Stenella Longirostris Research Articles

Broadband recording of social acoustic signals of the Hawaiian spinner and spotted dolphins

The social and communication signals of several species of free-ranging delphinids have been analyzed and characterized by a number of workers over the past 3 decades. Most of the past works have used bandlimited recording equipment and have focused on the sonic components of the signals. Therefore, most discussions of delphinid whistles and nonecholocation pulsed signals have been limited almost exclusively to below approximately 20 kHz. A technique has been developed that allows one to collect high-fidelity recordings of signals up to 55 kHz in frequency. By digitizing signals directly into a laptop computer through a PCMCIA A/D converter, the sonic and ultrasonic components of the whistles and burst pulses of two populations of Hawaiian spinner and spotted dolphins (Stenella longirostris and S. attenuata) resident along the leeward coast of Oahu, Hawaii are being studied. Preliminary results show that the ultrasonic range above 20 kHz is rich with whistle harmonics and components of pulsed signals.

Comparison of the whistle structure of six species of dolphin

Spectral and statistical analyses were used to compare the whistle structure of six species of dolphin; Stenella longirostris, Stenella frontalis, Stenella attenuata, Lagenorhynchus obscurus, Tursiops truncatus, and Sotalia fluviatilis. A consistent pattern existed in the various coefficients of variation calculated for the different species. In general, the frequency variables had the lowest coefficients of variation (cv). The values of cv for maximum frequency were usually the lowest. Compared to other species Tursiops had relatively large coefficients of variation of the frequency variables indicating that the frequencies of Tursiops whistles were more diverse. The other five species had similar frequency ranges which had higher upper frequencies than Tursiops. The results of discriminate analysis indicated that here were significant differences between the whistle structures of the different species, and that these differences were related to taxonomic relations, body size, and habitat. The magnitude ...

The Hawaiian spinner dolphin

Twenty years in the making by a distinguished dolphin expert and his associates, Hawaiian Spinner Dolphin is the first comprehensive scientific natural history of a dolphin species ever written. From their research camp at Kealakeakua Bay in Hawaii, these scientists followed a population of wild spinner dolphins by radio tracking their movements and, with the use of a windowed underwater vessel, observing the details of their underwater social life. The authors begin with a description of the spinner dolphin species, its morphology and systematics, and then examines the ocean environment, the organization of dolphin populations, and the way this school-based society of mammals uses shorelines for rest and instruction of the young. The dolphins' reproductive cycle, their vision, vocalization, hearing, breathing, and feeding, and the integration of the school are carefully analyzed. The authors conclude with a comprehensive evolutionary analysis of this marine cultural system, with its behavioral flexibility and high levels of cooperation. This absorbing book is the richest source available of new scientific insights about the lives of wild dophins and how their societies evolved at sea.

Parkinson's Petrel Distribution and Foraging Ecology in the Eastern Pacific: Aspects of an Exclusive Feeding Relationship with Dolphins

During 28 research vessel cruises in the eastern tropical Pacific Ocean from 1976 through 1990, Parkinson's Petrels (Procellaria parkinsoni) were observed near shore from southern Mexico (ca. 15°N) to northern Peru (ca. 5°S), and along a broad seaward extension that continued west of the Galápagos Islands to 110°W. Parkinson's Petrels regularly associated with dolphins: of the 618 petrels observed, 469 (76%) were associated with 10 species of dolphins, on 55 occasions, with 1 to 300 petrels present. They occurred mostly with two rare dolphin species: the melon-headed whale (Peponocephala electra) and the false killer whale (Pseudorca crassidens). This appeared to be a largely obligatory foraging relationship for Parkinson's Petrels. Associations with other dolphin species occurred primarily when those species also associated with melon-headed and false killer whales. Parkinson's Petrels avoided a common and widespread, multi-species feeding assemblage which consisted of a diverse, fast-moving group of seabirds, spotted and spinner dolphins (Stenella attenuata and S. longirostris), and tuna, all of which feed on live prey forced to the surface. The lumbering Parkinson's Petrels appeared ill-equipped to take such prey. In contrast, melon-headed and false killer whales apparently fed by dismembering large prey below the surface and so, provided feeding opportunities for a scavenging bird with diving capabilities. Among eastern tropical Pacific (ETP) seabirds, Parkinson's Petrels alone are adapted for recovering food scraps well below the surface. Parkinson's Petrels appear to be more dependent on marine mammals for foraging than any other species of seabird studied and feed diurnally more than was previously thought.

Dolphin days: the life and times of the spinner dolphin

Dolphin days: the life and times of the spinner dolphin

Animal Sonar: Processes and Performance

<i>Animal Sonar: Processes and Performance</i>

Seasonal changes in distribution and habitat differences among dolphins in the eastern tropical Pacific

Large-scale patterns of dolphin distribution and oceanography were studied from research-vessel surveys conducted in the pelagic eastern tropical Pacific dunng June to November 1982, 1986 and 1987. Substantial changes were observed in relation to previously reported winter distributions for spotted and/or spinner dolphin schools (Stenella attenuata and/or S. 1ongirostris)and for striped dolphin schools (S. coeruleoalba). These dolphin species were sighted in abundance west of 120W along 10N coincident with seasonal shoaling of a thermocline ridge. No seasonal distribution changes were observed for common dolphin schools (Delphinus delphis); as in the winter, they occupied upwelling-modified waters of the region. Highest-density areas for the 3 school types were clearly separated spatially, and the thermocline depths and sigma-t's of sighting localities were statistically different between spottedlspinner dolphin schools and common dolphin schools. Striped dolphin schools could not be discriminated from the other 2 types based on these habitat variables, indicating other factors or processes contribute to the observed spatial separation of the 3 distributions.

A DWARF FORM OF THE SPINNER DOLPHIN (STENELLA LONGIROSTRIS) FROM THAILAND

AbstractA very small form of the spinner dolphin has been found to inhabit the Gulf of Thailand. Ten specimens taken incidentally in a local shrimp fishery differ from specimens of this species collected elsewhere in body size and shape, skull size and shape, number of teeth and numbers of thoracic and lumbar vertebrae. Four cranially adult males were 129–137 cm long, well below the ranges for the Indian Ocean, western Pacific, central Pacific, eastern Pacific and Atlantic. The skull is also very small. Tooth counts and vertebral counts average lower than in other series. The color pattern is not significantly different from that of spinner dolphins in the central and western Pacific, Atlantic and Indian Oceans but differs from that of the small eastern spinner of the eastern Pacific. The Gulf of Thailand specimens are morphologically separable from all other specimens, but it is to be expected that when larger samples are available there will be some overlap. The dwarf form may overlap in body and skull size with small spinner dolphins taken incidentally in a gillnet fishery for sharks off northern Australia. The geographic range of the dwarf spinner may be restricted. The size and status of the population and the impact of the shrimp fishery are unknown and should be investigated. The dwarf spinner may have an ecology different from that of other spinners, feeding mainly on reef‐associated and benthic organisms rather than mesopelagic animals.

GEOGRAPHIC VARIATION IN TOOTH MORPHOLOGY AND DENTINAL PATTERNS IN THE SPINNER DOLPHIN, STENELLA LONGIROSTRIS

AbstractSixteen tooth characters were analyzed in 277 specimens of spinner dolphins (Stenella longirostris) from the eastern tropical Pacific to determine whether the characters were associated with size of the animal, species‐stock membership or geographic location. The tooth characters included 5 continuous measurements and 11 qualitative variables. Statistical analyses of the characters included two‐way ANOVA tests which assessed continuous measurement variables for differences based on stock membership, latitude and longitude of collection or whether the animal was collected north or south of the equator. Principal component analyses combined factors of continuous variables with those of qualitative variables into components which were used as variables in further analyses. Discriminant analyses were performed using continuous variables alone and using principal components as potentially discriminating variables. Results showed that tooth differences were not associated with size but significant differences were found in some tooth variables with stock membership, incremental changes in latitude and whether the animal was collected north or south of the equator. A discriminant function, containing only tooth length, correctly classified 67% of northern and 78% of southern animals according to location of collection north or south of the equator.

RELATIVE ABUNDANCE, DISTRIBUTION AND INTER‐SPECIFIC RELATIONSHIP OF CETACEAN SCHOOLS IN THE EASTERN TROPICAL PACIFIC

AbstractThe relative abundance of the most common cetacean schools in the eastern tropical Pacific Ocean for 1977–1980 are estimated based on encounter rates with tuna purse‐seiners. No temporal trends were apparent in the relative abundance estimates. The geographic distributions for eight different school types are described. Multivariate statistical techniques are used to investigate interrelations between species and relationships to parameters of the physical environment. The results suggest three major species groupings: (1) an inshore grouping of bottlenose dolphins (Tursiops truncates), Risso's dolphin (Grampus griseus), pilot whales (Globicephala macrorhynchus) and, to a lesser extent, common dolphins (Delphinus delphis); (2) an offshore pelagic grouping of spotted and spinner dolphins (Stenella attenuate and S. longirostris); and (3) an association between pilot whales and common dolphins that overlaps the first grouping in inshore areas and also tends to be segregated from the second grouping. The results also suggest that relative densities of different school types are strongly related to physical environmental parameters, the most important being sea surface temperature, depth of the thermocline and thickness of the oxygen minimum layer.

Variation in Spinner Dolphins (Stenella longirostris) from the Eastern Tropical Pacific Ocean: Sexual Dimorphism in Cranial Morphology

Four meristic and 32 morphometric cranial characteristics were analyzed for sexual dimorphism in 200 adult spinner dolphins ( Stenella longirostris ) from the eastern tropical Pacific Ocean (ETP). Specimens were first separated into “whitebelly” and “eastern” forms based on external criteria and compared in a two-way ANOVA of color versus sex. Differences between the two color forms were minor, thus allowing the specimens to be pooled for subsequent analyses of sexual dimorphism. We assessed animals from nine 5° latitude-longitude blocks containing four or more individuals with a two-way ANOVA involving sex and geographic block. Sexual dimorphism was significant in 13 of the 36 characters and ranged from 0.04 to 11.32% difference. We could correctly identify 67% to 69% of the specimens to sex based on a discriminant function involving six characters (three rostral widths, a tooth width, the length of the temporal fossa, and one braincase measure). Classification functions are included to classify unknown specimens to sex. In addition, correction terms are included that will enable investigators to adjust measurements and factor out sexual differences in studies where it is advantageous to treat the sexes simultaneously. Trends in sexual dimorphism were very similar to those found in spotted dolphins ( S. attenuata ) from the same geographic region, although the differences were less pronounced in the spinners.

Seabird Interactions with Dolphins and Tuna in the Eastern Tropical Pacific

Bird flocks associated with dolphins in the eastern tropical Pacific are described from observations obtained during eight cruises that took place from January to March of 1976, 1977, 1979, and 1980. In the northern tropical waters between latitudes 5N and 30N, 43% to 53% of bird flocks co-occurred with dolphins. In equatorial and southern subtropical waters between latitudes SON to 12s and in the central Pacific less than 8% of the flocks were associated with dolphins. In northern tropical waters about 70% of dolphin schools associated with flocks were composed of spotted or spotted plus spinner dolphins; conversely, 59% of spotted dolphin and 96% of spotted plus spinner dolphin schools co-occurred with bird flocks. Most large schools of these dolphins were associated with birds, and thenumber and diversity of bird species increased with dolphin school size. The average species composition of birds in dolphin-associated flocks of northern tropical waters was: boobies 4 I.%, Wedge-tailed Shearwaters (Puffinus pacificus) 3 1.4%, jaegers 12.8%, Sooty Terns (Sterna firscata) 6%, frigatebirds 3.6%, and others 4.5%. Positive statistical associations were found among these bird species, which are explained by common attraction to food made available by feeding yellowfin tuna. In the southern latitudes and in the central Pacific, flocks were dominated by Sooty Terns, and few flocks were associated with dolphins. These flocks appeared to be associated with skipjack rather than yellowfin tuna.

Marks in Tooth Dentine of Female Dolphins (Genus Stenella) as Indicators of Parturition

In decalcified and hematoxylin-stained thin section, teeth of sexually mature female spotted dolphins (Stenella attenuata) often exhibit a deeply dark-stained layer (DSL) at the boundary of one or more of their annual growth layer groups. We compared DSL counts, made without reproductive information, to the corresponding reproductive condition in 75 females to test five hypotheses concerning the possible significance of DSLs. We found an exclusive association between DSLs and calving events. The teeth of an Hawaiian spinner dolphin, Stenella longirostris, labeled with tetracycline one month after giving birth to a calf in captivity, contained a dentinal DSL near the label. The number of DSLs in the dentine of a female probably indicates the minimum number of calves born to the female. In future studies DSL counts may be useful in estimating birth frequencies, year-specific birth rates, and calf mortality in odontocetes.

Movement and speed of dolphin schools responding to an approaching ship

Eight dolphin schools of the species Stenella attenuata. S. longk-ostris, and S. coeruleoalba were approached by ship and observed from a helicopter in the eastern Pacific to study their response to the vessel. All schools swam away from the projected track of the aproaching ship. Their movement, relative to the ship, followed paths that curved around the ship. Average swimming speeds while avoiding the ship varied from 5.1 to 8.8 knots. In some cases avoidance apparently began at 6 or more miles away from the ship. The effect of this behavior on shipboard censusingof dolphins is discussed. In the eastern tropical Pacific, tuna fishermen encircle with purse seine nets schools of certain small cetaceans, mainly spotted and spinner dolphins, Stenella attenuata and S. longirostris, to capture the yellowfin tuna, Thunnus albacares, with which they are associated (Perrin 1969, 1970). The resulting incidental kill of dolphins has led the National Marine Fisheries Service to study the status of these cetacean populations, as required by the Marine Mammal Protection Act of 1972. Data collected from commercial fishing boats and research vessels are important in determining the distribution and abundance of the dolphins. In the areas of intensive porpoise fishing, dolphins are apparently learning from their experience with nets and fishing vessels. The animals are recaptured with purse seines frequently enough to have possibly learned to position themselves within the net to better facilitate their own release (Pryor and Kang'). More importantly, they may also have developed various behaviors to avoid detection by a fishing vessel and to reduce their chances of capture (Pryor and Kang footnote 2; Stuntz and Perrin3). Dolphin schools, especially of the spotted and spinner dolphin species, commonly swim rapidly away from approaching ships. This behavior is

Body temperature and heat exchange in the hawaiian spinner dolphin, Stenella longirostris

1. 1. Deep body temperature, regional skin temperature and heat flow, and oxygen uptake were measured. 2. 2. In a free-swimming dolphin deep-body temperature ranged from 36.1–37.9° C (means 37.4, S.E. ± 0.03). 3. 3. There was considerable regional variability in the heat flow from the skin, being greatest from the distal parts of the extremities. 4. 4. Oxygen uptake was 1.5 times that of terrestrial mammals of comparable size. 5. 5. We conclude that these small tropical cetaceans live close to their lower critical temperatures, and depend upon the energy produced by activity, from solar radiation, and marked control over the peripheral insulation to maintain thermal balance.

Distribution and Differentiation of Populations of Dolphins of the Genus Stenella in the Eastern Tropical Pacific

There are at least two races of spotted dolphin, Stenella attenuata, in the eastern Pacific, based on length, color pattern, and skeletal differences. The coastal form is provisionally called S. attenuata graffmani. The offshore form is distinct from a third, Hawaiian race. Likewise, at least three unnamed races of spinner dolphin, S. longirostris, occur in the eastern Pacific. Length, shape of adult male, color pattern, and cranial differences are used to distinguish a Costa Rican, an eastern, and a whitebelly race. An Hawaiian race is distinct from these. A distributional break may indicate two stocks of the striped dolphin, S. coeruleoalba.

Fish Otoliths in Cetacean Stomachs and Their Importance in Interpreting Feeding Habits

The stomachs of 17 cetaceans of seven species (3 Kogia simus, 5 Stenella longirostris, 3 S. graffmani, 2 Lagenorhynchus obliquidens, 2 Delphinus delphis, 1 Lissodelphis borealis, and 1 Phocoena sinus) yielded 18,164 fish otoliths representing over 51 species, 40 genera, and 22 families. Lanternfish (family Myctophidae) otoliths accounted for more than 89% of the total, and they had come from at least 19 species belonging to nine genera. Only two fish species could have been identified if we had not been able to utilize otoliths. To be useful in food studies involving otoliths, cetacean stomachs cannot be placed in formalin solutions, even for short periods.The kinds and diversity of species preyed upon by several of these cetaceans indicate that they routinely forage in depths of 650–800 ft (200–250 m), and a few such as Kogia simus may descend to 1000 ft (300 m) or deeper.