Immature Dolphins Research Articles

Building Cetacean Locomotor Muscles Throughout Ontogeny to Support High Performance Swimming into Adulthood.

The demands on the locomotor muscles at birth are different for cetaceans than terrestrial mammals. Cetacean muscles do not need to support postural costs as the neonate transitions from the womb because water's buoyant force supports body weight. Rather, neonatal cetacean muscles must sustain locomotion under hypoxic conditions as the neonate accompanies its mother swimming underwater. Despite disparate demands at birth, cetaceans like terrestrial mammals require postnatal development to attain mature musculature. Neonatal cetaceans have a low proportion of muscle mass, and their locomotor muscles have lower mitochondrial density, myoglobin content (Mb) and buffering capacity than that found in the adult locomotor muscle. For example, the locomotor muscle of the neonatal bottlenose dolphin has only 10% and 65% of the Mb and buffering capacity, respectively, found in the adult locomotor muscle. The maturation period required to achieve mature Mb and buffering capacity in the locomotor muscle varies across cetacean species from 0.75-4 and 1.17-3.4 years, respectively. The truncated nursing interval of harbor porpoises and sub-ice travel of beluga whales may be drivers for faster muscle maturation in these species. Despite these postnatal changes in the locomotor muscle, ontogenetic changes in locomotor muscle fiber type seem to be rare in cetaceans. Regardless, the underdeveloped aerobic and anaerobic capacities of the locomotor muscle of immature dolphins results in diminished thrusting capability and swim performance. Size-specific stroke amplitudes (23-26% of body length) of 0-3-month-old dolphins are significantly smaller than those of >10·month-olds (29-30% of body length), and 0-1-month-olds only achieve 37% and 52% of the mean and maximum swim speed of adults, respectively. Until swim performance improves with muscle maturation, young cetaceans are precluded from achieving their pod's swim speeds, which could have demographic consequences when fleeing anthropogenic disturbances.

Cranial crassicaudiasis in two coastal dolphin species from South Africa is predominantly a disease of immature individuals.

Crassicauda spp. (Nematoda) infest the cranial sinuses of several odontocetes, causing diagnostic trabecular osteolytic lesions. We examined skulls of 77 Indian Ocean humpback dolphins Sousa plumbea and 69 Indo-Pacific bottlenose dolphins Tursiops aduncus, caught in bather-protecting nets off KwaZulu-Natal (KZN) from 1970-2017, and skulls of 6 S. plumbea stranded along the southern Cape coast in South Africa from 1963-2002. Prevalence of cranial crassicaudiasis was evaluated according to sex and cranial maturity. Overall, prevalence in S. plumbea and T. aduncus taken off KZN was 13 and 31.9%, respectively. Parasitosis variably affected 1 or more cranial bones (frontal, pterygoid, maxillary and sphenoid). No significant difference was found by gender for either species, allowing sexes to be pooled. However, there was a significant difference in lesion prevalence by age, with immature T. aduncus 4.6 times more likely affected than adults, while for S. plumbea, the difference was 6.5-fold. As severe osteolytic lesions are unlikely to heal without trace, we propose that infection is more likely to have a fatal outcome for immature dolphins, possibly because of incomplete bone development, lower immune competence in clearing parasites or an over-exuberant inflammatory response in concert with parasitic enzymatic erosion. Cranial osteolysis was not observed in mature males (18 S. plumbea, 21 T. aduncus), suggesting potential cohort-linked immune-mediated resistance to infestation. Crassicauda spp. may play a role in the natural mortality of S. plumbea and T. aduncus, but the pathogenesis and population level impact remain unknown.

Biphonal calls in Atlantic spotted dolphins (Stenella frontalis): bitonal and burst-pulse whistles

Biphonation, the simultaneous production of two sounds by a single animal, is found in the vocalizations of a range of mammalian species. Its prevalence suggests it plays an important role in acoustic communication. Concurrent vocal and behavioural recordings were made of Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas. The occurrence of two types of biphonal signals is reported: burst-pulse whistles with combined tonal and burst-pulse elements, and bitonal whistles. Biphonal whistles are rarely described in reports of dolphin acoustic repertoires, but were common in these dolphins: of all whistles analysed (n = 1211), 26.84% were burst-pulse whistles and 4.71% were bitonal whistles. A subset of whistles (n = 397) were attributed to dolphins of specific age classes, and used to compare prevalence of biphonation across age. Biphonation occurred in 61.54% of sexually mature and 48.32% of sexually immature dolphins’ whistles. Sexually immature dolphins emitted more burst-pulse whistles than older dolphins: 44.13% of sexually immature dolphins’ whistles were burst-pulse whistles, while 15.38% of adult whistles were burst-pulse whistles. Bitonal whistle production was more prevalent in sexually mature dolphins: 41.03% of adult whistles were bitonal, while only 4.19% of sexually immature dolphins’ whistles were bitonal. The prevalence of a biphonal component in specific repeated, stereotyped whistle contours suggests that these acoustic features could be important components of contact calls, or signature whistles. The biphonal components of spotted dolphin whistles may serve to convey additional information as to identity, age or other factors to conspecifics.

Diet of long-beaked common dolphin (Delphinus capensis) in the East Sea, Korea

The long-beaked common dolphin is one of the most abundant cetaceans in Korean waters, and their population has been estimated to comprise of more than 35,000 individuals. Delphinus capensis generally appear close to the coast and primarily feed on epipelagic small fishes and cephalopods. Thirty long-beaked common dolphins were collected from the East Sea from February to September in 2012. For stomach content analysis (SCA), the fresh prey items were identified to their lowest taxonomic level, and unidentified preys due to digestion were identified using remnants such as fish otoliths and cephalopod beaks. Fatty acid (FA) patterns of 20 dolphins from the inner layer of blubber were compared with those in samples of prey items. Enoploteuthis chunii was the dominant prey in SCA, representing 55.8% by number and 75.9% by occurrence. Common squid (Todarodes pacificus) and Pacific herring (Clupea pallasii) were the next major preys at more than 80% occurrence. Even though a distinctive difference was not observed between genders, there was a significant diet variation related to maturity. Immature dolphins consumed a higher diversity of prey, and consumed more equally than the sexually mature group, who showed a high dominance of cephalopods. Furthermore, this result fairly corresponded to FAs composition of mature dolphins with the raised percent of 20:6n–3, which is relatively abundant in T. pacificus.

Ontogenetic development and sexual dimorphism of franciscana dolphin skull: A 3D geometric morphometric approach.

The aim of this work was to study the postnatal ontogenetic development of Pontoporia blainvillei skull, identifying major changes on shape, and relating them to relevant factors in the life history of the species. We analyzed a complete ontogenetic series (73♂, 83♀) with three-dimensional geometric morphometric techniques. Immature dolphins showed a very well-developed braincase and a poorly developed rostrum, and the principal postnatal changes affected the rostrum and the temporal fossa, both structures implied functionally to the feeding apparatus, thus suggesting a specialized mode for catch fast prey in P. blainvillei. Osseous elements associated with sound production were already well developed on immature dolphins, suggesting the importance of this apparatus since the beginning of postnatal life. Sexual dimorphism was detected on both shape and size variables. Females were bigger than males, in accordance with previous studies. Shape differences between sexes were found on the posterior part of premaxillaries and external bony nares (P < 0.01), suggesting that this sexual dimorphism is related to differences on vocalization capabilities.

Biological parameters of franciscana dolphins,Pontoporia blainvillei, by-caught in artisanal fisheries off southern Buenos Aires, Argentina

The franciscana dolphin (Pontoporia blainvillei) is a small coastal dolphin endemic to the south-western Atlantic Ocean. Incidental captures in fishing gillnets is possibly the greatest conservation concern for this species, and occurs within most of its geographical distribution. The aim of this paper is to determine the biological parameters of franciscana dolphin by-caught from artisanal coastal fisheries of the southern Buenos Aires province, Argentina. Between 2003 and 2009, carcasses of 54 incidentally captured franciscanas were collected. The age, sexual and physical maturity and body condition of each specimen was determined. The sex-ratio of the by-caught dolphins did not differ from parity and, consistent with other areas, juveniles younger than 4 yr old were captured in higher proportion (69%). In addition, 74% of the entangled animals were sexually immature and 85% physically immature. Sexually immature dolphins were predominant in the spring, a period which coincides with the breeding season. An assessment of the body condition of captured franciscanas suggests that entanglements were not associated with a disease or physiological disorder. The results presented here are important to assess the impact of artisanal fisheries on the population of franciscana dolphins in the southernmost area of its distribution.

Ultrasonographic assessment of the thyroid gland and adjacent anatomic structures in Indo-Pacific bottlenose dolphins (Tursiops aduncus)

To evaluate the use of ultrasonography for thyroid gland assessment in healthy Indo-Pacific bottlenose dolphins (Tursiops aduncus), describe the ultrasonographic appearance of the thyroid gland and adjacent anatomic structures, and identify potential associations between variations in thyroid gland morphology and demographic features in this species. 18 captive Indo-Pacific bottlenose dolphins. 1,404 ultrasonographic examinations of the thyroid gland and adjacent anatomic structures (eg, cervical lymph nodes, musculature, and vasculature) were performed during the > 3-year study period. Shape, echogenicity, and homogeneity of thyroid glands were assessed, and glands were categorized into morphological configurations on the basis of results of 2-D and 3-D ultrasonographic evaluation. Associations between demographic factors and thyroid gland morphology were assessed. Thyroid lobes appeared elliptical or fusiform in the transverse scan plane and round to oval in longitudinal scan planes; morphologically, glands comprised 2 lobes joined by an isthmus or a roughly diamond-shaped structure located on the ventral surface of the trachea. Major blood vessels and cervical lymph nodes were identified. Thyroid parenchyma was typically uniform and homogeneous, with echogenic reticulations and well-defined borders. Thyroid glands were hypoechoic or isoechoic relative to the sternocephalicus muscle; echogenicity was greater in adolescents than in adults. Thyroid gland volume differed between sexes, between sexually mature and immature dolphins, and among age groups and was positively correlated with body length and weight. Ultrasonography provided a reliable and repeatable method for evaluation of thyroid glands and adjacent anatomic structures in live dolphins.

Genetic and family structure in a group of 165 common bottlenose dolphins caught off the Japanese coast

AbstractThe biological and genetic structure of common bottlenose dolphins (Tursiops truncatus) that migrate seasonally near Japan remains largely unknown. We investigated the genetic and family structure in a group of 165 common bottlenose dolphins caught off the coast of Japan using mitochondrial DNA (mtDNA) and 20 microsatellite DNA markers. Phylogenetic analysis of the mtDNA control region sequences suggested that the dolphins were related more closely to oceanic types from Chinese waters than other geographic regions. The information on sex, sexual maturation and age together with the genetic markers revealed a strong likelihood for 37 familial relationships related mostly to maternity and an under‐representation of juvenile female offspring. The maternal dolphins had a similar offspring‐birth interval as the coastal types from North Atlantic Ocean, but a slightly younger first‐progeny age. The sex bias in the captured group was particularly marked towards an over‐representation of males among the young and immature dolphins, whereas the mature adults had an equal number of males and females. These results should be useful for future comparative biological, genetic and evolutionary investigations of bottlenose dolphins from the North Pacific Ocean with those from other regions.

PAPILLOMAVIRUS ANTIBODY PREVALENCE IN FREE-RANGING AND CAPTIVE BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS)

Genital epithelial tumors of Atlantic bottlenose dolphins (Tursiops truncatus [Tt]) and Burmeister's porpoises (Phocoena spinipinnis) were formerly shown to be associated with papillomavirus (PV) infection. Papillomaviruses are highly prevalent viruses involved in the development of various tumor types in a wide range of animals, and so-called high-risk PVs contribute to malignant progression. In marine mammals, the incidence and prevalence of PV infection, transmission pathways, and persistence of infection are largely unknown. Using virus-like particles of bottlenose dolphin PV type 1 (TtPV1) as the antigen, enzyme-linked immunosorbent assay (ELISA) studies were conducted to evaluate PV antibody prevalence in bottlenose dolphins. In total, sera obtained from 115 dolphins were examined. Fifty-one percent of captive dolphins (n=18 of 35) and 90% of free-ranging dolphins (n=72 of 80) were antibody positive. Higher ELISA reactivity was observed among males compared with females. Sexually immature dolphins appeared more likely to seroconvert with age. Besides determining their PV antibody prevalence, each animal was also assessed for the presence of orogenital tumors. Interestingly, the mean age of free-ranging dolphins with tumors (n=21) was 11.2 yr compared with 29.9 yr in captive dolphins with tumors (n=9). Results from the current study suggest PV infection in bottlenose dolphins is common, that the main route of PV transmission among them may be horizontal, and that orogenital neoplasia may develop in early life stages of certain free-ranging bottlenose dolphins.

Distribution and Population Demographics of Common Dolphins (&lt;I&gt;Delphinus delphis&lt;/I&gt;) in the Gulf St. Vincent, South Australia

Within Australian waters, short-beaked common dolphins (Delphinus delphis) are exposed to a vari-ety of human-induced impacts, including aquacul-ture and fisheries. Nonetheless, the occurrence and distribution of common dolphins within these waters remains unknown. Data detailed herein represent the first report of the occurrence and distribution of common dolphins from Australian waters. The density and relative abundance of common dolphins within Gulf St. Vincent (GSV), South Australia, was examined between September 2005 and May 2008 using systematic boat surveys. During 1,850 km of survey effort, a total of 108 independent groups, involving 564 common dolphins, were observed. Group size ranged from 2 to 21 individuals (mean = 5.26, SD = 3.687), with immature dolphins found in larger group sizes. Adults were the most frequent age class observed in this population (60.3%, n = 340), with neonates and calves observed most frequently between December and April. Sighting frequency was 3 groups/100 km² travelled, with an encounter rate of 16 common dolphins/100 km². The western longitude and southern latitude sections of GSV were used most frequently by this species, with most groups recorded in water depths of 35 to 40 m (mean = 37.2 m, SD = 1.4), and in areas 21 to 31 km from land (mean = 27.4 km, SD = 2.6). Common dolphin density was estimated to be 0.5 dolphins/100 km2, with a population estimate of 1,957 dolphins within their preferred habitat (waters deeper than 14 m). Results suggest the GSV is important for this spe-cies and that common dolphins use these waters as a nursery area.

PHYSIOLOGICAL AND BEHAVIORAL DEVELOPMENT IN DELPHINID CALVES: IMPLICATIONS FOR CALF SEPARATION AND MORTALITY DUE TO TUNA PURSE‐SEINE SETS

AbstractTuna 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.

Feeding ecology of the Indo-Pacific bottlenose dolphin ( Tursiops aduncus) incidentally caught in the gillnet fisheries off Zanzibar, Tanzania

The stomach contents of 26 Indo-Pacific bottlenose dolphins ( Tursiops aduncus) incidentally caught in gillnet fisheries around Unguja Island (Zanzibar) between February 2000 and August 2002 were examined. The relative importance of each prey species was assessed through indices of relative importance. In total, 1403 prey items comprising 50 species of bony fish and three species of squid were identified from food remains. Five species of fish, Uroconger lepturus, Synaphobranchus kaupii, Apogon apogonides, Lethrinus crocineus, Lutjanus fulvus, and three species of squid, Sepioteuthis lessoniana, Sepia latimanus and Loligo duvauceli, were the most important prey species. Based on an index that included frequency of occurrence, percentage by number and by weight, Uroconger lepturus proved to be the most important prey species of mature dolphins whereas Apogon apogonides was the preferred prey of immature dolphins. These results indicate that Indo-Pacific bottlenose dolphins off the coast of Zanzibar forage on a relatively large number of prey species, but that only a few small- and medium-sized neritic fish and cephalopods contribute substantially to the diet. Further, the ecology and behavior of the preferred fish prey species indicate that the dolphins forage over reef or soft bottom substrata and near the shore.

The development of blood oxygen stores in bottlenose dolphins (Tursiops truncatus): implications for diving capacity

AbstractEnhanced oxygen reserves in the blood facilitate diving in marine mammals. For pinnipeds (seals and sea lions), a developmental period of 4 to 24 months is required for blood oxygen stores to reach adult capacities. We investigated whether a similar developmental period for the blood occurs in cetaceans (dolphins and whales), a group of mammals that are exposed to diving immediately after birth. Blood samples were collected from wild and zoological park bottlenose dolphins Tursiops truncatus aged 0–12 years. Red blood cell number (RBC), haemoglobin content (Hb), haematocrit (Hct), mean corpuscular volume (MCV), mean cell haemoglobin (MCH), and mean corpuscular haemoglobin concentration (MCHC) were determined for each sample. We found that during postnatal development, RBC, Hb and Hct decreased from 0 to 1.5 months and then increased from 1.5 to 6 months, reaching adult levels by 3 years. MCV and MCH both increased from birth. MCHC decreased from 0 to 3.2 months and then increased. Adult levels for MCV were attained as early as 2 months of age while adult levels for MCH and MCHC were attained by 6 months of age. These results indicate that, for bottlenose dolphins, the development of the blood and its capacity to store oxygen is not complete with weaning, which generally occurs at 1.5 years old. The lower oxygen storage capacity of immature dolphins is likely to limit dive capabilities. Calculated aerobic dive limits (cADLs) for 0‐ to 2‐year‐old dolphin calves are 1.9–3.6 min, compared to 4.8–5.4 min for 3‐ to 12‐year‐old dolphins. Increases in cADLs from 0 to 3 years are attributed to increases in both body mass and mass specific oxygen stores while body mass alone explains the increases in cADLs from 3 to 9 years. The limited diving capacity of young dolphins may influence the foraging behaviours of newly weaned juveniles and females accompanied by calves.

Organochlorine, organobromine, metal, and selenium residues in bottlenose dolphins (Tursiops truncatus) collected during an unusual mortality event in the Gulf of Mexico, 1990.

Polychlorinated biphenyls (PCBs), cis-chlordane, oxychlordane, heptachlor epoxide, mirex, hexachlorobenzene (HCB), lindane, octachlorostyrene (OCS), p,p'-DDE,p,p'-DDT, dieldrin, triphenylphosphate (TPP), polybrominated biphenyls (PBBs), and polybrominated diphenyl ethers (PB-DPEs) were measured in the blubber, and five metals (mercury, lead, cadmium, chromium, and manganese) and selenium were measured in the liver of bottlenose dolphins (Tursiops truncatus) obtained from the Gulf of Mexico during an unusual mortality event in 1990. The collection of animals included fetuses, sucklings (< 1 year old), immature dolphins (2-5 years old), and adults of both sexes. PCBs, p,p'-DDE, HCB, and PBDPEs were detected in the blubber of each animal. Mean concentrations of organic contaminants were generally highest in adult males. p,p'-DDE was the single component analyte measured at the highest concentration. Immature females had greater concentrations of most chlorinated organics than adult females. Mercury and cadmium concentrations in liver increased with increasing age-class. The correlation between mercury and selenium in all animals was r = 0.96, with a mole ratio of 0.90. Concentrations of lead, manganese, cadmium, and chromium did not follow any particular age-class trend.

Mercury and Selenium Levels in Striped Dolphins Caught off the Pacific Coast of Japan

We examined the distribution of mercury and selenium in fifteen tissues of striped dolphins (Stenella coeruleoalbd). The total mercury level in the mature dolphins showed differences among the tissues and was highest in the liver. The total mercury concentration in most tissues increased with age, and reached a constant level at 20 to 25 years of age. The total mercury level in the tissues was not appreciably different among mature males, pregnant females, lactating females and resting females. In the muscle of mature individuals, the total mercury level of striped dolphins collected in 1977 and 1980 was appreciably higher than that of those collected 1978 and 1979. Methylmercury showed less variation in concentration among the tissues. The ratio of methylmercury to total mercury in muscle decreased with growth after about 10 years of age when the increase of methylmercury stopped. Selenium levels in the dolphins increased with age as total mercury levels did. High correlation coefficients were found between the total mercury and selenium levels in spleen, muscle, pancreas and liver. The concentrations of total mercury in the various tissues of immature dolphins were much lower than those of mature ones.