Spotted Dolphin Research Articles

Imitation of Computer-Generated Sounds by Wild Atlantic Spotted Dolphins (Stenella frontalis)

Since 1985 a community of wild Atlantic spotted dolphin (Stenella frontalis) have been observed underwater in the Bahamas. A human-worn, acoustic underwater two-way communication interface was developed and deployed from 2013-2016. Dolphins were exposed to an acoustic referentially based wearable underwater computer/interface. A model/rival system was used with dolphins and human participants during in-water sessions. Artificial and natural objects were labeled with computer generated sounds. Female juvenile spotted dolphins dominated the activity. Group size averaged seven dolphins for an average duration of 37 minute over 58 sessions. Of 243 video audio imitations and 56 Cetacean Hearing Augmentation Telemetry (CHAT) audio imitations, six potential response types were documented and measured. Stand-alone vocal contour mimics and Frequency Modulated Contours were the most common imitations. Within 5 sec of a computer-generated sound playing, of the 191 non-stand-alone vocal responses that were produced, 114 of them (59.7%) were judged as partial accurate matches, 3 of them (1.57%) were judged as non-matching partial imitations of a computer-generated sound, 67 of them (35.08%) were signature whistles, and seven of them (3.67%) were either non-signature whistle vocalizations or a mimic of the start or end tones. Thus, the majority of vocalizations produced by the dolphins within five seconds of a computer-generated sound were partial accurate imitations for the computer-generated sound played. Dolphins demonstrated both immediate and delayed vocal imitation and flexible attempts at imitation but did not show signs of a functional understanding of object labels. Atlantic spotted dolphins showed vocal flexibility in reaction to humans broadcasting computer generated sounds.

Drones Assist in the First Report of a Mixed-Species Group of Tursiops truncatus (Common Bottlenose Dolphin) and a Stenella frontalis (Atlantic Spotted Dolphin) along the Southeast Florida Coast

Drones Assist in the First Report of a Mixed-Species Group of Tursiops truncatus (Common Bottlenose Dolphin) and a Stenella frontalis (Atlantic Spotted Dolphin) along the Southeast Florida Coast

Understanding Trophic Transference Role in Mercury Biomagnification and Bioaccumulation in the Atlantic Spotted Dolphin (Stenella Frontalis)

Understanding Trophic Transference Role in Mercury Biomagnification and Bioaccumulation in the Atlantic Spotted Dolphin (Stenella Frontalis)

Mapping the Exposure of Pantropical Spotted Dolphins and Common Bottlenose Dolphins to Different Categories of Vessel Traffic in Maui Nui, Hawai‘i

The increase and diversification of vessel traffic worldwide has resulted in a variety of known disturbances to dolphins. As a remote island chain, the Hawaiian Islands rely heavily on the marine environment for transportation, recreation, and fishing that aggregates into significant levels of vessel traffic. Given the known presence of dolphins in this region, there is a gap in knowledge regarding the relative exposure risk that vessel traffic poses to island-associated dolphin populations in Hawai‘i. This research identified the spatial distribution of pantropical spotted dolphins (Stenella attenuata) and common bottlenose dolphins (Tursiops truncatus) and determined the extent of their overlap with various categories of vessel traffic in Maui Nui, Hawai‘i. Species distribution was determined using kernel density estimates based on sighting data from 50 spotted dolphin sightings and 75 bottlenose dolphin sightings collected from 2013 to 2018. A combination of vessel GPS and Automatic Identification Systems (AIS) vessel tracks were used to quantify vessel traffic within the study area, resulting in 22,464 vessel tracks that were subsequently compiled into categories for analysis from 2014 to 2017. Risk of vessel exposure between vessels and dolphins, or co-occurrence, was determined by calculating the product of predicted dolphin density and predicted vessel density. Both species were exposed to vessel traffic risk over 100% of their distribution, but their highest exposure risk varied spatially, with high risk defined as > 0.25 on a normalized scale of low (0) to high (1) risk. The highest vessel exposure risk for spotted dolphins occurred in deeper, offshore waters, while the highest risk for bottlenose dolphins was in shallow, coastal waters. The vessel categories with the largest area of high risk to spotted dolphins were tour vessel and commercial fishing vessel traffic, while commercial transportation traffic had the highest exposure risk for bottlenose dolphins. This article provides baseline information for understanding the vulnerability of two island-associated dolphin populations to the threat of vessel traffic and highlights the differences in relative exposure risk based on species and vessel categories.

External Scarring as an Indicator of Fisheries Interactions with Bottlenose (Tursiops truncatus) and Pantropical Spotted (Stenella attenuata) Dolphins in Maui Nui, Hawai‘i

External Scarring as an Indicator of Fisheries Interactions with Bottlenose (Tursiops truncatus) and Pantropical Spotted (Stenella attenuata) Dolphins in Maui Nui, Hawai‘i

First Observation of Pregnancy and Parturition in a Captive Pantropical Spotted Dolphin (Stenella attenuata)

A female pantropical spotted dolphin (Stenella attenuata) successfully mated with a mature male in captivity on April 13, 2017. This mating event was followed by an evaluation of the plasma progesterone concentration, appetite, and rectum temperature of the dolphin during pregnancy. We recorded the progesterone profiles during pregnancy, the gestation period, and the parturition events. The progesterone level (ng/mL) ranged between 0.7 and 133.4 (n = 27), and the average was 45.1 (SD = 38.5). Immediately after mating, extremely high progesterone levels were observed, which showed a decreasing trend towards the parturition day. The gestation period was 352 days. On the morning of the parturition day on March 31, the female displayed symptoms such as a drop in rectal temperature by approximately 1°C and reduced appetite. The time from the first observation of vaginal discharge to the fluke's appearance was 5.5 hr, while the subsequent period until birth was 4 hr in length. The time from parturition to the first successful nursing was approximately 4 hr, while the time from the nursing to the placental passage was less than 1 hr. To the best of our knowledge, this is the first report on the pregnancy period of pantropical spotted dolphins in captivity.

Exploration of Horizontal Information Transmission through Social Learning in Juvenile Atlantic Spotted Dolphins (Stenella frontalis)

Exploration of Horizontal Information Transmission through Social Learning in Juvenile Atlantic Spotted Dolphins (Stenella frontalis)

Effects of Enrichment Presentation and Other Factors on Behavioral Welfare of Pantropical Spotted Dolphin (Stenella attenuata)

ABSTRACTEnvironmental enrichment is a crucial element of promoting welfare for animals in captivity. However, enrichment programs are not always formally evaluated for their efficacy. Furthermore, there is little empirical evidence of enrichment evaluation for species of small cetaceans in zoological settings. A wide range of variables may potentially influence enrichment efficacy and how it in turn affects behavior. The purpose of this study was to determine the most preferred environmental enrichment, and method of presentation, for a species that has not been well studied in captivity, the pantropical spotted dolphin (Stenella attenuata). In order to determine which enrichment items and method of presentation were most effective at eliciting enrichment interaction, we systematically examined how several variables of enrichment influenced enrichment interaction. The results suggested that presenting enrichment after training sessions influenced interaction with the enrichment. The results also indicated preference for enrichment type and a specific enrichment device. Finally, factors that influenced interaction were also found to influence aberrant behavior. The results support the premise that enrichment be “redefined” for each species and each individual.

Whistle Acoustic Parameters in Atlantic Spotted Dolphins (Stenella frontalis) and Bottlenose Dolphins (Tursiops truncatus) in Two Locations in The Bahamas and Comparisons with Other Populations

Whistle Acoustic Parameters in Atlantic Spotted Dolphins (Stenella frontalis) and Bottlenose Dolphins (Tursiops truncatus) in Two Locations in The Bahamas and Comparisons with Other Populations

Using Genome-Wide SNPs to Detect Structure in High-Diversity and Low-Divergence Populations of Severely Impacted Eastern Tropical Pacific Spinner (Stenella longirostris) and Pantropical Spotted Dolphins (S. attenuata)

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 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.

Mother-Offspring Signature Whistle Similarity and Patterns of Association in Atlantic Spotted Dolphins (Stenella frontalis)

We assessed the degree of similarity between signature whistles of mother and offspring pairs in free- living Atlantic spotted (Stenella frontalis). As a means of qualitative evaluation, judges compared the time- frequency contour patterns of signature whistle spectrograms. We also evaluated quantitative measurements of whistle frequency and duration. All five female offspring produced signature whistles that were similar to their whistles by a least one means of comparison, whereas two of the four male offspring produced signature whistles that were dissimilar from their by both methods of comparison. However, statistically, male offspring were just as likely to produce signature whistles like their as female offspring (p = 0.167). We compared whistle similarity between mothers and offspring to the degree of association for each pair. Offspring that most often associated with their mothers when they were four years of age had whistles that were more similar to their whistles both qualitatively (r(4) = 0.92, p = 0.009) and quantitatively (r(4) = 0.92, p = 0.004). Because signature whistles are developed within a dolphins first year, our finding likely reflects the level of bond between mother and calf.

High-grade Astrocytoma (Glioblastoma Multiforme) in an Atlantic Spotted Dolphin (Stenella frontalis)

This report describes the gross, microscopical and immunohistochemical features of a high-grade astrocytoma (glioblastoma multiforme) in an adult male Atlantic spotted dolphin (Stenella frontalis). On necropsy examination, a 5 × 2.5 × 2 cm, poorly demarcated, red, friable and locally expansile mass effaced the thalamus and the left periventricular region and extended to the left lateral ventricle of the brain. Microscopically, the mass consisted of haphazardly arranged bundles and rows of interweaving polygonal to spindle-shaped cells. These often palisaded along serpentine foci of necrosis and were surrounded by prominent vessels. Immunohistochemically, the neoplastic cells expressed glial fibrillary acidic protein, but not vimentin, S100 protein, neuron-specific enolase or neurofilament protein. A diagnosis of high-grade astrocytoma was made and this represents the first description of a glioma in a cetacean species.

Primary Uterine T-cell Lymphoma with Metastasis in an Atlantic Spotted Dolphin (Stenella frontalis), Canary Islands, Spain

We describe gross, histopathologic, and immunonocytologic features of a primary uterine T-cell lymphoma with multiple metastases in an adult female Atlantic spotted dolphin (Stenella frontalis). Neoplastic T-cell lymphocytes (CD3+) partially effaced the uterus, ovaries, mesosalpinx, and urinary bladder and variably infiltrated abdominal and thoracic organs. Herpesvirus and morbillivirus PCR were negative.

Directionality of Sexual Activities During Mixed-Species Encounters between Atlantic Spotted Dolphins (Stenella frontalis) and Bottlenose Dolphins (Tursiops truncatus)

In the Bahamas, interspecific groups of Atlantic spotted dolphins, Stenella frontalis, and bottlenose dolphins, Tursiops truncatus, have been observed underwater since 1985 on Little Bahama Bank. Mixed-species groups engage in associative behaviors and aggression on a regular basis. Because of their complex cognitive behaviors and large brain encephalization, dolphins are likely capable of complex social interactions, even between species.Between 1993-2003, 177 Mixed-Species Encounters (MSE) were categorized by the age class of male spotted dolphins, the ratio of spotted dolphins to bottlenose dolphins, behavior as Associative (traveling, babysitting, play) or Aggressive (chases, mounting, head to heads) and by directionality of sexual behavior. The majority (68%) of MSE involved adult spotted dolphin. Associative behaviors were observed more than aggressive behaviors in groups where no adult male spotted dolphin, only male calves, or male juvenile spotted dolphins were present. Aggressive behaviors were observed more frequently than associative behaviors in adult male spotted dolphin groups. When groups were unbalanced in favor of one species or the other, differences in social interactions occurred. Male spotted dolphins were never observed attempting to mount male bottlenose dolphin although they chased them. Despite the larger ratio of male spotted dolphins to bottlenose dolphins during MSE, directionality of male-to-male sexual contact was primarily one-way. Male bottlenose dolphin mounted and copulated with male spotted dolphins but not the reverse. Opportunities for cross-species mating and hybridization clearly occurred. Male bottlenose dolphins copulated with female spotted dolphins and male spotted dolphins copulated with female bottlenose dolphins. These sympatric dolphins in the Bahamas have a complex and dynamic relationship that varies with sex and age and revolves around potential reproductive isolation issues.

Underwater Mirror Exposure to Free-Ranging Naïve Atlantic Spotted Dolphins (Stenella frontalis) in the Bahamas

The “mirror state,” described for human self-recognition, has been found in captive or human-raised species. In marine mammals, bottlenose dolphins and killer whales have shown evidence of body examination, self-directed and contingency checking behaviors whereas false killer whales appeared ambiguous and California sea lions did not recognize themselves in a mirror. Self-recognition processes in wild cetaceans remain unknown. Since 1985, a resident community of Atlantic spotted dolphin (Stenella frontalis) has been studied underwater in the Bahamas. We describe the reaction of free-ranging dolphins during 14 exposures to the presence of a mirror from 1994/1995 and 2004/2005. Responses to the mirror were mixed. Initial reactions of mother/calf groups were to swim around mirror and stay in close physical proximity. Others ignored the mirror entirely, or swam around or underneath. A single male became stationary and postured in an aggressive stance in front of the mirror. The wild spotted dolphins showed a significant preference to exposing and/or orienting their right side to the mirror versus their left side. We suggest that the animals assign different meanings to a mirror in the wild versus the same object in captivity.

Development of the Skull of the Pantropical Spotted Dolphin (Stenella attenuata)

We describe the bony and cartilaginous structures of five fetal skulls of Stenella attenuata (pantropical spotted dolphin) specimens. The specimens represent early fetal life as suggested by the presence of rostral tactile hairs and the beginnings of skin pigmentation. These specimens exhibit the developmental order of ossification of the intramembranous and endochondral elements of the cranium as well as the functional and morphological development of specific cetacean anatomical adaptations. Detailed observations are presented on telescoping, nasal anatomy, and middle ear anatomy. The development of the middle ear ossicles, ectotympanic bone, and median nasal cartilage is of interest because in the adult these structures are morphologically different from those in land mammals. We follow specific cetacean morphological characteristics through fetal development to provide insight into the form and function of the cetacean body plan. Combining these data with fossil evidence, it is possible to overlie ontogenetic patterns and discern evolutionary patterns of the cetacean skull.

Detection of Helicobacter in the Digestive Tract of an Atlantic Spotted Dolphin (Stenella frontalis)

Helicobacter spp. occur in the digestive system of a broad range of animal taxa, including marine mammals. Only one formally recognized species, Helicobacter cetorum, has been described in marine mammals. Helicobacter has not been reported in the Atlantic spotted dolphin (Stenella frontalis). The purpose of our study was to examine the digestive tract of a stranded spotted dolphin for Helicobacter. Tissue and content samples were collected at necropsy and examined by histopathology and molecular analyses using Helicobacter genus-specific 16S rDNA polymerase chain reaction (PCR) and DNA sequencing. Helicobacter was detected in all stomach divisions and the duodenal ampulla. A sequence type of the 16S rRNA gene shared a 98-99% identity to sequences from H. cetorum. This study reports for the first time Helicobacter in S. frontalis.

Cranial Variation in the Pantropical Spotted Dolphin, Stenella attenuata, in the Pacific Ocean

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.

A Bayesian integrated population dynamics model to analyze data for protected species

Managing wildlife-human interactions demands reliable information about the likely consequences of management actions. This requirement is a general one, whatever the taxonomic group. We describe a method for estimating population dynamics and decision analysis that is generally applicable, extremely flexible, uses data efficiently, and gives answers in a useful format. Our case study involves bycatch of a protected species, the Northeastern Offshore Spotted Dolphin (Stenella attenuata), in the tuna fishery of the eastern Pacific Ocean. Informed decision-making requires quantitative analyses taking all relevant information into account, assessing how bycatch affects these species and how regulations affect the fisheries, and describing the uncertainty in analyses. Bayesian analysis is an ideal framework for delivering information on uncertainty to the decision-making process. It also allows information from other populations or species or expert judgment to be included in the analysis, if appropriate. Integrated analysis attempts to include all relevant data for a population into one analysis by combining analyses, sharing parameters, and simultaneously estimating all parameters, using a combined objective function. It ensures that model assumptions and parameter estimates are consistent throughout the analysis, that uncertainty is propagated through the analysis, and that the correlations among parameters are preserved. Perhaps the most important aspect of integrated analysis is the way it both enables and forces consideration of the system as a whole, so that inconsistencies can be observed and resolved.

Distribution, Habitat Partitioning, and Abundance of Atlantic Spotted Dolphins, Bottlenose Dolphins, and Loggerhead Sea Turtles on the Eastern Gulf of Mexico Continental Shelf

We surveyed cetaceans and marine turtles from Nov. 1998 to Nov. 2000 along a series of prescribed transects between Tampa Bay and Charlotte Harbor, Florida, and between the coast and the 180-m isobath. Vertical profiles of temperature, salinity, and chlorophyll concentration were collected at 65 stations, and continuous surface data on these variables and transmittance were collected while underway. Habitat partitioning among Atlantic spotted dolphins (Stenella frontalis), bottlenose dolphins (Tursiops truncatus), and loggerhead sea turtles (Caretta caretta) was examined by canonical correspondence analyses of environmental characteristics at sighting locations. Environmental characteristics and primary productivity of S. frontalis and T. truncatus habitat on the eastern Gulf of Mexico continental shelf significantly differed. In shelf waters shallower than 20 m, T. truncatus were the dominant cetacean species, whereas S. frontalis were the most common shelf species at depths of 20-180 m. Environmental preferences of C. caretta were intermediate between the two dolphin species and showed no apparent relationship with depth. The continental shelf in the eastern Gulf of Mexico is broad, with distances from coast to slope as great as 200 km. Although S. frontalis habitat has elsewhere been described as ubiquitous over the shelf, our data suggest that S. frontalis in the eastern Gulf of Mexico prefer midshelf habitat.