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Summary Cetaceans are the only mammals to have evolved hyperphalangy, an increase in the number of phalanges beyond the mammalian plesiomorphic condition of three phalanges per digit. In this study, cetaceans were used as a novel model to review previous studies of mammalian hyperphalangy and contribute new experimental evidence as to the molecular origins of this phenotype in embryos of the pantropical spotted dolphin (Stenella attenuata). Results show embryos of dolphins, mice, and pigs share similar spatiotemporal patterns of signaling proteins known to shape limbs of mammals (e.g., FGF8, BMP2/4, WNT, GREM). However, fetal dolphins differ in that their interdigital tissues are retained, instead of undergoing apoptosis, and that multiple waves of interdigital signals likely contribute to the patterning of supernumerary joints and phalanges in adjacent digits. Integration of fossil and experimental evidence suggests that the presence of interdigital webbing within the fossils of semi-aquatic cetaceans, recovered from the Eocene Epoch (49Ma), was probably the result of BMP-antagonists counteracting interdigital apoptosis during embryonic limb development. Modifications to signals originating in these interdigital tissues likely contributed to the origin of an incipient form of hyperphalangy in obligatorily aquatic cetaceans about 35Ma. Finally, an extreme form of hyperphalangy, with six or more phalanges per digit, evolved independently in rorqual whales (Balaenopteridae) and delphinids, and was probably associated with a wave of signaling within the interdigital tissues.

The northeastern offshore population of the pantropical spotted dolphin (Stenella attenuata) in the east- ern tropical Pacific remains listed as depleted under the Marine Mammal Protection act, and recent estimates of abundance show that recovery has been slow. One hypoth- esis for the slow recovery is that continued chase and encir - clement by the tuna fishery negatively affects reproduction. Insufficient life-history sampling in this region over the last two decades makes traditional estimates of reproductive rates impossible. Here, we examine the current reproduc- tive patterns of these dolphins by measuring blubber pro- gesterone (BP) concentrations in biopsy samples to assess pregnancy state. BP was quantified in 212 biopsies from female offshore spotted dolphins sampled between 1998 and 2003 in the northeastern tropical Pacific, and we found that 11.5 % of the biopsied females (mature and immature) were pregnant. The relationship between pregnancy and fishery exposure was analyzed, and we found that pregnant females were exposed to significantly less fishery activ- ity than non-pregnant ones (p = 0.022), suggesting that the fishery may have an inhibitive effect on pregnancy. Spatial analysis indicated that pregnancy was more aggre- gated than random (p < 0.05) at a scale up to 180-nmi, with

Millions of spinner (Stenella longirostris) and pantropical spotted dolphins (Stenella attenuata) died since the 1960's as bycatch in tuna nets in the eastern tropical Pacific Ocean. Despite three decades of protection, they show little-to-no sign of recovery (although recent fisheries-independent abundance estimates are not available). In efforts to establish biologically meaningful management boundaries for recovery, endemic subspecies and multiple stocks have been proposed. However, genetic differentiation among most of these units has been difficult to identify, possibly due to low statistical power stemming from large historical abundances, ongoing gene flow, and recent divergence. We tested for genetic structure at multiple hierarchical levels by analyzing the largest dataset to date brought to bear on these questions. Single nucleotide polymorphisms (SNPs) were collected from nuclear DNA regions associated with the restriction enzyme site PstI from 72 spinner dolphins and 58 pantropical spotted dolphins using genotype-by-sequencing (GBS). Our results support the current subspecies for both species and indicate stock-level separation for Tres Marias spinner dolphins and the two offshore pantropical spotted dolphin stocks in this area. Although bycatch has been reduced to a small fraction of pre-protection levels, incidental mortality continues to impact these populations. Our results are important for the ongoing management and recovery of these highly-impacted pelagic dolphins in the eastern tropical Pacific Ocean.

Spinner dolphins (Stenella longirostris) and spotted dolphins (S. attenuata) show high intraspecific morphological diversity and endemic subspecies in the eastern tropical Pacific Ocean (ETP). Previous studies of mitochondrial DNA (mtDNA) 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 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 levels. Our results showed significant differences between subspecies of spotted (FST: 0.0125;P =0.0402) and spinner dolphins (FST: 0.0133;P= 0.034), but no support for the division of existing offshore stocks of spotted dolphins or Tres Marias spinner dolphins. We compare these results to previous results of genome-wide nuclear SNP data and suggest high haplotype diversity, female dispersal, male philopatry, or relative power of the two datasets explains the differences observed. Our results further support a genetic basis for biologically meaningful management units at the subspecies level, and provide a critical component to mitigating historical and continued fishery interactions.

Funding for HARP data collection and analysis was provided by the Natural Resource Damage Assessment partners (20105138) and the Center for the Integrated Modeling and Analysis of the Gulf Ecosystem (C-IMAGE) Consortium of the BP/Gulf of Mexico Research Initiative (SA 12-10/GoMRI-007). The analyses and opinions expressed are those of the authors and not necessarily those of the funding entities. This research was made possible by a grant from The Gulf of Mexico Research Initiative/C-IMAGE II. The probability of detecting echolocating delphinids on a near-seafloor sensor was estimated using two Monte Carlo simulation methods. One method estimated the probability of detecting a single click (cue counting); the other estimated the probability of detecting a group of delphinids (group counting). Echolocation click beam pattern and source level assumptions strongly influenced detectability predictions by the cue counting model. Group detectability was also influenced by assumptions about group behaviors. Model results were compared to in situ recordings of encounters with Risso's dolphin (Grampus griseus) and presumed pantropical spotted dolphin (Stenella attenuata) from a near-seafloor four-channel tracking sensor deployed in the Gulf of Mexico (25.537°N 84.632°W, depth 1220 m). Horizontal detection range, received level and estimated source level distributions from localized encounters were compared with the model predictions. Agreement between in situ results and model predictions suggests that simulations can be used to estimate detection probabilities when direct distance estimation is not available. Publisher PDF

Funding to support P.L.T. was received from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. This study characterizes daytime acoustic and dive behavior of pantropical spotted dolphins (Stenella attenuata) in Hawai‘i using 14.58 h of data collected from five deployments of digital acoustic recording tags (DTAG3) in 2013. For each tagged animal, the number of whistles, foraging buzzes, dive profiles, and dive statistics were calculated. Start, end, minimum, and maximum frequencies, number of inflection points and duration were measured from 746 whistles. Whistles ranged in frequency from 9.7 ± 2.8 to 19.8 ± 4.2 kHz, had a mean duration of 0.7 ± 0.5 s and a mean of 1.2 ± 1.2 inflection points. Thirteen foraging buzzes were recorded across all tags. Mean dive depth and duration were 16 ± 9 m and 1.9 ± 1.0 min, respectively. Tagged animals spent the majority of time in the upper 10 m (76.9% ± 16.1%) of the water column. Both whistle frequency characteristics and dive statistics measured here were similar to previously reported values for spotted dolphins in Hawai‘i. Shallow, short dive profiles combined with few foraging buzzes provide evidence that little spotted dolphin feeding behavior occurs during daytime hours. This work represents one of the first successful DTAG3 studies of small pelagic delphinids, providing rare insights into baseline bioacoustics and dive behavior. Publisher PDF

Hematology, serum chemistry, and plasma hormones were evaluated in 72 pantropical spotted dolphins (Stenella attenuata attenuata) from the eastern tropical Pacific in an attempt to define the degree of stress associated with chase and encirclement by a tuna purse seiner, and are here reported for the first time for this species. Dolphins had high levels of dopamine and moderately elevated levels of enzymes indicative of the expected muscle damage following exertion of the chase. The length of time between the start of the capture operation and blood sampling correlated with increases in platelet and white blood cell counts and mean cell hemoglobin concentration, while the length of time between net tie-down and blood sampling influenced platelet, white blood cell, and eosinophil counts. Ten dolphins recaptured 1–3 d after their first capture had significantly lower serum creatinine kinase, thyroid (T4) and globulin levels compared to values in dolphins sampled at nominal first capture. Although small sample sizes and large individual variation limit interpretation, these data indicate a stress response occurred in all dolphins, but the extent of the response is within the expected range for adaptive responses previously measured in limited numbers of wild mammals.

Mixed-species associations are temporary aggregations of individuals of different species involved in similar activities. Such associations form for foraging, protection against predators, and social advantage. Mixedspecies groups in delphinids are frequent in the wild. We aimed to understand the ecological significance of mixed-species group formation by 2 tropical delphinids, the spinner dolphin (Stenella longirostris) and the pantropical spotted dolphin (Stenella attenuata), in waters surrounding the island of Mayotte in the southwestern Indian Ocean. We used sighting data collected year-round from 2004 to 2009. We encountered a total of 67 mixed-species groups (comprising 21% of all groups observed) of spinner and pantropical spotted dolphins around Mayotte. No daily or seasonal variability in the occurrence of associations was detected. Behavioral activities of single- and mixed-species groups differed significantly. Foraging was observed only in single-species groups of pantropical spotted dolphins. Mixed-species groups were larger than single-species groups. When in association, spinner dolphins used deeper waters than while in single-species groups. No evidence of association for social advantage was observed. We suggest that spinner dolphins associate with spotted dolphins for protection against predators when transiting between resting areas.

International audience; Investigating ecological segregation among organisms of a given community is challenging, especially when these organisms share similar patterns of distribution, and similar size and morphology. Around the island of Mayotte, a diversified community of at least four sympatric delphinids is present year round within a very restricted range: the Indo-Pacific bottlenose dolphin (Tursiops aduncus), the spinner dolphin (Stenella longirostris), the pantropical spotted dolphin (Stenella attenuata), and the melon-headed whale (Peponocephala electra). In addition, the Fraser's dolphin (Lagenodelphis hosei) makes temporary incursions into peri-insular waters as well. This study aims to assess niche segregation among this tropical dolphin community. We hypothesized that each species occupies its own distinct niche, defined by the following axes: habitat, resources and time. We analysed habitat in relation to physiography, behavioural budgets and C and N stable isotope values from skin and blubber samples for each species. The results highlighted that habitat and behavioural budgets were relatively distinct among species, with few exceptions. However, in those species living on the outer reef slope where habitat and behaviour were not well discriminated, stable isotope analyses confirmed that species have different trophic levels (mostly reflected through δ15N values) and/or foraging habitat (mostly reflected through δ13C values). This study confirms that the use of multiple methodologies (habitat, behaviour and feeding ecology studies) help in discerning ecological niche segregation, especially when examining closely related species within a common restricted range.

Food is one of the most important dimensions of resource partitioning for species coexistence. In this study, we investigated the dietary composition and foraging habits of three sympatric odontocetes in order to identify their levels of food niche overlap and ecological separation. Stomach content analysis was performed on samples collected from carcasses confiscated by police or entangled in gill nets from 1994 to 2001, including 27 Risso's dolphins (GG) (Grampus griseus), 27 Fraser's dolphins (LH) (Lagenodelphis hosei), and 45 pantropical spotted dolphins (SA) (Stenella attenuata). GG consumed only cephalopods, with Enoploteuthis chunii accounting for 90.5% of total prey consumed, LH fed on mesopelagic fishes and cephalopods, dominated by hatchetfish, Polyipnus stereope (50.2%), and SA ate both mesopelagic and epipelagic preys, primarily fishes of Myctophum asperum (20.3%) and squids of E. chunii (25.8%). Among the three odontocetes, GG had the narrowest dietary niche width, while SA had the widest width. Both the niche overlap index and the analysis of similarities (ANOSIM) showed significant diet differentiation among these three dolphin species. The depth distribution of their principal prey items further suggests that LH feeds in the deepest waters while SA utilizes prey resources near surface.

Cetacean distribution and abundance are reported from the first systematic line-transect visual survey in the waters of Guam and the Commonwealth of the Northern Mariana Islands (CNMI). The survey was conducted during January–April 2007 following standard line-transect protocols. Trackline coverage (11,033 km) was dominated by high sea states (88.2%); however, 13 cetacean species were recorded. The sperm whale (Physeter macrocephalus) was the most frequently encountered whale, followed by Bryde's and sei whales (Balaenoptera edeni and B. borealis, respectively). Occurrence of the sei whale is unique, because the species had not been confirmed to occur south of 20° N. The pantropical spotted dolphin (Stenella attenuata) was the most frequently sighted delphinid, followed by the striped dolphin (Stenella coeruleoalba) and false killer whale (Pseudorca crassidens). Humpback whales (Megaptera novaeangliae) were acoustically detected and later seen off Saipan. Numerous cetacean sightings were associa...

Unlike other mammals, odontocetes and mysticetes have highly derived craniofacial bones. A growth process referred to as "telescoping" is partly responsible for this morphology. Here, we explore how changes in facial morphology during fetal growth relate to differences in telescoping between the adult odontocete Stenella attenuata and the mysticete Balaena mysticetus. We conclude that in both Stenella and Balaena head size increases allometrically. Similarly, odontocete nasal length and mysticete mouth size have strong positive allometry compared to total body length. However, the differences between odontocetes and mysticetes in telescoping are not directly associated with their fetal growth patterns. Our results suggest that cranial changes related to echolocation and feeding between odontocetes and mysticetes, respectively, begin during ontogeny before telescoping is initiated.

Cetacean diversity and occurrence has never been investigated in the Union of the Comoros, located in the northern Mozambique Channel. Small boat-based surveys were conducted during the austral winter of 2002, primarily to assess the occurrence of humpback whales (Megaptera novaeangliae) and whether the area represents a wintering ground where the species reproduce. All other cetacean species were also recorded. Opportunistic sighting records were used to provide information on the diversity of cetaceans occurring in the area. Between 2000 and 2003, 12 cetacean species were recorded around the Comoros, including: Megaptera novaeangliae, Stenella longirostris, Peponocephala electra, Stenella attenuata, Tursiops truncatus, Globicephala macrorhynchus, Mesoplodon densirostris, Physeter macrocephalus, Lagenodelphis hosei, Grampus griseus, Mesoplodon pacificus and possibly Tursiops aduncus. During the dedicated surveys, the humpback whale was the most commonly encountered species (72% of sightings) followed by the spinner dolphin (15%). Humpback whale group composition was heterogeneous, but mother-calf pairs were the most commonly sighted (49%). This study demonstrates that the Union of the Comoros is an important site for migrating humpback whales in the southwest Indian Ocean and for a wide variety of toothed cetacean species.

The large majority of cetacean interspecific studies report only on dolphin interactions, while studies on interactions between odontocete and mysticete are less common. The present work aims to report on sightings of cetacean interactions, during the breeding season of humpback whales(Megaptera novaeangliae), along 370 km of the Bahia State, north-eastern Brazil, addressing aspects of cetacean distribution and behaviour. During 7 seasons (2000–2006), a total of 230 research cruises were performed, in which 38 events of interactions among humpback whales and other cetaceans(Tursiops truncatus, Steno bredanensis, Peponocephala electraandBalaenoptera acutorostrata)were observed, plus another 5 encounters without the whale's presence, includingT. truncatus, S. bredanensis, P. electra, Stenella clymeneandStenella attenuata. Our results confirm the occurrence of multiple cetacean species in the Bahia State, being the first study in the world to report on a large range of interactions involving another 4 cetacean species, grouped with up to 3 mixed species per sighting, with humpback whales in their annual breeding ground.

We radio tracked 20 pantropical spotted dolphins (Stenella attenuata )i n the pelagic waters of the eastern tropical Pacific Ocean during three research cruises in 1992, 1993, and 2001. Dolphins were tracked for up to 6 d from 20 to 1,000 km offshore. Seventeen of these dolphins also carried time–depth recorders, nine of which were recovered with a combined total of 477 h of dive data. The movement data suggested that the dolphins associate with areas of relatively high biological productivity. Dolphins close to shore moved along the continental slope, while some dolphins traveled farther offshore along thermocline “ridges.” Tracking and tagging multiple dolphins demonstrated the dynamic nature of dolphin herds, which change size and membership over the course of a day. At night, the dolphins traveled more slowly but dove deeper and longer, with more rapid ascents and descents than during daylight hours. These nighttime dive characteristics support the hypothesis suggested by some food habit studies that spotted dolphins are nocturnal feeders. Comparison of dive data with acoustic backscatter data indicates that spotted dolphins typically begin and end nighttime feeding activities with dusk and dawn diving bouts that track the vertical migration of organisms associated with the deep scattering layer.

Cranial variation in 129 pantropical spotted dolphins (Stenella attenuata) from the western and eastern tropical Pacific was investigated morphometrically. This study revealed significant sexual dimorphism in the dolphin skulls. Differences between the genders were mostly recorded in the rostrum and braincase, which are wider and more robust in males. This sexual variation was interpreted in terms of differences in behavioral and life-history strategies between genders. Geographical variation among populations of the eastern tropical Pacific (ETP), Japan, and Taiwan was also significant, with different sexual patterns. While no clear trend in geographical variation was detected in males, there was a positive relationship in females between morphological differences and geographical distance. That is, Japanese and Taiwanese female specimens were morphologically more similar than revealed by other pairwise comparisons between them and the ETP specimens. Moreover, two canonical discriminant functions further discriminated the three populations for males and females, respectively. The two functions showed that the rostrum and braincase are the principal elements in discrimination of geographical variation in males, while only the rostrum is the major discriminant morph of geographical variation in females. In addition, tests based on Mahalanobis distance-squares were conducted to assign six specimens from the western tropical Pacific to the above three populations to clarify the similarities among them.

Reproductive data for 2 pelagic dolphin subspecies in the eastern tropical Pacific, the eastern spinner (ES) dolphin Stenella longirostris orientalis and northeastern pantropical spotted (NEPS) dolphin S. attenuata attenuata, were obtained from aerial photographs taken between 1987 and 2003. Two measures of reproductive output were estimated: proportion of adult dolphins with calves ('proportion with calves') and length at which calves disassociated from their mothers ('length at disassociation'). Trends in length at disassociation were investigated to determine if the proportion with calves was affected by possible changes in calving interval, but no changes were found. Propor- tion with calves for ES dolphins was stable from 1987 to 1993, then declined from 1993 to 2003; pro- portion with calves for NEPS dolphins decreased steadily from 1987 to 2003. For both species, propor- tion with calves was related to number of dolphins in the school of the focal species and/or proportion of the school made up of the focal species. For NEPS dolphins, annual number of purse-seine sets on dolphins was a predictor of both proportion with calves and length at disassociation. Because NEPS dolphins are the main species targeted by the fishery, the link between fishing activity and both mea- sures of reproductive output indicates that the fishery has population-level effects beyond reported direct kill. Decline in reproductive output is the proximate cause or one of the proximate causes of the failure of dolphin populations to recover at rates expected after reduction of high bycatch levels.

This work compiles a decade (2001-2010) of marine mammal sightings in the Malpelo Fauna and Flora Sanctuary (FFS) and the area between the island and mainland coast. Four separate sources of data were consulted, which used visual searching during cruising efforts while Malpelo’s surrounding waters were surveyed from a vantage point. Seven species were identified in the FFS: October and November were the months with higher species richness. Tursiops truncatus had the highest encounter rates (17.78 groups/100 h), followed by Megaptera novaeangliae (1.62) and Stenella attenuata (0.88). These species were usually within 6 km from the island. Other species seen around the island include Stenella coeruleoalba, Delphinus delphis, Stenella longirostris and Zalophus wollebaeki. On the other hand, thirteen species were identified during cruises, and March and April were the months with the highest species richness. Megaptera novaeangliae had the highest encounter rate (5.94), followed by T. truncatus (3.30), S. attenuata (3.08), D. delphis (3.08) and S. coeruleoalba, Globicephala macrorhynchus and Orcinus orca, each one with 0.66. Other species seen during the cruises include Steno bredanensis, Pseudorca crassidens, Grampus griseus, Peponocephala electra, Physeter macrocephalus and Ziphius cavirostris. Megaptera novaeangliae were associated to the continental shelf, T. trunctaus and D. delphis to oceanic waters, and S. attenuata to both the continental shelf and oceanic waters. Delphinus delphis was more abundant in intermediate waters, during the first trimester (January-March), while T. truncatus was the most abundant species around the Sanctuary during all seasons, suggesting that is the same population. The latter was also the only species found all year round in both zones (around the island and in oceanic waters), and encounter rates did not change across years. Megaptera novaeangliae had a seasonal presence (mostly June to November) with a higher abundance during the third trimester (July-September), both around Malpelo and the transect. The presence of humpback whales calves suggests that Malpelo is used for reproductive purposes. This new information about the marine mammals found in Malpelo FFS and the area between the island and the continent contributes to the understanding of these species in Colombian waters.

We assess the status of 2 dolphin stocks affected by purse-seine fishing in the eastern topical Pacific and evaluate hypotheses for their lack of re- covery. We use Bayesian methods and fit generalized models of logistic population growth to abundance estimates for northeastern offshore spotted dolphins Stenella attenuata attenuata and eastern spinner dol- phins Stenella longirostris orientalis. In 2002, using the definition of depletion stipulated in the USA Marine Mammal Protection Act, northeastern offshore spotted dolphins were almost certainly 'depleted'. There is, however, uncertainty in the degree to which the stock was depleted. Eastern spinner dolphins were most likely depleted in 2002, but there is a small probability that this was not the case. Uncertainty in the degree to which both stocks were depleted stems from uncertain- ties in maximum net productivity levels and carrying capacities. Based on abundance data from 1979 to 2000, both stocks were estimated to have had maximum growth rates of 77% probability, lower than the accepted minimum default value for dolphin populations with reproductive parameters (e.g. calving intervals) like those considered here (Reilly & Barlow 1986, Fish Bull 84:527-533; Wade 1998, Mar Mamm Sci 14:1-37). We fit models that are intended to be indica- tive of hypotheses that explain why neither dolphin stock has recovered. Our data and prior information provide equal posterior support to hypotheses which at- tribute the lack of recovery to the fishery and changes in the ecosystem. We conclude that (1) the purse-seine fishery can impact dolphin stocks beyond the impacts of observed fishery mortality, (2) there is uncertainty about the degrees to which such cryptic impacts have population-level consequences, and (3) the existing dolphin-safe labeling standard is, from a conservation perspective, robust to this uncertainty.

To enhance our understanding of how aquatic endotherms respond thermally to their environment, we present two new designs for recording heat flux (HF) and skin temperature (Ts) from the dorsal fins of free-ranging dolphins. The first package, held on by a series of small suction cups, was designed for short-term deployments on the order of hours. The second package, a long-term attachment, was held on via two 5.0-mm -Delrin® pins and was designed for deployments on the order of days. The former version was configured to release remotely, by way of a galvanic linkage, removing the need to re-capture tagged dolphins. The latter was designed to be removed after re-capture of the individual but also included a fail–safe galvanic release. One of the major advances of our approach is that it allows both convective and conductive pathways of heat loss to be dynamically recorded from freeswimming wild dolphins, whereas previous approaches have recorded primarily conductive heat loss from trained captive or restrained wild dolphins. The short-term, re-usable package has been field-tested on 55 bottlenose dolphins (Tursiops truncatus )i n Sarasota Bay, Florida and the long-term device on two spotted dolphins (Stenella attenuata) in the eastern tropical Pacific Ocean. By also incorporating into each package a time–depth–velocity recorder we were able to examine patterns of heat flux in relation to changing behavioural states of the tagged individual. Heat flux recorded at the dorsal fin was found to be individually variable and dynamic. Water temperature (Tw) had a profound effect on patterns of heat loss in both species with HF increasing with even minor decreases in Tw. This device significantly improves our ability to understand the thermal biology of dolphins as they move about in their natural environment. © 2007 Published by Elsevier B.V.

The ability to identify delphinid vocalizations to species in real-time would be an asset during shipboard surveys. An automated system, Real-time Odontocete Call Classification Algorithm (ROCCA), is being developed to allow real-time acoustic species identification in the field. This Matlab-based tool automatically extracts ten variables (beginning, end, minimum and maximum frequencies, duration, slope of the beginning and end sweep, number of inflection points, number of steps, and presence/absence of harmonics) from whistles selected from a real-time scrolling spectrograph (ISHMAEL). It uses classification and regression tree analysis (CART) and discriminant function analysis (DFA) to identify whistles to species. Schools are classified based on running tallies of individual whistle classifications. Overall, 46% of schools were correctly classified for seven species and one genus (Tursiops truncatus, Stenella attenuata, S. longirostris, S. coeruleoalba, Steno bredanensis, Delphinus species, Pseudorca crassidens, and Globicephala macrorhynchus), with correct classification as high as 80% for some species. If classification success can be increased, this tool will provide a method for identifying schools that are difficult to approach and observe, will allow species distribution data to be collected when visual efforts are compromised, and will reduce the time necessary for post-cruise data analysis.

The occurrence, distribution and structure of cetacean communities in the tropical South Atlantic beyond the shelf edge are poorly known with little dedicated research occurring within this region. At 15°58′S 005°43′W, the island of St Helena is one of the few areas of land within this region and the only one that lies in the tropical south-eastern Atlantic. As a result, St Helena offers a unique opportunity to study cetaceans within this area using small boats and land-based observations. This paper describes the results of a preliminary, short-term survey of the cetacean community around St Helena in the austral winter of 2003. Pan-tropical spotted dolphins (Stenella attenuata) were the most numerous species recorded, followed by bottlenose dolphins (Tursiops truncatus) and rough-toothed dolphins (Steno bredanensis), a species not previously reported from St Helena. This last species was only recorded occurring in mixed groups with bottlenose dolphins. Pan-tropical spotted and bottlenose dolphins differed in their spatial distribution around St Helena. While pan-tropical spotted dolphins were primarily recorded resting in large groups in the lee of the island during daylight hours, bottlenose dolphins and rough-toothed dolphins were recorded closer to shore and on both the windward and lee sides. Humpback whales (Megaptera novaeangliae) were also recorded once during the survey, but interviews with local fishermen suggest that this species regularly occurs in the waters around St Helena in small numbers during the austral winter. The results of this preliminary survey suggest that the cetacean community around St Helena during this survey was relatively simple, consisting of up to three species that are present year-round and one seasonally occurring species in the nearshore waters, with a small number of additional species occurring occasionally in deeper offshore areas.

This study provides the first compilation on age and growth of some delphinids in south-eastern Brazil (18°25′S–25°45′S). A total of 154 delphinids were reported: 44 Atlantic spotted dolphin Stenella frontalis; 36 bottlenose dolphin Tursiops truncatus; 26 ‘Brazilian’ common dolphin Delphinus sp.; 20 rough-toothed dolphin Steno bredanensis; 16 Fraser's dolphin Lagenodelphis hosei; 3 false killer whale Pseudorca crassidens; 3 unidentified Stenella sp.; 2 pantropical spotted dolphin Stenella attenuata; 2 short-finned pilot whale Globicephala macrorhynchus; 1 spinner dolphin Stenella longirostris; and 1 striped dolphin Stenella coeruleoalba. Age was estimated by counting the number of growth layer groups present in the dentine in 74.5% of the sample. The growth of 92 individuals of the first five species was determined by the Gompertz model to length-at-age data. Stenella frontalis—the oldest specimen was 23 y and the asymptotic length of 224.4 cm predicted by growth curve occurred at about 20 y; T. truncatus—the oldest specimen was 26 y and the asymptotic length of 301.3 cm predicted by growth curve occurred at about 20 y; Delphinus sp.—the oldest dolphin was 18 y and the asymptotic length of 215.9 cm predicted by growth curve occurred at about 5–6 y; S. bredanensis—the oldest specimen was 24 y and the asymptotic length of 258.1 cm predicted by growth curve occurred at about 10 y; L. hosei—the oldest specimen was 19 y and the asymptotic length of 231.2 cm predicted by growth curve occurred at about 7–8 y. Only age was estimated for the other species. The age-at-length data for S. frontalis, Delphinus sp., S. bredanensis and L. hosei were consistent, suggesting a good agreement with previous work on these species. For T. truncatus, the age at asymptotic length obtained in this study might be confirmed by increasing the sample size. The information currently presented will contribute to further life history research of delphinids on the western south Atlantic coast.

Tuna purse-seiners in the eastern tropical Pacific (ETP) capture yellowfin tuna by chasing and encircling herds of associated dolphins. This fishery has caused mortality in 14 dolphin species (20 stocks) and has led to significant depletions of at least three stocks. Although observed dolphin mortality is currently low, set frequency remains high and dolphin stocks are not recovering at expected rates. Mortality of nursing calves permanently separated from their mothers during fishery operations may be an important factor in the lack of population recovery, based on the recent discovery that calves do not accompany 75%‐95% of lactating females killed in the purse-seine nets. We assessed age-specific potential for mother‐calf separations and subsequent mortality of calves by reviewing and synthesizing published data on physiological and behavioral development in delphinids from birth through 3 yr postpartum. Results indicate that evasive behavior of mothers, coupled with the developmental state of calves, provides a plausible mechanism for set-related mother‐calf separations and subsequent mortality of calves. Potential for set-related separation and subsequent mortality is highest for 0‐12-mo-old dolphins and becomes progressively lower with age as immature dolphins approach adult stamina and attain independence.

Mitochondrial DNA (mtDNA) control region sequences and microsatellite loci length polymorphisms were used to investigate genetic differentiation in spotted dolphins (Stenella attenuata) in the Eastern Tropical Pacific and to examine the intraspecific structure of the coastal subspecies (Stenella attenuata graffmani). One-hundred and thirty-five animals from several coastal areas and 90 offshore animals were sequenced for 455 bp of the mitochondrial control region, resulting in 112 mtDNA haplotypes. Phylogenetic analyses and the existence of shared haplotypes between the two subspecies suggest recent and/or current gene flow. Analyses using χ2, F ST (based on haplotype frequencies) and ΦST values (based on frequencies and genetic distances between haplotypes) yielded statistically significant separation (randomized permutation values P

Populations of northeastern offshore spotted dolphins Stenella attenuata attenuata and eastern spinner dolphins S. longirostris orientalis have been reduced because the dolphins are bycatch in the purse-seine fishery for yellowfin tuna in the eastern tropical Pacific Ocean (the 'tuna-dolphin issue'). Abundance and trends of these dolphin stocks were assessed from 12 large-scale pelagic surveys carried out between 1979 and 2000. Estimates of abundance were based on a multivariate line-transect analysis, using covariates to model the detection process and group size. Current estimates of abundance are about 640 000 northeastern offshore spotted dolphins (CV = 0.17) and 450 000 eastern spinner dolphins (CV = 0.23). For the whole period from 1979 to 2000, annual estimates of abundance ranged from 494 000 to 954 000 for northeastern offshore spotted dolphins and from 271000 to 734 000 for eastern spinner dolphins. Management actions by USA and international fishing agencies over 3 decades have successfully reduced dolphin bycatch by 2 orders of magnitude, yet neither stock is showing clear signs of recovery. Possible reasons include underreporting of dolphin bycatch, effects of chase and encirclement on dolphin survival and reproduction, long-term changes in the ecosystem, and effects of other species on spotted and spinner dolphin population dynamics.

Spotted dolphins in the eastern Pacific Ocean associate with yellowfin tuna. During the chase and encirclement phases of purse-seining for tunas, dolphin attempt to evade encirclement with the purse-seine net. We used data on evasive behavior (1982-2001) and numbers of purse-seine sets (1959-2001) to study the relationship between evasion and fishing effort. Results show that in nearshore areas first exploited by the fishery in the early 1960s, dolphins exhibited high evasion, but with a limited correlation between evasion and cumulative effort. In areas farther offshore next exploited in the mid- to late-1960s, dolphins showed high evasion and a significant correlation between evasion and cumulative effort. Dolphins in far-western and southern areas, first exploited in the late 1960s to early 1970s, exhibited low evasion, with little relationship to cumulative effort. We hypothesize that this spatial pattern is the result of two types of pressure from fishing: early effort in nearshore areas with a high risk of mortality that generated a lasting evasive response, followed by a longer period of even greater effort but with lower risk of mortality that generated evasion by longer-term learning.

Paralelo a un estudio de zooplancton (1999-2000), se hicieron observaciones a bordo de un bote inflable, sobre la presencia o ausencia de delfines a lo largo de un transecto (~8 km long) en la parte central de Bahía Culebra (24 km² ), Golfo de Papagayo. Se realizaron 34 muestreos en total y hubo avistamientos de delfines en 20 de ellos. La única especie de cetáceo observado en la Bahía fue el delfín manchado (Stenella attenuata). Estos avistamientos fueron más frecuentes durante la época lluviosa, en particular durante el mes de mayo de ambos años. La presencia de S. attenuata en Bahía Culebra podría estar asociada a la abundancia de presas potenciales como peces y moluscos (calamares), como se evidencia por las estadísticas pesqueras disponibles para la zona Pacífica de Costa RicaParallel to a zooplankton study (1999-2000) observations were made (from an inflatable boat), on the presence of dolphins along a transect (~8 km long) on the axis of Culebra Bay (24 km² ), Gulf of Papagayo, Pacific coast of Costa Rica. Dolphins were found during 20 of the 31 boat surveys conducted. The only species of cetacean found in the bay was Stenella attenuata, the spotted dolphin. These sightings were more frequent during the rainy season, particularly during the month of May of both years. The presence of S. attenuata in Culebra Bay might be associated to the abundances of fish and mollusks (their presumed prey: for example, squids), as evidenced by fishery statistics available for this zone of the Pacific coast of Costa Rica

Because many cetacean species produce characteristic calls that propagate well under water, acoustic techniques can be used to detect and identify them. The ability to identify cetaceans to species using acoustic methods varies and may be affected by recording and analysis bandwidth. To examine the effect of bandwidth on species identification, whistles were recorded from four delphinid species (Delphinus delphis, Stenella attenuata, S. coeruleoalba, and S. longirostris) in the eastern tropical Pacific ocean. Four spectrograms, each with a different upper frequency limit (20, 24, 30, and 40 kHz), were created for each whistle (n = 484). Eight variables (beginning, ending, minimum, and maximum frequency; duration; number of inflection points; number of steps; and presence/absence of harmonics) were measured from the fundamental frequency of each whistle. The whistle repertoires of all four species contained fundamental frequencies extending above 20 kHz. Overall correct classification using discriminant function analysis ranged from 30% for the 20-kHz upper frequency limit data to 37% for the 40-kHz upper frequency limit data. For the four species included in this study, an upper bandwidth limit of at least 24 kHz is required for an accurate representation of fundamental whistle contours.

The Gulf of Mexico is a subtropical marginal sea of the western North Atlantic Ocean with a diverse cetacean community. Ship-based, line-transect abundance surveys were conducted in oceanic waters (>200 m deep) of the northern Gulf within U.S. waters (380,432 km 2 ) during spring from 1996 to 1997 and from 1999 to 2001. Data from these five surveys were pooled and minimum abundance estimates were based on 12,162 km of effort and 512 sightings of at least 19 species. The most commonly sighted species (number of groups) were pantropical spotted dolphin, Stenella attenuata (164); sperm whale, Physeter macncephalus (67); dwarf/pygmy sperm whale, Kogia sitna/breviceps (58); Risso's dolphin, Grampus griseus (38); and bottlenose dolphin, Tursiops truncatus (24). The most abundant species (number of individuals; coefficient of variation) were S. attenuata (91,321; 0.16); Clymene dolphin, S. clymene (17,355; 0.65); spinner dolphin, S. longirostris (11,971; 0.71); and striped dolphin, S. coeruleoatha (6,505; 0.43). The only large whales sighted were P. macracephalus (1,349; 0.23) and Bryde's whale, Balaenoptera edeni (40; 0.61). Abundances for other species or genera ranged from 95 to 2,388 animals. Cetaceans were sighted throughout the oceanic northern Gulf and, whereas many species were widely distributed, some had more regional distributions.

A total of 447 base pairs of the mitochondrial DNA control region from 34 pantropical spotted dolphins, Stenella attenuata, in the waters of Taiwan and South China Sea were sequenced and analyzed. In this study, we tested the null hypothesis of non-differentiation genetic structure of the spotted dolphin of Taiwanese and adjacent waters. There were three putative populations in this study －Taiwan Strait, eastern Taiwan and South China Sea. The genetic structure and population differentiation of the putative populations were estimated to clarify the population status. There were 14 variable sites within the sequences and 13 haplotypes defined. Among the haplotypes, nine were unique and four were shared. The South China Sea population had three haplotypes, all of these were unique. The haplotype diversity estimates of the three populations range from 0.8883 in South China Sea, followed by 0.8182 in Taiwan Strait and 0.7778 in eastern Taiwan. Nucleotide diversity estimates range from 0.0096 in eastern Taiwan, 0.0078 in South China Sea and 0.0049 in Taiwan Strait. The Minimum-spanning network does not describe a clear pattern of haplotype and geographical locale relationship. Neighbor-joining and Maximum Likelihood phylogenetic analyses with Stenella longiroatris as outgroup also could not divide the haplotypes into clades representing the three putative populations. The Analysis of Molecular Variance (AMOVA) results show two patterns of population differentiation. The analysis using haplotype frequency, Fst, indicates significant population subdivision between South China Sea and Taiwan Strait (Fst = 0.1761, p = 0.0156), and between South China Sea and eastern Taiwan populations (Fst = 0.2029, p = 0.0059). However, the analysis using genetic distance and frequency information, Φst, does not reveal significant population differentiation between any pair of comparisons. Additionally, the relatively lower genetic diversity estimates of pantropical spotted dolphins in Taiwanese waters suggest that future monitoring is needed. A more systematic collecting method and expanding sampling area should be carried out for future investigations.

In three delphinid species (Pacific spotted dolphin, Stenella attenuata; common dolphin, Delphinus delphis; harbor porpoise, Phocoena phocoena) the enzyme lysozyme and the peptide group β-defensins are demonstrated for the first time in cetaceans as products of the thick integument. Lysozyme was found between the lamellae of the stratum corneum, in the cells of the stratum spinosum, free cells of the dermis, and in endothelial cells of dermal blood vessels. β-defensins (especially type 3) were clearly located in cells of the upper stratum spinosum, and concentrated between the upper five or six layers of the stratum corneum. The occurrence and localization of such substances that may serve as a non-specific defense against bacteria, fungi, algae, and ectoparasites, was known until now only for haired marine mammals with typical skin glands, like in pinnipeds.

Using stomach contents from 203 spotted dolphins (Stenella attenuata) killed in the yellowfin tuna fishery, we modeled the weaning process of calves. Spotted dolphins began to take solid food at approximately 6 mo of age, or 115 cm, but continued to suckle until they were nearly 2 yr old. Calves tended to feed more frequently on squid as they got older, which suggested there was a shift in diet during weaning. The average age and total body length at weaning was estimated to be 0.8 yr (approximately 9 mo) and 122 cm. The oldest suckling calf was almost 2 yr old, which suggests that some calves continued to suckle for more than a year after they could have been weaned. A better understanding of the weaning process, especially quantifying the period of time when calves are nutritionally dependent on their mothers may lead to a better evaluation of their potential vulnerability to the disturbance caused by the yellowfin tuna purse-seine fishery.

Mixed-species interactions were observed between Pantropical spotted dolphins, Stenella attenuata, and spinner dolphins, Stenella longirostris ,i n Hawaiian waters between 1996 and 1998. Yearround observations were made of spinner dolphins entering a shallow bay off the Waianae (western) coast of Oahu. Mixed-species observations occurred on 19 days between 1996–1998. Spinner dolphins were typically present in greater numbers than spotted dolphins with ratios as high as 75:1. Interspecific behaviours observed include aggression, copulation, and travelling. Five aggressive interactions are described in detail. These behavioural observations are similar to those observed between other delphinid species around the world and suggest that sympatric delphinid species may be more common than previously reported and may have common communication and social signals.

carcasses beached or floating at sea, which often bear signs of shark predation. Still, in some cases, these animals could have died of other causes and may have been scavenged after death (Carey et al., 1982; Long & Jones, 1996; Heithaus, 2001b). Witness accounts of shark predation on cetaceans are rare. On this occasion, a 3.5 -4.0 m tiger shark (Galeocerdo cuvier) successfully attacked a juvenile spotted dolphin (Stenella attenuata) near Penguin Bank, O′ahu, Hawaii on 11 March 2000. The event was witnessed by the author from a Partenavia P-68 Observer aircraft during an aerial survey assessing abundance and distribution of odontocetes. The dolphin was swimming in a school of 30-50 individuals heading in a south-easterly direction. There are few published observations of direct attacks by sharks on live cetaceans (Leatherwood et al., 1973; Mann & Barnett, 1999). The following report documents an attack by a tiger shark on a juvenile spotted dolphin in Hawaiian waters. Materials and Methods

The possible behavioral and physical problems involving cetaceans and marine seismic surveys have attracted the interest and concern of several authors. However, studies on cetaceans frequenting Nigerian waters have not been detailed in literature. This research work is appropriately driven by these requirements. Opportunistic data was collected on board six different marine vessels belonging to ExxonMobil. Data collected were analyzed using descriptive statistics, t-test and ANOVA at p=0.05. A total of 8,327 hours 36 minutes observation effort was accomplished during twenty-six months, representing almost 800 km 2 of coverage. Two hundred and eighty-three (283) sightings were recorded comprising of 189 (66.78%) sightings of whales and 94 (33.22%) sightings of dolphins. Four species of cetaceans were identified, bottlenose dolphins ( Tursiops truncatus ) were the most abundant followed by pantropical spotted dolphins ( Stenella attenuata ). These two species occurred throughout the sampling months, while the predominant whales specie were the humpback whale (Megaptera novaeangliae) and killer whales ( Orcinus orca ) which seem to be present in just a part of the year. Whales were sighted more when the guns were active. Conversely, less of the dolphins were sighted while the guns were active. There were significant differences (P=0.05) regarding the air-gun operational state between the number of whales and dolphins sightings. The result suggests that swimming behavior was dependent of air-gun operational state. Keywords : Cetaceans, seismic survey, Sightings, Akwa Ibom state, south-south Nigeria.

The lateral enamel lamina (LEL) is a part of the enamel organ, which is probably not involved in tooth formation. It represents, besides the "stalk" of the tooth primordium, a second interconnection between enamel organ and oral epithelium or vestibular lamina. We detected the LEL in the sheep (Ovis aries), the dolphin (Stenella attenuata), and the vole (Microtus agrestis) by light microscopy and computer-aided three-dimensional reconstruction. The LEL could be found in cap to bell stage tooth primordia, most clearly in slowly developing tooth germs. LEL-like structures have been furthermore described or depicted in tooth germs of the mouse, the elk (Alces alces), the dugong (Dugong dugong), the elephant (Loxodonta africana), and the human. Probably it is a part of all mammalian tooth primordia that undergoes regression during morphogenesis of the enamel organ. As a reducing structure, it should be considered in studies of tooth development.

17. Pantropical Spotted Dolphin Stenella attenuata French: Dauphin bridé / German: Schlankdelfin / Spanish: Delfin manchado tropical Other common names: Bridled Dolphin, Narrow-snouted Dolphin, Slenderbeaked Dolphin, Spotted Porpoise, Whitespotted Dolphin; Offshore Pantropical Spotted Dolphin (attenuata); Coastal Pantropical Spotted Dolphin, Graffman’s Dolphin (graffmani) Taxonomy. Steno attenuatus Gray, 1846, type locality unknown. Later designated by J. E. Gray in 1850 as “Inhab. Cape Horn.” The genus Stenella is likely polyphyletic, and taxonomy of its member species probably will be revised in the near future. According to molecular studies, S. frontalis 1s most closely related to S. coeruleoalba and S. clymene, followed by Delphinus and Tursiops aduncus. These species appear to be more closely related to each other than any of them are to 1. truncatus, S. attenuata, or S. longirostris. Similarities in appearance between S. attenuata and S. frontalis are thus likely due to homoplasy or pleisiomorphy. Two subspecies recognized. Subspecies and Distribution. S.a.attenuataGray,1846—Pantropicalinalloceansbetweenc.40°Nand¢.40°S,includingRedSea,ArabianSea,PersianGulf,andBayofBengal,butexcludingtheMediterraneanSea. S. a. graffmani L.onnberg, 1934 — near-shore coastal waters of the Pacific coast of Mexico, Central America, and South America to Peru. Descriptive notes. Total length 160-260 cm (males) and 160-240 cm (females); weight up to 119 kg. Neonates are 80-85 cm long and weigh c.10-15 kg. The “Coastal Pantropical Spotted Dolphin” (S. a. graffmani) tends to be slightly larger in size than the “Offshore Pantropical Spotted Dolphin” (S. a. attenuata). Overall, the Pantropical Spotted Dolphin has slender body shape, but the Coastal Pantropical Spotted Dolphin tends to be more robust. Beak is long and skinny, but it is slightly thicker in the Coastal Pantropical Spotted Dolphin. Dorsal fin is moderately sized, narrow, and falcate with pointed tip. Flippers are slender and curved, also with pointed tips. Adult males may have slight anal protuberance. The Pantropical Spotted Dolphin has countershaded color pattern underlying numerous white spots. Skin is pale gray except for a dark-gray dorsal cape that sweeps low over flanks. Offshore Pantropical Spotted Dolphins have varying degrees of spotting, and some adults may have very little to none at all. Spotting is generally heaviest in Coastal Pantropical Spotted Dolphin, sometimes obscuring cape entirely. Lips and beak tip are usually white. There are a few dark gray stripes on face and head: “mask” stripe across front of melon above beak between two dark rings around eyes, and stripe extending from anterior base of flipper to corner of mouth and onto lower jaw. Youngest individuals do not have spots, and areas that are pale gray on adults are white on young. As they grow, white areas darken to pale gray, and dark spots develop first on ventral body, followed by white spots on flanks and back. As individuals age, dark ventral spots may fuse and fade, leaving only white flank and dorsal spots. There are 34-48 pairs of slender, conical teeth in each jaw. Habitat. Offshore and around oceanic islands. The Pantropical Spotted Dolphin is the most abundant delphinid species in the eastern tropical Pacific Ocean. The Offshore Pantropical Spotted Dolphin tends to be more abundant around the Hawaiian Islands, some Caribbean islands, Philippines, and Taiwan. In these regions, they may be observed in shallower waters. Overall, the Pantropical Spotted Dolphin is more abundant in lower latitudes of its distribution. Offshore populations prefer tropical surface water characterized by a shallow thermocline (less than 50 m deep), sea-surface temperatures more than 25°C, and salinity less than 34 ppt. In the south-western Atlantic Ocean, the Offshore Pantropical Spotted Dolphin is found beyond the continental shelf in waters more than 850 m deep, and in the Gulf of Mexico, they are found in continental slope waters more than 1000 m deep. Food and Feeding. The Pantropical Spotted Dolphin is known to feed on small epipelagic fish, cephalopods, and crustaceans. It is an opportunistic feeder whose diet varies by season and geographical region. The Offshore Pantropical Spotted Dolphin seems to prefer lanternfish (Myctophidae), flying squid (Ommastrephidae), and flying fish (Exocoetidae). They forage nocturnally and exploit the rising deep scattering layer. Around the Hawaiian Islands, nocturnal foraging activity is characterized by deeper dives than those observed during the day. At night, average dive is 57 m, but it is only 12:8 m during the day. Off Taiwan, diet of the Pantropical Spotted Dolphin is known to include some mesopelagic species. The Coastal Pantropical Spotted Dolphin seems to specialize more on larger benthic species. Natural predators may include the Killer Whale (Orcinus orca), the False Killer Whale (Pseudorca crassidens), the Pygmy Killer Whale (Melon-headed Whale), and the Short-finned Pilot Whale (Globicephala macrorhynchus). The Pantropical Spotted Dolphin associates with yellowfin tuna (Thunnus albacares) in the north-eastern tropical Pacific Ocean, which may be related to foraging efficiency. Breeding. The Pantropical Spotted Dolphin may breed throughout the year, but breeding peaks in spring and autumn. Gestation lasts c¢.11-5 months, and young are weaned at 1-2 years of age. Breeding females will typically give birth once every 2-3 years. Females reach sexual maturity at 9-11 years of age, and males at 12-15 years. Activity patterns. The Pantropical Spotted Dolphin is a fast swimmer (sprint swims may exceed 22 km/h), and itis known to be aerially active. Breaching and side slapping are common, particularly among juveniles. Pantropical Spotted Dolphins will also readily approach boats and bow-ride, but they have learned to avoid boats in regions frequented by tuna fisheries. Dives can last up to 3-4 minutes. Movements, Home range and Social organization. The Pantropical Spotted Dolphin is gregarious, and group sizes range from a few to several thousand individuals. Group sizes of the Coastal Pantropical Spotted Dolphin tend to be smaller (less than 100) than those of the Offshore Pantropical Spotted Dolphin. Average group sizes from different regions range from 90 individuals to 170 individuals. Sex and age classes may segregate into smaller subgroups within a large group. Mother—offspring pairs, adult males, and juveniles tend to remain within their own subgroups. In the eastern tropical Pacific Ocean, the Pantropical Spotted Dolphin may associate with yellowfin tuna, the Spinner Dolphin (S. longirostris), and skipjack tuna (Katsuwonus pelamas). Tuna fishermen sometimes take advantage of these tuna—dolphin associations. Immature Pantropical Spotted Dolphins and younger adults tend not to associate with tuna as often as full adults do. Tuna association also occurs in the western Indian Ocean. Off Hawaii, interactions between Pantropical Spotted Dolphins and Spinner Dolphins include traveling, aggression, and sexual activity. Little is known about migration and movement patterns of either species. Off coastal Japan, Pantropical Spotted Dolphins are known to migrate seasonally between the northern boundary of the Kuroshiro Current in summer and southern Japan in October-November. Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. The Coastal Pantropical Spotted Dolphin has not yet been assessed independently. Abundance estimates for the Pantropical Spotted Dolphin total more than 2-5 million, and there are still populations that have not yet been assessed. The Offshore Pantropical Spotted Dolphin in the north-eastern tropical Pacific Oceanhas declined 76% overthe last three generations (c.70 years), but this decline has since stopped and did not contribute to significant overall global decline. Nevertheless, this population does not appear to be recovering. The most recent estimate for this population was 737,000 individuals. Lack of recovery could be due to fishery-related stress and an underreporting of current catch rates, offspring separation or orphaning, or ecosystem change. Abundance of Coastal Pantropical Spotted Dolphins is estimated at 228,038 individuals. The population of Pantropical Spotted Dolphins in the south-western Pacific Ocean consists of 876,075 individuals. There are 8978 individuals off Hawaii, 34,067 individuals in the Gulf of Mexico, and ¢.15,000 individuals off the Philippines. Separate assessments of populations and subspecies have been recommended, given that some, such as the population in the north-eastern tropical Pacific Ocean, will likely have a threatened status at this scale. Japan has taken large numbers of small cetaceans in drive fisheries, including the Pantropical Spotted Dolphin, for human consumption since at least 1959. In 1995-2004, annual catch rate was c.129 individuals, and this is thought to have influenced a decrease in the age of female maturity in the local population of the Pantropical Spotted Dolphin. The Pantropical Spotted Dolphin is also taken by harpoon and gillnets in the Philippines, Laccadive Islands, Indonesia, India, and Sri Lanka. Taiwanese pelagic driftnet fisheries also likely have high incidental catch rates, but these fisheries are not currently monitored. A drive fishery in the Solomon Islands has taken several hundred to several thousand Pantropical Spotted Dolphins yearly since the 1960s and continues today. The now depleted population of Pantropical Spotted Dolphin in the north-eastern tropical Pacific Ocean was once heavily caught in tuna purse-seine fisheries due to tuna—dolphin associations. About 4-9 million Pantropical Spotted Dolphins were estimated killed in this fishery in 1959-1972. This kill was reduced to ¢.15,000 ind/year during the 1990s due to improved dolphin rescue procedures. Implementation of mortality limits by the Inter-American Tropical Tuna Commission also greatly reduced incidental catch rates. In 2005, only 373 Pantropical Spotted Dolphins were incidentally caught in these fisheries. Off Iki Island, Japan, fishermen are given bounties for killing dolphins to keep them from interfering with long-line fisheries. In 1976-1982, 538 Pantropical Spotted Dolphins were killed in these culls. Incidental catch does not appear to be a major threat in other areas. Tourism may be a growing problem in some regions, such as Costa Rica, where presence of dolphin-watching vessels is known to reduce time Pantropical Spotted Dolphins spend feeding and resting. Bibliography. Archer & Robertson (2004), Archer et al. (2004), Baird et al. (2001), Cramer et al. (2008), Escorza-Trevino et al. (2005), Gerrodette & Forcada (2005), Gray (1850), Hammond et al. (2008;j), LeDuc et al. (1999), Montero-Cordero & Lobo (2010), Noren & Edwards (2007), Perrin (2009a), Perrin & Hohn (1994), Psarakos et al. (2003), Wade et al. (2007), Wang & Yang Shihchu (2007)., Published as part of Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, pp. 410-526 in Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona :Lynx Edicions on pages 410-526, DOI: 10.5281/zenodo.6610922

Cetacean middle ears are unique among mammals in that they have an elongated tympanic membrane, a greatly reduced manubrium mallei, and an incudal crus longum that is shorter than the crus breve. Elongation of the tympanic membrane and reduction of the manubrium is thought to be related to an evolutionary rotation of the incus and malleus out of the plane of the tympanic membrane. We examined if rotation also occurs during ontogeny by comparing the middle ears of two species of dolphins (Delphinus delphis, Stenella attenuata) at different stages of development. We observed that: the incus has the body and crural proportions as in terrestrial mammals early in development; the incudomallear complex rotates approximately 90 degrees following ossification; the tympanic membrane is not elongated until relatively late in development. Therefore, some of the unique characteristics of the cetacean middle ear develop as modifications of an initially terrestrial-like morphology.

The kill of dolphins (Stenella attenuata and S. longirostris) in the eastern tropical Pacific tuna purse-seine fishery has been underestimated because of unobserved deaths of nursing calves due to separation from their mothers during fishing. Based on an analysis of dolphins killed from 1973 to 1990, and depending on the length at which calves are assumed to become independent, there was a deficit of calves relative to the number of lactating females killed in 24%-32% of 1,847 spotted-dolphin sets and in 13%-19% of 563 spinner-dolphin sets. We found a deficit of 0.31-0.45 spotted dolphin and 0.15-0.26 spinner dolphin calves per set. If these missing calves were added to the observed kill, it would represent an increase in the kill of 10%-15% for spotted dolphins and 6%-10% for spinner dolphins in the sets we examined. We did not attempt to estimate the actual number of unobserved calf deaths due to purse-seine fishing on dolphins, either in the sets we examined or in all dolphin sets. The actual number of unobserved calf deaths is likely to be higher than the calf deficit we found. Separation of dolphin mothers from calves could occur at any of several points in the fishing process, but most of these would be invisible to us and not produce a calf deficit. Estimation of the actual number of unobserved calf deaths would require further information on how frequently permanent mother-calf separations occur, the fraction of calves that survive after separation, the fraction of lactating females set upon that are carrying calves, and the fraction of calves killed that are actually related to lactating females killed in the same set. In any case, the observation of a calf deficit indicates that the reported dolphin kill fails to measure the full impact of purse-seine fishing on spotted and spinner dolphin populations.

A complex lymphoepithelial gland is a constant feature in the larynx of Atlantic bottlenose dolphins, Tursiops truncatus, based on study of 56 animals. Larynges were removed from fresh, non-decomposed beach-stranded animals for gross examination and histological sampling. A large lymphoepithelial gland occurs in the rostro-ventral mucosa of the larynx, overlying the cricoid cartilage. It presents as a well-defined, elevated, and heavily trabeculated area. Histological examination reveals a pseudostratified columnar epithelium which branches into the underlying submucosa. The epithelial-lined folds and crypts thus formed are surrounded by aggregations of lymphocytes, which infiltrate this epithelium. Mucous glands are often associated with these lymphoid aggregations. The histological appearance of the laryngeal gland is remarkably similar to the palatine, or dorsal oropharyngeal tonsils, of T. truncatus. It may be analogous to the nasopharyngeal adenoid of terrestrial animals. Age-related involution of the laryngeal gland is not as obvious with increasing animal age (or length) as it is in other mucosa-associated lymphoid tissue. The distribution of this gland among cetaceans is not yet known. We have observed it in individuals of every species we have studied, including Lagenodelphis hosei, Stenella coeruleoalba, Stenella attenuata, Globicephala macrorhynchus, Steno bredanensis, Physeter catodon, Pseudorca crassidens, Mesoplodon europaeus, and Kogia breviceps.

We conducted a cetacean survey in the pelagic western tropical Indian Ocean (WTIO) aboard an 85-m research vessel from March to July 1995, covering 9,784 linear km. Using 25 × binoculars and line-transect methods, we recorded 589 sightings of 21 species. Stenella longirostris was the most abundant cetacean, in terms of number of individuals sighted, by an order of magnitude above any other species, while Physeter macrocephalus was the most frequently sighted, in terms of number of schools. Twelve species were widespread, seven were rare, and two were localized; our sightings include new distributional records for 12 species. Significant observations included the following: (1) Delphinus cf. tropicalis was abundant off the coast of Oman (16 sightings) and readily distinguishable in the field from D. delphis and D. capensis, (2) Balaenoptera musculus was fairly common and localized in the area of the Maldives (17 sightings), and (3) three sightings were made of an unidentified bottlenose whale tentatively referred to as Indopacetus (i. e., Mesoplodon) pacificus. We recorded 26 mixed-species cetacean schools, 43 schools with which seabirds associated, and 17 schools associated with tuna. Notable among these were mixed aggregations of Stenella attenuata, S. longirostris, yellowfin tuna, and seabirds. The cetacean community of the WTIO was similar to that of the eastern tropical Pacific (ETP) and the Gulf of Mexico (GM) in several respects. First, differences in abundance rank of individual species were small, with the result that common species were common and rare species were rare, regardless of ocean. Second, these differences in abundance were due primarily to differences in encounter rate, which varied with ocean by as much as 3,000%, and less so to school size, which generally varied less than 100%. Third, regardless of ocean, three species comprised the majority of cetaceans in the community, Stenella attenuata, S. longirostris, and S. coeruleoalba, representing 62%-82% of all individuals for all species. However, the rank order of abundance for these three species differed with ocean. Most notably, S. attenuata was abundant in the ETP and GM (abundance rank = 2 and 1, respectively) but much less common in the WTIO (abundance rank = 6). Although habitat preferences for S. attenuata appear to overlap considerably with those of S. longirostris in the ETP, our results suggest there may actually be significant differences between these two species. Detailed analysis of oceanographic correlates of distribution will be necessary in order to understand fully the habitat requirements of these pelagic dolphins, often the most conspicuous elements of tropical cetacean communities around the world.

The physical habitat of cetaceans found along the continental slope in the north-central and western Gulf of Mexico was characterized from shipboard sighting data, simultaneous hydrographic measurements, and satellite remote sensing. The study area was encompassed by the longitude of the Florida-Alabama border (87.5°W), the southernmost latitude of the Texas-Mexico border (26.0°N), and the 100-m and 2,000-m isobaths. Shipboard surveys were conducted seasonally for two years from April 1992 to May 1994. A total of 21,350 km of transect was visually sampled in an area of 154,621 km2. Sighting localities of species in the study area were differentiated most clearly with bottom depth. Atlantic spotted dolphins (Stenella frontalis) were consistently found in the shallowest water on the continental shelf and along the shelf break. In addition, the bottom depth gradient (sea floor slope) was less for Atlantic spotted dolphins than for any other species. Bottlenose dolphins (Tursiops truncatus) were found most commonly along the upper slope in water significantly deeper than that for Atlantic spotted dolphins. All the other species and species categories were found over deeper bottom depths; these were Risso's dolphins (Grampus griseus), short-finned pilot whales (Glob-icephala macrorhynchus), pygmy/dwarf sperm whales (Kogia spp.), roughtoothed dolphins (Steno bredanensis), spinner dolphins (Stenella longirostris), sperm whales (Physeter macrocephalus), striped dolphins (Stenella coeruleoalba), Mesoplodon spp., pantropical spotted dolphins (Stenella attenuata), Clymene dolphins (Stenella clymene) and unidentified beaked whales (Ziphiidae). Risso's dolphins and short-finned pilot whales occurred along the upper slope and, as a subgroup, were significantly different from striped dolphins, Mesoplodon spp., pantropical spotted dolphins, Clymene dolphins, and unidentified beaked whales, which occurred in the deepest water. Pygmy/dwarf sperm whales, rough-toothed dolphins, spinner dolphins, and sperm whales occurred at intermediate depths between these two subgroups and overlapped them.

Evaluating the effect of parasites on population size is essential for designing management and conservation plans of wild animal populations. Although knowledge in this area is scarce in cetaceans, current evidence suggests that species of the nematode genus Crassicauda may play an important regulatory role in some populations. In the present study, a semiparametric regression technique is applied to a previously published dataset to re-examine the role of Crassicauda sp. in natural mortality of pantropical spotted dolphins Stenella attenuata. The resulting model indicated parasite-induced mortality at ages between 6.5 and 9 years and at roughly 12 years. The maximum mortality estimates obtained could represent 2-4% of natural mortality in dolphins 6-8-year old. This estimate is substantially smaller than previously published values, but in contrast with previous research, the present model provides clear statistical evidence for parasite-induced mortality because the bootstrapped 95% confidence intervals of the estimated mortality rates excluded the zero value. The present study also evaluates, through simulations, how potential sampling biases of infected dolphins could overestimate parasite-induced mortality. Small differences in sampling selectivity between infected and uninfected animals could substantially reduce the mortality estimates. However, the simulated models also supported the notion of statistically significant mortality in juvenile dolphins. Given that dolphins older than 16 years were poorly represented in the dataset, further research is needed to establish whether Crassicauda sp. causes meaningful mortality for population dynamics among adult individuals.

Externally, the flippers of Cetacea resemble fish fins, but their internal structure is entirely mammalian. They show, however, some adaptative deviations from the typical pattern of the mammalian extremities, the most striking of which is an increased number of phalanges. The aim of this study is to describe the course of the development of flippers in the spotted dolphin (Stenella attenuata) and compare its features with other similar species from an evolutionary perspective. Early stages of flipper development were studied histologically. Differentiation of cartilaginous anlagens of the skeleton progresses proximodistally, condensation in digital rays being evident sooner than chondrogenesis in the carpal region. In one specimen, the temporary presence of cartilaginous rudiments of two carpal elements, which are not found in adults, was observed. At all examined stages, phalangeal number progressively increases up to (radial to ulnar) 3, 7, 7, 5, 3 in the most advanced stage. The reason for this condition is the specialised function of these limb-like structures. It is a classical example of convergence, in which mammalian extremities change their form to emulate the fin function. A similar condition is found in another group of originally terrestrial animals secondarily fully adapted to the aquatic mode of life-Ichyosauria (Reptilia).

In order to comprehend better the distribution of Gulf of Mexico cetaceans, all available records of whales and dolphins in the offshore Gulf were assembled and analysed. This included sightings, strandings and captures of all species, except the Bottlenose Dolphin Tursiops truncatus, from all sources, except the recently completed GulfCet project. An attempt was made to confirm species identification for each of the records. A total of 1223 records was available for analysis. Twentyseven species of cetaceans have been confirmed to occur in the offshore Gulf of Mexico. All of the baleen whales, with the possible exception of the Bryde's Whale Balaenoptera edeni appear to be extralimital in the Gulf. The Sperm Whale Physeter macrocephalus is, by far, the most common great whale in this body of water. All previous records of Common Dolphins Delphinus spp. in the Gulf are rejected as either incorrect or unreliable, and there is currently no convincing evidence that dolphins of the genus Delphinus occur in the Gulf. The Atlantic Spotted Dolphin Stenella frontalis is the only species, other than the Bottlenose Dolphin, that regularly occurs over the continental shelf. The Pantropical Spotted Dolphin Stenella attenuata is the most common species of small cetacean in oceanic waters of the Gulf, but many other species also occur there in significant numbers.

The Cetacea are group of animals which have completely lost their hind limbs during the course of evolution as a result of their entirely aquatic mode of life. It is known, however, that during their embryonal period, the hind limb buds are temporarily present. The control mechanisms of this regression are not yet understood, and vestigial limbs can sometimes be found in adults. The aim of the present study is to describe the course of hind limb rudimentation during prenatal development of Stenella attenuata (Spotted dolphin) at tissue and cell levels and compare the results with other natural or experimentally induced amelias. Hind limb buds of dolphin embryos, CRL 10-30 mm, were examined histologically. Before total disappearance, they show histodifferentiation comparable with other mammals. Initially, they form the apical ectodermal ridge, which soon regresses. The mesenchyme undergoes the process of condensation to form anlagens of prospective skeletal elements. These condensations are surrounded by vascular plexuses. During the course of rudimentation, some mesenchymal cells die, while the others are incorporated into the body wall. Nerve ingrowth into rudimentary limb buds was also detected. The temporary presence of hind limb rudiments in cetacean embryos can be regarded as a good example of recapitulation of phylogenesis in ontogenesis.

Ontogeny and variation of head stripes were investigated in Stenella attenuata, S. longirostris, and Delphinus delphis. The eye stripe and the blowhole stripe together comprise the bridle. The Anlage of the bridle is a line extending across the back of the head in small fetuses. As the blowhole moves posteriorly and the rostrum lengthens, an inflection point develops in the line above the eye. This point moves forward, creating a progressively greater triangular area between the incipient eye and blowhole stripes. Well before birth, the inflection point is close to the apex of the melon, and the eye and blowhole stripes are narrow and well defined. This process proceeds to varying degrees in the other delphinoids. For example, in Peponocephala electra and in Cephalorhynchus spp., the inflection point migrates only part of the way to the apex of the melon, and the resulting “blowhole stripe” remains a broad caplike feature, resembling the state of development in small fetuses of Stenella and Delphinus. A simple eye spot without a stripe may be primitive, as it occurs in non-delphinoid cetaceans. Presence of the bridle only in the delphinids and phocoenids may unite them in a clade exclusive of the monodontids.