Stenella Longirostris Research Articles

Identification of key discriminating variables between spinner dolphin (Stenella longirostris) whistle types.

Descriptions of the six different spinner dolphin (Stenella longirostris) whistle types were developed from a random sample of 600 whistles collected across a 2-yr period from a Fijian spinner dolphin population. An exploratory multivariate visualization suggested an inverse relationship between delta and minimum frequency (58.6%) as well as whistle duration (18.1%) as the most discriminating variables in this dataset. All three of these variables were deemed to be significant when considered jointly in a multivariate analysis of variance (MANOVA): delta frequency (F5594 = 27.167, p < 0.0001), minimum frequency (F5594 = 14.889, p < 0.0001), and duration (F5594 = 24.303, p < 0.0001). Significant differences between at least two of the whistle types were found for all five acoustic parameters in univariate analysis of variation (ANOVA) tests. Constant and sine whistles were found to be the most distinctive whistles, whereas upsweep and downsweep whistles were the most similar. The identification of which parameters differ most markedly between whistle types and the relatively high explanatory power of this study's results provide a logical starting point for objective classification of spinner dolphin whistle types using machine learning techniques.

Dolphin watching tourists in Fernando de Noronha, Brazil: knowledge and conservation

The components of interpretation and education in whale/dolphin watching tours, besides providing leisure to the participants, are involved in the satisfaction and creation of an environmental awareness. This study aimed to understand the perception, learning and tendency to conservation attitudes of the participants of dolphin-watching in Fernando de Noronha (FN). Were applied 140 questionnaires with tourists after participating in dolphin watching tours in FN. Participants living in the southeastern region of Brazil (57.9%) and with College education (88.6%) were the majority among respondents. Although the dolphin is the main marketing figure for tourism in FN, “sun and beach” tourism was the most cited reason for the trip. The satisfaction declared by respondents was high for both the “Dolphins's Deck” (viewing platform) (94.4%) and the boat tour (83.1%). Respondents visiting the “Dolphins's Deck”, where the educational component is most evident, tended to provide more correct answers related to knowledge and legislation towards dolphins protection in FN. The opportunity to observe a charismatic animal in a natural environment, as occurs with the spinner dolphin in FN, makes it easier for tourist guides and managers to access the affective component of tourists. Providing clear and objective information for tourists may promote long-term changes in their behavior and attitude and contribute to the spinner dolphin protection and to the archipelago preservation.

Cashing in on Spinners: Revenue Estimates of Wild Dolphin-Swim Tourism in the Hawaiian Islands

Wild dolphin-swim tourism has grown in specific locations where Hawaiian spinner dolphins (Stenella longirostris) have known resting habitat. The increased growth in dolphin-swim businesses has created an industry in Hawaii that earns an estimated $102 million (USD) annually in 2013. Semi-structured interviews with business owners, market research, and boat-based observations provide a platform for estimating revenue generated from dolphin tourism in two popular locations, Waianae, Oahu and Kailua-Kona, Hawaii Island. A revenue analysis of dolphin-swim tourism is presented using a peak season and utilization rate model. These predictions offer an accountability exercise based on a series of assumptions regarding wild dolphin-swim demand and an annual estimate of the number of viewing participants and revenue earned. The results show that dolphin viewing companies are making a larger profit than dolphin-swim businesses by approximately $19 million (USD) per year, however, both avenues are generating large earnings. Sizable differences between businesses in Kona and Waianae are discussed. The average lifetime revenue generated by a dolphin in 2013 is estimated at $3,364,316 (USD) for Waianae and $1,608,882 (USD) for Kona, and is presented as a first step in scenario analysis for policy makers looking to implement management in the bays where tourism occurs. This study offers the first revenue estimates of spinner dolphin tourism in Hawaii, which can provide context for further discussion on the impact and economic role of the dolphin-swim industry in the state.

Identifying spinner dolphin Stenella longirostris longirostris movement and behavioral patterns to inform conservation strategies in Maui Nui, Hawai‘i

Spinner dolphins Stenella longirostris longirostris in Hawai‘i exhibit a predictable diurnal behavioral pattern which makes them vulnerable to human disturbance: feeding at night in offshore waters and resting during daytime in bays. There is concern that human activity, such as swimming with and viewing wild dolphins from vessels, is altering their natural behavioral patterns and preventing them from having adequate rest. In light of this, state and federal management agencies are proposing enhanced protection measures. Research on spinner dolphins has largely focused off Hawai‘i Island and there are insufficient data from Maui Nui (Maui, Lāna‘i, Kaho‘olawe, and Moloka‘i) to inform appropriate management measures for the genetically distinct stock that resides around these islands. Using location data from 316 encounters between 1996 and 2019, we identified 2 hotspots for spinner dolphins within the region, located along west Maui and south Lāna‘i. The predominant behavior observed was traveling, and there was little resting behavior documented throughout the study period, with no resting behavior observed along the coastline of Maui. Our findings revealed that spinner dolphins use a wide variety of available habitat in Maui Nui and were observed resting both near the shore of Lāna‘i and in the channels between islands. Based upon these findings, the proposed lone area for closure in south Maui is inadequate for providing protection to spinner dolphins during resting hours, and we propose that the identified hotspots be considered as additional sites for closures, in addition to an approach limit for vessels transiting Maui Nui.

Effects of swim‐with‐dolphin tourism on the behaviour of spinner dolphins, at Samadai Reef in the Egyptian Red Sea

Abstract Spinner dolphins, Stenella longirostris, are the primary target for marine mammal tourism in Egypt. The present study investigated the short‐term effects of tourist presence on the behaviour of spinner dolphins at Sha'ab Samadai (Samadai Reef), in the southern Egyptian Red Sea. The reef has a large central lagoon where a population of spinner dolphin regularly rest from mid‐morning to mid‐afternoon; visitors are permitted to snorkel in the southern part of the lagoon, but not in the northern closed zone that the dolphins mainly use. Dolphin behaviour was monitored both on days when tourist boats were present and on days when they were absent. In the presence of tourists the proportion of time that the dolphins spent resting was reduced by two‐thirds, whereas the times spent milling, travelling, and showing avoidance behaviour all increased. Furthermore, upon using Markov chain modelling to investigate the effect of tourist presence on the transition probabilities between dolphin activity states, significant changes were found in 10 of the 25 possible behavioural transitions, including increased probabilities of transitioning from resting to milling or travelling, from milling to travelling or avoiding, and from travelling to avoiding. These findings raise concerns that despite the management measures in place, tourist activities affect the dolphins’ behaviour to a greater extent than was previously apparent, with potential long‐term negative effects on their energy budget. The study led to proposals for amending the zoning of the site and for strengthening the regulations for tourist vessels.

Low mtDNA diversity in a highly differentiated population of spinner dolphins (Stenella longirostris) from the Fernando de Noronha Archipelago, Brazil.

Spinner dolphins (Stenella longirostris, Gray 1828) are widely distributed in tropical waters around the world. Although they occur in large, pelagic groups in the Eastern Tropical Pacific, elsewhere in the Pacific they are found in small and genetically isolated populations associated with islands. This species is considered to be “Least Concern” (LC) by the World Conservation Union (IUCN). To assess genetic diversity and population structure of an island-associated population in the South Atlantic Ocean we surveyed 162 spinner dolphins throughout the Fernando de Noronha Archipelago of the northeast coast of Brazil using ten microsatellite loci and sequencing a 413-bp section of the mitochondrial DNA (mtDNA) control region. Eleven mtDNA haplotypes were identified and haplotype diversity (h) and nucleotide diversity (π) were 0.3747 and 0.0060, respectively. Median-Joining Network revealed the presence of two very divergent haplotypes and F-statistics indicated some heterogeneity between two sampling years. All microsatellite loci were polymorphic (Ho: 0.767; He: 0,764) but, revealed no detectable substructure. We also compared the mtDNA haplotypes from Noronha to 159 haplotypes representing 893 individuals from 14 locations worldwide. We found that the two common haplotypes from the Fernando de Noronha Archipelago were absent in all other populations. These comparisons showed that Noronha spinner dolphins are likely more differentiated than other island populations, suggesting that they form societies with strong site fidelity mediated by females.

The Formation and Position of Middle Ear Ossicles During Development in Cetacea

The order Cetacea (dolphins, whales, and porpoises) evolved from terrestrial artiodactyls (even‐toed ungulates) around 50 million years ago. This transition from land to water occurred over an evolutionarily short period of less than 10 million years and is considered one of the best examples of macroevolutionary change among vertebrates. Among the sensory systems, the ear has developed a number of unique adaptations to adapt to water borne sounds. We hypothesize that a record of these evolutionary changes is preserved in the prenatal ontogeny. In particular, previous studies on fossils have identified a rotation of the middle ear ossicles with regard to the median plane, as well as a deflection of the axis of the cochlea. It is not clear whether these two movements are related to each other. The purpose of this study is to investigate middle ear development within odontocetes (toothed whales) using two species of dolphin (Stenella attenuata and stenella longirostris). Using Amira and Avizo 3‐D software we investigate the malleus, incus, and stapes over a range of embryological stages and their relationship to inner ear structures, such as the cochlea and semicircular canals. These data are then compared to what is known for adult Stenella.Data is collected on histological sections and CTs of heads of embryologic and fetal specimens. These specimens have either been stained using phosphotungstic acid and microCT scanned (stored in 70% ethanol) or sliced at 7μm and stained using hematoxylin and eosin. We photograph histologic specimens (every other slice) in the region containing the middle and inner ear structures. Avizo and Amira software version 2019.1 are used to reconstruct the middle ear ossicles, cochlea, and semicircular canals of Stenella from micro CT scans and histological specimens. After reconstruction we use the 3‐D images to evaluate changes in the formation and position of the middle ear ossicles through development.The outline of middle ear and cochlear development in these dolphins is similar to that of land mammals. For example, the otic capsule shows the formation of the cochlea, and ossicle formation passes through mesenchymal and cartilaginous stages. The malleus is attached to Meckel’s cartilage and the stapes is associated with the otic capsule. Additionally, there are general similarities in ossicular shape in the later fetal stages, however in earlier embryonic stages the manubrium of the malleus and the crura of the incus are not as apparent as they are in land mammals, possibly foreshadowing the specific adaptations of cetaceans. Changes within the position of the ossicles in relation to one another as well as the cochlea and semicircular canals occur in order for the middle ear to develop into its adult state. In adult odontocetes, the malleus is fused to the tympanic plate through its anterior process, the process gracilius, creating a folded tympanic membrane. These findings support our hypothesis that many of the middle ear adaptations for odontocetes can be visualized in utero. Preliminary evidence suggests that changes in ossicular position replicate cetacean evolution. This research continues to shed light on how and when these unique changes occur to allow cetacean specialization to underwater hearing.

Phylogenomics of the genus Tursiops and closely related Delphininae reveals extensive reticulation among lineages and provides inference about eco-evolutionary drivers

Phylogeographic inference has provided extensive insight into the relative roles of geographical isolation and ecological processes during evolutionary radiations. However, the importance of cross-lineage admixture in facilitating adaptive radiations is increasingly being recognised, and suggested as a main cause of phylogenetic uncertainty. In this study, we used a double digest RADseq protocol to provide a high resolution (~4 Million bp) nuclear phylogeny of the Delphininae. Phylogenetic resolution of this group has been especially intractable, likely because it has experienced a recent species radiation. We carried out cross-lineage reticulation analyses, and tested for several sources of potential bias in determining phylogenies from genome sampling data. We assessed the divergence time and historical demography of T. truncatus and T. aduncus by sequencing the T. aduncus genome and comparing it with the T. truncatus reference genome. Our results suggest monophyly for the genus Tursiops, with the recently proposed T. australis species falling within the T. aduncus lineage. We also show the presence of extensive cross-lineage gene flow between pelagic and European coastal ecotypes of T. truncatus, as well as in the early stages of diversification between spotted (Stenella frontalis; Stenella attenuata), spinner (Stenella longirostris), striped (Stenella coeruleoalba), common (Delphinus delphis), and Fraser’s (Lagenodelphis hosei) dolphins. Our study suggests that cross-lineage gene flow in this group has been more extensive and complex than previously thought. In the context of biogeography and local habitat dependence, these results improve our understanding of the evolutionary processes determining the history of this lineage.

Leaping small fish out-power breaching whales

When Emmett Johnston from Queen's University, Belfast, UK, attached a motion sensing tag to a basking shark off the Irish coast, he expected the piece of kit to have a sedate ride. Nothing prepared Johnston and colleagues for the rollercoaster that the sensor went on in practice. ‘Having retrieved it, we watched the video and, to our amazement, the movie ended with the shark suddenly accelerating up through the water column, hitting the water surface at 5 m s−1 and breaching for about a second’, says Lewis Halsey from the University of Roehampton, London, UK. The massive fish was behaving more like cavorting gray whales or leaping salmon than the lethargic filter feeder it was meant to be. The team calculated that each leap could use up to 1/17th of the animal's daily metabolic budget (doi:10.1098/rsbl.2018.0537). However, after reviewing movies of breaching basking sharks filmed by observers on land, Halsey suspected that it might be possible to calculate the amount of energy an aquatic animal requires to make it into the air from the footage. ‘I thought there must be lots of video available of other aquatic species breaching’, says Halsey. Could he find a way to calculate how much power it takes for fish, whales and dolphins to surge out of the water from movies shot by citizen scientists?Halsey turned to the millennials’ TV channel of choice. ‘I kept searching YouTube with names of fish and cetaceans and various words for jumping until I couldn't find any more’, he chuckles, recalling how, eventually, he ended up with almost 30 clips of species ranging from a 20 cm long African tetra to a 13 m long humpback whale. Then Halsey teamed up with Gil Iosilevskii from the Technion, Israel, to calculate the animals’ sheer power and speed as they burst out of the water. ‘Gil did the hardcore maths’, recalls Halsey, adding, ‘He is one of the few people around with the capacity to develop the equations we used to estimate power output from the videos’. Halsey then estimated the animals’ sizes, measured the length of time each animal was airborne and determined several other values before plugging them into Iosilevskii's equations.Amazingly, the common bottlenose dolphins and spinner dolphins (both ∼2 m long) hit the highest take-off speeds of ∼10.7 m s−1 (38.5 km h−1), with the smaller species achieving progressively lower speeds; the slowest leaps were performed by the diminutive African tetra, which took off at only 4.4 m s−1. Meanwhile, the largest creatures, including the basking shark, great white shark and massive humpback whale hit speeds ranging from 5.8 to 9.1 m s−1; they didn't come close to challenging the dolphins’ speed. However, when the duo compared the peak muscle power of the animals, it was clear that the smaller species – including mackerel, mullet and the common bottlenose dolphin – generated the highest muscle powers of over 50 W per kg of muscle when jetting out of the waves. In contrast, the heftier great white shark, orca and humpback whale, managed less than 10 W per kg of muscle.Halsey suspects that the smaller species’ powerful departures ‘represents an estimate of a universal upper limit to power output’, adding that their pound-for-pound power was very similar to that of top human athletes performing right at their physical limits. ‘When these animals are breaching at their fastest, they might well be performing at maximum effort’, says Halsey.

A survey of cetaceans found in Mayo Bay, Davao Oriental, Philippines

Cetaceans play an important role in marine ecosystems through the regulation of their prey population. Data on these organisms is scarce because of the difficulties in studying them in the wild. In the Philippines, there is a large gap in knowledge in cetacean research. Short-term studies, including those on strandings, play an important role in addressing the gaps in cetacean research. Boat-based surveys of cetaceans were designed and conducted to create a database of cetaceans in Mayo Bay, Davao Oriental, Philippines. Globicephala macrorhyncus, Peponocephala electra, Stenella attenuata, Stenella longirostris, Tursiops truncatus, and Lagenodelphis hosei cetacean species were encountered during the short-term survey, with Stenella longirostris being the most common cetacean species. Moreover, cetacean strandings within Mayo Bay recorded at least three species that were not observed in the wild during the boat-based survey. This study provided additional information on at least six data-deficient cetacean species of the Philippines and perhaps new information on a species belonging to the genus Mesoplodon in the Philippines, highlighting the importance of Mayo Bay for cetacean research and the need for further investigations in the region.

Real power loss reduction by dolphin swarm algorithm

&lt;p&gt;In this work Spinner Dolphin Swarm Algorithm (SDSA) has been applied to solve the optimal reactive power problem. Dolphins have numerous remarkable natural distinctiveness and living behavior such as echolocation, information interactions, collaboration, and partition of labor. Merging these natural distinctiveness and living behavior with swarm intelligence has been modeled to solve the reactive power problem. Proposed Spinner Dolphin Swarm Algorithm (SDSA) has been tested in standard IEEE 14,300 bus test system and simulation results show the projected algorithm reduced the real power loss extensively.&lt;/p&gt;

New sightings records of marine mammals and seabirds off French Guiana

French Guiana region is one of the most productive in the world and hosts a wide variety of marine vertebrates. In the same time, anthropogenic activities are a growing concern in French Guiana, both in coastal and offshore areas. However, few studies are published on marine mammals, seabirds and potential interactions. Twenty-three marine mammal species are known to occur in the Exclusive Economic Zone (EEZ) and important seabird breeding sites are located in the area. Most of the existing literature relates to breeding birds and coastal cetaceans, but the continental slope appears to be an essential habitat for marine mammals and seabirds. Between October 22 and November 23, 2017, an oceanographic survey was conducted on the Guiana slope to study the quality of sediments and water. Three marine fauna observers (MFOs) were onboard to record sightings of marine mammals and seabirds opportunistically. During 462 h of visual effort in good sighting conditions, 313 sightings (824 individuals) were recorded: 61 marine mammals (501 individuals) and 252 seabirds (323 individuals). Seven seabird families were observed: Laridae (42%), Fregatidae (26%), Procellariidae (12%), Stercorariidae (10%), Hydrobatidae (4%), Sulidae (2%) and Phaethontidae (1%). 3% concerned wader species. The most frequently observed seabird species was the magnificent frigatebird ( Fregata magnificens ), as well as the common tern ( Sterna hirundo ), Cory’s shearwater ( Calonectris diomedea ) and the pomarine jaeger ( Stercorarius pomarinus ). Many Delphinidae species were observed ( Stenella longirostris , Stenella attenuata , Stenella frontalis , Delphinus delphis , Tursiops truncatus ) in addition to sperm whales ( Physeter macrocephalus ) and humpback whales ( Megaptera novaeangliae ). Only a few sightings of humpback whales have been previously recorded in this area. Sighted individuals were mainly mother-calf pairs suggesting that the area may be an extended part of a calving ground for humpback whales.

Population ecology and the management of whale watching operations on a data-deficient dolphin population.

Whale watching is a popular commercial activity, producing socio‐ecological benefits but also potential long‐term effects on the targeted cetacean population. This industry is currently developing in data‐deficient contexts in a largely unregulated fashion. Management schemes should adopt precaution and be informed by the relevant literature, but would be more effective if the assessment of the target population vulnerability, biological impacts, and management implications was drawn from site‐specific data.This paper focuses on a reef‐associated, data‐deficient population of spinner dolphins in the Egyptian Red Sea. In Satayah Reef, new information on population size and dynamic parameters were documented using visual observation and photo‐identification‐based capture–recapture methods (Cormack–Jolly–Seber time‐since‐marking model).Dolphins occurred on 98% of the survey days. Average school size was 66 individuals (±42.1 SE), with most groups including calves. The population was equally divided into recurrent and transient individuals. An “emigration + mortality” model best described residence at the site. Five recurrent males (5% of the Satayah population) provided connectivity between this and the geographically close population of Samadai Reef.Average annual survival probability was 0.83 (±0.06 SE) in the year following first capture and 0.99 (±0.06 SE) for recurrent individuals. Mean yearly population sizes ranged 143–207 individuals.The study had the power to detect a 30% decline in the population, but not the rate of change in abundance estimated from the data (r = 0.018 ± 0.04), which would have required a 3‐ to 5‐times longer study. Synthesis and application: These findings advance the assessment of the Satayah population's intrinsic vulnerability and have three major management applications: (a) the delineation of management units; (b) the identification of key indicators for future impact monitoring and assessment; and (c) realistic estimates of the statistical power for trend detection. Based on our results, we recommend supporting future research, devising site‐specific time–area closure plans, and integrating them in a regional scheme. Approaches employed in this case study can inform the management of whale watching industries targeting other data‐deficient populations.

Transmission beam pattern and dynamics of a spinner dolphin (Stenella longirostris).

Toothed whales possess a sophisticated biosonar system by which ultrasonic clicks are projected in a highly directional transmission beam. Beam directivity is an important biosonar characteristic that reduces acoustic clutter and increases the acoustic detection range. This study measured click characteristics and the transmission beam pattern from a small odontocete, the spinner dolphin (Stenella longirostis). A formerly stranded individual was rehabilitated and trained to station underwater in front of a 16-element hydrophone array. On-axis clicks showed a mean duration of 20.1 μs, with mean peak and centroid frequencies of 58 and 64 kHz [standard deviation (s.d.) ±30 and ±12 kHz], respectively. Clicks were projected in an oval, vertically compressed beam, with mean vertical and horizontal beamwidths of 14.5° (s.d. ± 3.9) and 16.3° (s.d. ± 4.6), respectively. Directivity indices ranged from 14.9 to 27.4 dB, with a mean of 21.7 dB, although this likely represents a broader beam than what is normally produced by wild individuals. A click subset with characteristics more similar to those described for wild individuals exhibited a mean directivity index of 23.3 dB. Although one of the broadest transmission beams described for a dolphin, it is similar to other small bodied odontocetes.

Molecular, serological, pathological, immunohistochemical and microbiological investigation of Brucella spp. in marine mammals of Brazil reveals new cetacean hosts.

Brucella-exposure and infection is increasingly recognized in marine mammals worldwide. To better understand the epidemiology and health impacts of Brucella spp. in marine mammals of Brazil, molecular (conventional PCR and/or real-time PCR), serological (Rose Bengal Test [RBT], Competitive [c]ELISA, Serum Agglutination Test [SAT]), pathological, immunohistochemical (IHC) and/or microbiological investigations were conducted in samples of 129 stranded or by-caught marine mammals (orders Cetartiodactyla [n=124], Carnivora [n=4] and Sirenia [n=1]). Previous serological tests performed on available sera of 27 of the 129 animals (26 cetaceans and one manatee), indicated 10 seropositive cetaceans. Conventional PCR and/or real-time PCR performed in cases with available organs (n=119) and/or blood or swabs (n=10) revealed 4/129 (3.1%) Brucella-infected cetaceans (one of them with positive serology; the remaining three with no available sera). Pathological, IHC and/or microbiological analyses conducted in PCR/real-time PCR and/or seropositive cases (n=13) revealed Brucella-type lesions, including meningitis/meningoencephalitis, pneumonia, necrotizing hepatitis, pericarditis and osteoarthritis in some of those animals, and positive IHC was found in all of them (excepting two live-stranded animals without available organs). Brucella spp. culture attempts were unsuccessful. Our results demonstrated exposure, asymptomatic, acute and chronic Brucella sp. infection in several cetacean species in the Brazilian coast, highlighting the role of this pathogen in stranding and/or death, particularly in Clymene dolphin (Stenella clymene) and short-finned pilot whale (Globicephala macrorhynchus) off Ceará State. Novel hosts susceptible to Brucella included the franciscana (Pontoporia blainvillei), the Guiana dolphin (Sotalia guianensis) and the spinner dolphin (Stenella longirostris). Additionally, three coinfection cases involving Brucella spp. and cetacean morbillivirus, Edwarsiella tarda and Proteus mirabilis were detected. To the best of our knowledge, this is the first long-term and large-scale survey of Brucella spp. in marine mammals of South America, widening the spectrum of susceptible hosts and geographical distribution range of this agent with zoonotic potential.

Ecological Niche Modeling of Three Species of Stenella Dolphins in the Caribbean Basin, With Application to the Seaflower Biosphere Reserve

Dolphins of the genus Stenella occur in pelagic waters of both tropical and warm-temperate oceans. Three species, the Atlantic spotted dolphin (Stenella frontalis), the pantropical spotted dolphin (S. attenuata), and the spinner dolphin (S. longirostris) are abundant worldwide, but in the Caribbean Basin they have been poorly studied and information on their distribution patterns is scarce. Specifically, in Colombia’s remote Seaflower Biosphere Reserve (SFBR) S. attenuata has been reported occasionally, but S. frontalis and S. longirostris have never been recorded before. To address this information gap, an ecological niche modeling approach was used to determine the potential distribution patterns of these three dolphin species in the region. Records of these species for the Caribbean Basin were compiled, including both published and unpublished data. Environmental information, including bathymetry, bathymetric slope, distance to shore, sea surface temperature, sea surface salinity, and chlorophyll-a concentration was gathered from public databases (MARSPEC and Bio-ORACLE) in raster format. The maximum entropy algorithm (Maxent) for modeling species’ geographic distributions with presence-only data was used. After filtering the data, 210 records of S. attenuata, 204 of S. frontalis, and 80 of S. longirostris were used to run models. The best configuration for each model was chosen based on the ΔAICc criterion. For all three species, the final ecological niche models returned AUC test values higher than 0.8, indicating satisfactory model performance. The resulting potential distribution maps suggested that areas closest to continental shorelines of the Caribbean Basin and surrounding islands had the highest environmental suitability for all species (>70%). All models reported high environmental suitability for S. attenuata and S. longirostris in the SFBR, mainly in the southernmost part surrounding San Andres and Providence Archipelago. Assessment of niche overlap from the predictions of species distributions using the similarity statistic and pairwise map overlap indicated that S. frontalis and S. longirostris had niches slightly more similar in comparison to S. attenuata. As this was a first effort to fill a gap in our understanding of the distribution of species in the genus Stenella in the Caribbean Basin, further studies are necessary using both niche modeling and biological/ecological approaches.

Observations of cetaceans off southern Sri Lanka, April 2007–2013

Cetaceans were observed off the South coast of Sri Lanka in the month of April, every year over a seven-year period, 2007–13. During 48 days atsea a total of 290 cetacean sightings were recorded. Blue whales were abundant, accounting for 61% (n = 177) of all sightings. This concentrationof blue whales was predicted and discovered based on a migration hypothesis and there was evidence of the expected net westward movement inApril. Nevertheless, most blue whales seen were not obviously on passage and many appeared to be feeding. Mothers with calves and likelyreproductive behaviour (breaching and rushing) were also observed. There were five sightings of Bryde’s-type whales (B. brydei/edeni); four wereidentified as B. brydei, one was identified as B. edeni. Sperm whales were sighted 16 times within a narrow band centred just outside the 1,000misobath. Modal group size was 10–12; based on size most individuals appeared to be mature females or immatures. Spinner dolphin (n = 35 sightings)was the most abundant species, accounting for 67% of all cetaceans seen by number of individuals. They were frequently associated with tuna andseabirds. Risso’s dolphin was only seen once, despite being reported as common around Sri Lanka in the early 1980s. They were taken in largenumbers by local fisheries, which may have reduced local abundance. Other species recorded were: dwarf sperm whale (n = 3 sightings); shortfinnedpilot whale (n = 3); common bottlenose dolphin (n = 9); Indo-Pacific bottlenose dolphin (n = 3); pantropical spotted dolphin (n = 4); andstriped dolphin (n = 4). Since the discovery of blue whales off southern Sri Lanka, commercial whale watching centred on the fishing port of Mirissahas developed rapidly, bringing new revenue to the region but also the potential for disturbance to the whales.

Seasonal and interannual variations in the distributions of tuna-associated dolphins in the eastern tropical Pacific Ocean

Seasonal and interannual (El Niño–La Niña) variations in dolphin distributions in the eastern tropical Pacific Ocean have not been quantified, inspite of an extensive research vessel database. Fisheries observer data from the yellowfin tuna purse-seine fishery, collected year-round from 1986through 2015, were used to construct a binned spatiotemporal dataset of the presence/absence of spotted, spinner and common dolphin schools bymonth and 1° area. Distribution patterns were predicted from generalised additive logistic regression models applied to the binned data, with dynamicpredictors of surface temperature and salinity, thermocline depth and a stratification index. The dolphin taxa, especially common dolphins, showsome niche separation in relation to these variables. Predicted distributions for each taxon showed seasonal and interannual differences. Spottedand spinner dolphins responded to changes in the position and size of the eastern Pacific warm pool and avoided the equatorial cold tongue inSeptember–October and during La Niña. Common dolphins responded to seasonal and interannual changes in the Costa Rica Dome, the cold tongue,and the coastal upwelling habitat along Baja California, Peru and Ecuador. These predicted temporal variations are consistent with changes inpreferred habitat driven by environmental variability.

Reproduction and morphology of Central American and Tres Marias spinner dolphins in the eastern tropical Pacific

AbstractFour geographic forms of spinner dolphin (Stenella longirostris) occur in the eastern tropical Pacific. Two of the forms are pelagic: the eastern and whitebelly, and two are coastal: the Central American and Tres Marias spinner dolphins. Of these, only the Tres Marias form lacks recognition appropriate for developing management and conservation plans. Vertical aerial photographs of 57 spinner dolphin schools taken between 1988 and 2006 were used to examine the range of coastal forms and to characterize their calving seasons. On the basis of adult body length, spinner dolphins photographed off Guerrero, Mexico, were identified as those of the Central American form, which is north of their known range, and those photographed farther north, approximately 112 km off Nayarit, Mexico, were identified as the Tres Marias form. Calving peaked from October through March, and there was evidence that calving seasons differed among geographic forms with coastal forms calving later than pelagic forms. We present the first life history parameter estimates for the coastal forms of spinner dolphins, provide additional support for recognition of the Tres Marias form, and the first evidence of the Central American form occurring north of the Gulf of Tehuantepec, Mexico.

Mitogenomic differentiation in spinner (Stenella longirostris) and pantropical spotted dolphins (S. attenuata) from the eastern tropical Pacific Ocean

AbstractSpinner dolphins (Stenella longirostris) and pantropical spotted dolphins (S. attenuata) show high intraspecific morphological diversity and endemic subspecies in the eastern tropical Pacific Ocean (ETP). Previous studies of mitochondrial DNA have found low genetic differentiation among most of these groups, possibly due to demographic factors, ongoing gene flow, and/or recent divergence. These species were heavily depleted due to bycatch in the ETP yellowfin tuna fishery. Because understanding population structure is important for accurate management of the recovery of these species, we collected whole mitochondrial genome sequences from 104 spinner and 76 spotted dolphins to test structure hypotheses at multiple hierarchical taxonomic levels. Results show differences between subspecies of spinner and spotted dolphins, but no support for the division of existing offshore stocks of spotted dolphins. We compare these results to previous results of genome‐wide nuclear SNP data and suggest high haplotype diversity, female dispersal, and/or relative power of the two data sets explains the differences observed. Interestingly, increasing the amount of mitochondrial data (base pairs and genes) did not increase ability to delimit population units. This study supports a genetic basis for management units at the subspecies level, and provides critical information for mitigating historical and continued fisheries impacts.