a stationary population increased to 0.86, still lower than that previously estimated for western populations. Mean productivity for our study sites ranged from 0.87 to 0.96 fledged young per pair. Our results suggest that fledging rates of Piping Plovers in Saskatchewan were sufficient to ensure a stationary or increasing population during our study period. However, large‐scale habitat changes such as drought or anthropogenic flooding may lead to dispersal of breeding adults and possibly mortality that will increase the fledging rate needed for a stationary population.     

Sex‐related site fidelity of humpback whales (Megaptera novaeangliae) to the Fueguian Archipelago feeding area,Chile

We investigated sex‐related site fidelity by humpback whales to the Fueguian Archipelago, a new feeding area in the eastern South Pacific, by examining the resighting histories of 45 males and 39 females recorded from 2003 to 2012. Results indicated an overall annual return to the feeding area of 74.8%, and annual sex ratio is roughly equal in the population. The probability of an individual being resighted across years and in subsequent years was not significantly different for both males and females, however, the proportion of resighting within a year was significantly higher for individual males compared to females. Potential sources of sex‐related bias were analyzed, but none were found to be significant. Greater intraannual resighting frequency for males may reflect sex‐based differences in spatial occupation and short‐range movements due to potential differences in energy budgets.     

Sonographic evaluation of thyroid morphology during different reproductive events in female Indo‐Pacific bottlenose dolphins,Tursiops aduncus

Thyroid morphology and function are likely affected by the cyclic hormonal environment during different reproductive events in females. The present study was undertaken to evaluate the variation of thyroid morphology at different reproductive events (anestrus, estrus, lactation, and pregnancy) in a captive group of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) measured using sonography. Sonographic examinations of the thyroid gland and ovaries in nine sexually mature female subjects were performed weekly for 2.5 yr. A generalized linear mixed model was used to estimate the effects of the reproductive events for thyroid volume. Reproductive event was found to be a significant predictor for thyroid volume measurement and significant variation in thyroid volume was found between different reproductive events. A significantly larger thyroid volume in lactating females was observed when compared with estrous and anestrous females, possibly due to the high energy requirements and milk production during lactation. Taken together, thyroid volume variation during different reproductive events in female dolphins should be considered so as to obtain a diagnostically meaningful assessment when conducting routine examinations.     

Social dynamics and sexual segregation of Australian humpback dolphins (Sousa sahulensis) in Moreton Bay,Queensland

Understanding the social organization of coastal dolphins, particularly those that reside adjacent to major cities and urbanized regions, is important for understanding the vulnerability of populations to human impacts. We investigated the sexual segregation and social dynamics in a population of Australian humpback dolphins (Sousa sahulensis) inhabiting the near-urban embayment of Moreton Bay, Queensland. Over 160 vessel-based surveys, 148 adults were photographically identified. This included 116 assumed females and 32 assumed males. The population was sexually segregated (SSAS = 0.52, p < .001) and individuals preferred to associate with others of the same sex occupying the same spatial area (p < .025). Association indices between paired males were almost double those of females ($\text{◂=▸}\overline{x}\mathrm{HWI}=0.09$, SD = 0.04 and $\text{◂=▸}\overline{x}\mathrm{HWI}=0.05$, SD = 0.02, respectively). However, females were more gregarious than males and maintained a larger network of associates based on preferred companionships. The social network was also modular with five clusters identified, and a limited number of individuals had a disproportionate influence on connectivity between clusters. This highly fragmented social network implies that the population may be vulnerable to social disruptions from human impacts.     

Social communities and spatiotemporal dynamics of association patterns in estuarine bottlenose dolphins

Network analysis has recently been used to delve into the dynamics of cetacean sociality. Few studies, however, have addressed how habitat shape influences sociality, specifically how linear water bodies constrain the space where individuals might interact. We utilized network and spatiotemporal analyses to investigate association patterns and community structure in a bottlenose dolphin population in a linear estuarine system, the Indian River Lagoon (IRL), Florida. Using sighting histories from a multiyear photo‐identification study we examined association patterns for 185 individuals collected over a 6.5 yr period (2002–2008). The population was highly differentiated (S = 0.723) and organized into six distinct social communities (Q = 0.544), spread in an overlapping pattern along the linear system. Social organization differed between communities, with some displaying highly interconnected networks and others comprising loosely affiliated individuals with more ephemeral associations. Temporal patterns indicated short‐term associations were a significant feature of the fission‐fusion dynamics of this population. Spatial analyses revealed that social structure was shaped by an individual's ranging patterns and by social processes including preference and avoidance behavior. Finally, we found that habitat “narrowness” may be a major driving force behind the sociality observed.     

Sexual maturity and estimated fecundity in female Indo‐Pacific bottlenose dolphins (Tursiops aduncus) from South Australia: Combining field observations and postmortem results

Knowledge of life history of bottlenose dolphins in Australia is limited, with no studies comparing field and postmortem data from the same region. Carcasses of 88 opportunistically collected females (1987–2015) were studied, including eight observed for up to 23 yr before death. Ovaries were weighed and number of corpora determined grossly. Nineteen mammary glands were examined histologically. Relative age was determined using developmental features and body length, estimated age by tooth incremental lines, and physical maturity by epiphyseal fusion. Age at sexual maturation was 7.17 yr (6–>14 yr) at body lengths of 191–209 cm. Physical maturation occurred at 12–17 yr, and body lengths of 195–233 cm. An Exponential model provided the best fit for age at body length, with an asymptote at 214 cm. Combined ovary weight increased between birth and sexual maturation, with significantly more corpora in the left ovary. Corpora increased with age and appeared to persist throughout life. For mature females, 95% had ≤ 11 corpora. Number of corpora was consistent with number of calves for females with known life histories. Estimated interbirth period was about 4 yr. Three females with abnormal reproductive features were either chronically diseased and/or had high heavy metal burdens.     

Occurrence,site fidelity,and associations of oceanic common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand

Two ecotypes of the common bottlenose dolphin (Tursiops truncatus) occur in New Zealand waters: a widely studied Nationally Endangered coastal ecotype and a little-known oceanic ecotype. Site fidelity and association patterns of the oceanic ecotype, and home range overlap with the coastal ecotype, are examined from photo-identification records collected off northeastern New Zealand between 2005 and 2016. The oceanic ecotype occurs widely in the study area: distance from shore ranged from <1 to ~150 km and home ranges of the two ecotypes overlap in some areas. Forty-nine percent of the 478 identified distinctive or very distinctive individuals were sighted during more than 1 year and resightings spanned over 10 years and 650 km. All individuals were linked by association in a single, albeit clustered, social network. Unlike the coastal ecotype, interspecific associations with false killer (Pseudorca crassidens) and southern long-finned pilot whales (Globicephala melas edwardii) were frequent, occurring during 84% of encounters. Only one oceanic individual matched any of the individuals from the coastal ecotype photo-identification catalogues throughout the study area, suggesting that the two ecotypes co-occur parapatrically. We recommend that the two ecotypes be considered independent management units for conservation purposes due to their divergent ecologies.