Dolphin Species Research Articles

Spatial and temporal separation of toothed whales in the western North Atlantic

A diverse group of toothed whale species inhabits the pelagic habitats of the western North Atlantic, competing for overlapping prey resources. Historical data deficits have limited fundamental research into many of these species, such as establishing baselines of distribution and abundance, so their occurrence and habitat use patterns are not well characterized. Periodic cycles in activity have been reported at a range of temporal scales for odontocetes in other regions, such as seasonal movements, foraging activity modulated by lunar cycles, and diel activity patterns. A variety of spatial, temporal, and behavioral separation strategies have also been observed among predator guilds in both marine and terrestrial systems, and these may also contribute to observed spatiotemporal patterns in activity. Recently, passive acoustic data has been applied to monitor odontocete species continuously, with improved detection and species discrimination for some cryptic species. We used a long-term passive acoustic data set collected at sites spanning the western North Atlantic shelf-break region to quantify presence and characterize seasonal, lunar, and diel activity patterns for 10 species. Our results demonstrated strong regional preferences and clear patterns of spatiotemporal separation between species with similar foraging ecology. Latitudinal shifts in seasonal presence peaks may suggest meridional seasonal migrations for some dolphin species. We also observed strong diel activity patterns that were modulated by both seasonal and lunar cycles. This study reveals complex behavioral patterns arising in response to natural cycles playing out over multiple temporal scales and provides new insights into habitat partitioning among toothed whale species.

Identifying the hotspot area of Indo-Pacific humpback (Sousa chinensis) and Irrawaddy (Orcaella brevirostris) dolphins in Matang waters, Perak, Malaysia

Abstract. Sobri MF, Jaaman SA, Mohamed Z, Muda AM, Rashid MASA, Zhang X. 2022. Identifying the hotspot area of Indo Pacific humpback (Sousa chinensis) and Irrawaddy (Orcaella brevirostris) dolphins in Matang waters, Perak, Malaysia. Biodiversitas 23: 6106-6113. The Indo-Pacific humpback (Sousa chinensis) and Irrawaddy (Orcaella brevirostris) dolphins are commonly found in Matang waters, Perak, Malaysia. The area, filled with healthy mangrove forest cover and many estuaries, is not only frequented by the dolphins for its daily activities but also extensively used by locals for artisanal fishing, charcoal production and organizing ecotourism activities. There could be a high risk of human-dolphin interactions, hence determining habitat use and identifying critical habitats or "hot spots" for the dolphins in the area is important. In this study, a series of dedicated boat sighting surveys were conducted from March 2019 to January 2021 between Kuala Gula and Kuala Jarum Mas. The total survey effort was 3325.76 km, 44 days and 239.38 hours. A total of 69 dolphin sightings were made, consisting of 40 Indo-Pacific humpback dolphins and 29 Irrawaddy dolphin observations, respectively. During each sighting, every dolphin's behaviors were categorized as: foraging, socializing, evasive, and travelling, and the survey area was classified into four blocks. The results indicated that different dolphin species have different hotspot areas. For Indo-Pacific humpback dolphins, the hotspot area was Kuala Sangga, while the Irrawaddy dolphin's hotspot area was outside Kuala Larut, and there was a small overlap between the two dolphins' hotspots. Among the recorded behaviors (n: 281) for both dolphins, the most dominant was foraging (72.24%), followed by socializing (17%), evasive (7%), and travelling (4%). The sighted foraging behavior for both dolphin populations was dominant, indicating the hot spots were major foraging grounds for the two dolphin populations. This study shows the importance of Matang waters as a conservation area for the species and warrants further studies of dolphin population ecology to be conducted.

Alzheimer's disease-like neuropathology in three species of oceanic dolphin.

Alzheimer's disease (AD) is the most common neurodegenerative disease and the primary cause of disability and dependency among elderly humans worldwide. AD is thought to be a disease unique to humans although several other animals develop some aspects of AD-like pathology. Odontocetes (toothed whales) share traits with humans that suggest they may be susceptible to AD. The brains of 22 stranded odontocetes of five different species were examined using immunohistochemistry to investigate the presence or absence of neuropathological hallmarks of AD: amyloid-beta plaques, phospho-tau accumulation and gliosis. Immunohistochemistry revealed that all aged animals accumulated amyloid plaque pathology. In three animals of three different species of odontocete, there was co-occurrence of amyloid-beta plaques, intraneuronal accumulation of hyperphosphorylated tau, neuropil threads and neuritic plaques. One animal showed well-developed neuropil threads, phospho-tau accumulation and neuritic plaques, but no amyloid plaques. Microglia and astrocytes were present as expected in all brain samples examined, but we observed differences in cell morphology and numbers between individual animals. The simultaneous occurrence of amyloid-beta plaques and hyperphosphorylated tau pathology in the brains of odontocetes shows that these three species develop AD-like neuropathology spontaneously. The significance of this pathology with respect to the health and, ultimately, death of the animals remains to be determined. However, it may contribute to the cause(s) of unexplained live-stranding in some odontocete species and supports the 'sick-leader' theory whereby healthy conspecifics in a pod mass strand due to high social cohesion.

Commerson’s dolphin population structure: evidence for female phylopatry and male dispersal

A key in species conservation is understanding the amount and distribution of genetic diversity and how environmental changes that occurred in the recent past may have influenced current patterns of population structure. Commerson’s dolphin, Cephalorhynchus commersonii, has two subspecies, one of which is endemic to South America (C. commersonii commersonii) and little is known about its population genetics. Our objective was to investigate the population genetics of this subspecies throughout its distribution. Using 70 skin samples and information available in GenBank, 308 mitochondrial DNA sequences and 28 species-specific microsatellites were analyzed. The species presented low genetic diversity when compared to other dolphin species, but was consistent with other species within the genus. Strong population structure based on mitochondrial DNA was exhibited throughout its entire distribution, a pattern consistent with female philopatry. However, this pattern was not detected when using microsatellites, suggesting male-mediated gene flow. Demographic tests suggested a population expansion beginning approximately 15,000 years ago, after the Last Glacial Maximum. In a climate change scenario, we recommended considering each sampling location as an independent population management unit in order to evaluate the impact of possible environmental changes on the distribution of genetic information within the species.

Acoustic identification and classification of four dolphin species in the Brazilian marine area affected by the largest tailings dam failure disaster.

Passive acoustic monitoring (PAM) is an increasingly used technique to access the occurrence, distribution, and abundance of cetaceans that may be visually unavailable most of the time. The largest tailings dam failure disaster occurred on 5 November 2015, when the Fundão dam collapsed, releasing over 50 million cubic meters of tailings into the Doce River basin; 14 days later, the tailings plume reached the Atlantic Ocean. PAM was implemented in the concerned area and cetacean species were acoustically identified. Whistles and clicks of visual and acoustic matches were used to predict and classify exclusive acoustic records through random forest models. The identified species were Guiana, rough-toothed, and bottlenose dolphins. Additionally, the franciscana, the most threatened cetacean in the western South Atlantic Ocean, was also acoustically identified. The whistle classifier had 86.9% accuracy with final frequency, duration, and maximum frequency ranked as the most important parameters. The clicks classifier had 86.7% accuracy with peak frequency and 3 dB bandwidth as the most important parameters for classifying species. Considering the potential effect of the increase in turbidity on sound transmission, such as attenuation, the presented classifier should be continuously improved with novel data collected from long-term acoustic monitoring.

Seasonal variation and group size affect movement patterns of two pelagic dolphin species (Lagenorhynchus obscurus and Delphinus delphis).

Movement is a key factor in the survival and reproduction of most organisms with important links to bioenergetics and population dynamics. Animals use movement strategies that minimize the costs of locating resources, maximizing energy gains. Effectiveness of these strategies depends on the spatial distribution, variability and predictability of resources. The study of fine-scale movement of small cetaceans in the pelagic domain is limited, in part because of the logistical difficulties associated with tagging and tracking them. Here we describe and model the fine-scale movement patterns of two pelagic dolphin species using georeferenced movement and behavioral data obtained by tracking dolphin groups on board small vessels. Movement patterns differed by species, group sizes and seasons. Dusky dolphin groups moved shorter distances when feeding and longer distances when traveling whereas the common dolphin did the same only when they moved in large groups. In summer, both dolphins cover longer distances in a more linear path, while in winter the movement is more erratic and moving shorter distances. Both species of dolphins prey on small pelagic fishes, which are patchily distributed and show seasonal variability in school sizes and distribution. However, dusky dolphins rely on anchovy to a larger extent than common dolphins. In Nuevo Gulf, anchovy shoals are smaller and separated by shorter distances in winter and dusky dolphins´ movement pattern is consistent with this. Dusky and common dolphins are impacted by tourism and fisheries. Further modelling of movement could be inform spatial based management tools.

Spatial, temporal and demographic patterns of cetacean strandings in the northcentral Gulf of Mexico

There are few published reports that summarise long‐term stranding data for cetaceans in the Gulf of Mexico (GoM). Cetacean stranding data from Alabama (AL) in the northcentral GoM have been recorded since 1978, with dedicated stranding response beginning in 1987, providing an opportunity to characterise spatial, temporal and demographic stranding patterns for this unique area, which links the eastern and western northern GoM coastline. To elucidate long‐term patterns, we analysed stranding records in AL from 1978–2018, taking into consideration the effects of periodic unusual mortality events (UMEs) on stranding demographics. During this 41‐year period, 774 stranding events were recorded involving at least 13 different cetacean species. Common bottlenose dolphins (Tursiops truncatus) were the most reported stranded cetacean (n = 692, 89.4%), followed by Stenella spp. (n = 31, 4.0%). Spatial analysis revealed three stranding hotspots for bottlenose dolphins and an additional hotspot for non‐bottlenose dolphin species that may represent a geographic influence in the northcentral GoM for strandings of offshore cetaceans. Because strandings were dominated by bottlenose dolphins, additional demographic analyses were possible for this species. Strandings occurred most often in the spring (March–May), and females and foetuses stranded more often in calving (January–April) than non‐calving season, consistent with increased mortality related to birthing or reproductive‐associated events. Subadults were found stranded more often than other size classes, indicating a potential stranding bias for this age class. These data are critical to guide future stranding response efforts, define vulnerable populations and help understand causes of mortality through time in the northcentral GoM. Our findings also highlight the importance of long‐term, consistent stranding response to enable identifying spatial and temporal trends that are necessary to support meaningful, range‐wide management and conservation.

The effects of human care on the blowhole and gut microbiotas of two cohabiting dolphin species based on a year-round surveillance

Understanding the effects of human care on the dynamics of the host-associated microbiota is critical for the health management of dolphins living in an aquarium. Yet this aspect remains relatively unexplored. Here, by utilizing 16S rRNA gene sequencing, we profiled the blowhole and gut bacterial communities of two bottlenose dolphins (Tursiops truncatus) and a Chinese white dolphin (Sousa chinensis) reared in the same indoor pool, based on year-round surveillance. In addition, we compared these dolphin microbiotas with those previously published datasets from wild dolphins. Our results showed that both the blowhole and the gut of the two dolphin species under human care shared a more similar microbiome than members of the same dolphin species across different habitats (human care vs wild). However, the effects of human care on the dolphin microbiome from the two body sites varied. In the aquarium, bacterial alpha diversities differed significantly between the two body sites, and the seasonal stability of the bacterial community was more evident in the gut than in the blowhole. Additionally, the blowhole bacterial composition and the predicted functional capacity from the two dolphin species showed differences and were less convergent than their gut microbiota over a decade-long cohabitation. Further analyses showed that heterogeneous and homogeneous selections (i.e., deterministic processes) contributed more to the blowhole than to the gut bacterial communities, while a dispersal limitation (i.e., a stochastic process) was more important for the gut microbiota. The present study provides the first comparative evidence that the gut microbiota may be more plastic in response to the human care environment than the blowhole microbiota. This improves our understanding of dolphin health management under human care and helps to predict their microbial responses to environmental changes.

Dolphins and sea turtles may host zoonotic parasites and pathogenic bacteria as indicators of anthropic pressure in the Gulf of Taranto (Northern Ionian Sea, Central-Eastern Mediterranean Sea)

The occurrence of protozoan parasites Giardia duodenalis and Cryptosporidium spp. such as the pathogenic bacteria Salmonella spp. and Escherichia coli was molecularly investigated in the following free ranging species of striped dolphins (Stenella coeruleoalba), Risso’s dolphins (Grampus griseus) as well as loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtles living in the Gulf of Taranto (Mediterranean Sea). Out of forty-one investigated individuals belonging to the 4 species, 13 (31.7%) were positive to one or more pathogens and zoonotic G. duodenalis assemblage A, Cryptosporidium parvum and S. enterica were identified in striped dolphins, loggerhead and green sea turtles. In this work, the presence of these opportunistic pathogens has been investigated in fecal samples of free ranging dolphin and sea turtle species for the first time. Moreover, this is the first record of C. parvum in loggerhead sea turtles. These results may provide baseline data for the potential role of cetaceans and sea turtles as potential sentinel species for zoonotic and terrestrial pathogens in the marine environment.

External indicators of fisheries interactions in known bycaught dolphins from bather protection nets along the KwaZuluNatal coastline, South Africa

Detailed examinations of dolphins incidentally caught in bather protection nets along the KwaZulu‐Natal coastline, South Africa, over the past 10 years have yielded a dataset that can assist in the examination of external signs of bycatch. Investigating these external signs of fisheries interactions could aid in determining whether they could be used as unequivocal indicators of entanglement in stranded dolphins for which cause of death is unknown. The aim of this study was to investigate the occurrence of netmarks and other external injuries on individuals of two dolphin species (Tursiops aduncus and Sousa plumbea), both bycaught and stranded, along the south‐east coast of South Africa. Necropsy reports and photographs of 107 bycaught and 15 stranded dolphins between 2010 and 2017 were investigated to determine prevalence of netmarks and other external injuries in relation to species, sex, age class, and water temperature. Our results indicated that 36% of the bycaught dolphins and 13% of stranded dolphins showed netmarks on the skin. In bycaught animals, females were more likely to show netmarks (58%) and the majority of dolphins with netmarks were immatures (66%; immatures included calves, neonates and subadults). There was little evidence for water temperature affecting the appearance of netmarks. Furthermore, species, sex or age class did not play a significant role in the probability of netmark occurrence. Other external injuries were also observed in the bycaught (3–50%) and stranded animals (7–100%), with subcutaneous bruising being the most prominent sign in bycaught animals. Our study showed that only a small percentage of known bycaught animals actually present external signs of entanglement. Thus, additional evidence, such as histopathological examinations, is required to reliably identify entanglement cases in stranded animals.

Probable signature whistle production in Atlantic white‐sided (Lagenorhynchus acutus) and short‐beaked common (Delphinus delphis) dolphins near Cape Cod, Massachusetts

Probable signature whistle production in Atlantic white‐sided (<i>Lagenorhynchus acutus</i>) and short‐beaked common (<i>Delphinus delphis</i>) dolphins near Cape Cod, Massachusetts

Histomorphological stratification of blubber of three dolphin species from subtropical waters.

Blubber is a highly specialized and dynamic tissue unique to marine mammals and presents a reflection of the individuals' nutrition, environment, and life history traits. Few studies have investigated the histomorphology of cetacean blubber in subtropical environments. The aim of this study was to investigate the blubber histomorphology of three different dolphin species off the subtropical KwaZulu-Natal coast, South Africa, using adipocyte cell size, number, and density. Blubber tissue samples from the saddle area of 43 incidentally bycaught animals (fourSousa plumbea, 36 Tursiops aduncus, and threeDelphinus delphis) were used to compare cell parameters between blubber layers. Samples were divided into the upper third (corresponding to the superficial layer closest to the epidermis), middle third, and lower third (corresponding to the deep layer). For T. aduncus, factors potentially affecting blubber histomorphology, such as sex, age class, and season, were also assessed. Our results showed that no stratification was present in S. plumbea, which could be ascribed to the species' warmer inshore habitat, large body size, and apparent lower mobility. For T. aduncus and D. capensis, however, blubber stratification was determined, characterized by a gradual transition of cell size, number, and density between layers rather than clearly defined layers. Significant differences in adipocyte cell number and density were found for different sexes and age classes of T. aduncus. However, there were no significant differences between seasons, which was attributed to the small temperature differences between seasons. This study represents the first investigation of odontocete blubber histomorphology in subtropical waters. It is recommended that future studies investigate blubber lipid content, while also taking into consideration the reproductive status of the females and the temperature range of their study area. It is hoped that our results, in conjunction with histopathology and other health indicators, could assist in assessing health and body condition.

Detection of Cetacean Poxvirus in Peruvian Common Bottlenose Dolphins (Tursiops truncatus) Using a Pan-Poxvirus PCR.

Cetacean poxviruses (CePVs) cause ‘tattoo’ skin lesions in small and large cetaceans worldwide. Although the disease has been known for decades, genomic data for these poxviruses are very limited, with the exception of CePV-Tursiops aduncus, which was completely sequenced in 2020. Using a newly developed pan-pox real-time PCR system targeting a conserved nucleotide sequence located within the Monkeypox virus D6R gene, we rapidly detected the CePV genome in typical skin lesions collected from two Peruvian common bottlenose dolphins (Tursiops truncatus) by-caught off Peru in 1993. Phylogenetic analyses based on the sequencing of the DNA polymerase and DNA topoisomerase genes showed that the two viruses are very closely related to each other, although the dolphins they infected pertained to different ecotypes. The poxviruses described in this study belong to CePV-1, a heterogeneous clade that infects many species of dolphins (Delphinidae) and porpoises (Phocoenidae). Among this clade, the T. truncatus CePVs from Peru were more related to the viruses infecting Delphinidae than to those detected in Phocoenidae. This is the first time that CePVs were identified in free-ranging odontocetes from the Eastern Pacific, surprisingly in 30-year-old samples. These data further suggest a close and long-standing pathogen–host co-evolution, resulting in different lineages of CePVs.

Reduction of Species Identification Errors in Surveys of Marine Wildlife Abundance Utilising Unoccupied Aerial Vehicles (UAVs)

The advent of unoccupied aerial vehicles (UAVs) has enhanced our capacity to survey wildlife abundance, yet new protocols are still required for collecting, processing, and analysing image-type observations. This paper presents a methodological approach to produce informative priors on species misidentification probabilities based on independent experiments. We performed focal follows of known dolphin species and distributed our imagery amongst 13 trained observers. Then, we investigated the effects of reviewer-related variables and image attributes on the accuracy of species identification and level of certainty in observations. In addition, we assessed the number of reviewers required to produce reliable identification using an agreement-based framework compared with the majority rule approach. Among-reviewer variation was an important predictor of identification accuracy, regardless of previous experience. Image resolution and sea state exhibited the most pronounced effects on the proportion of correct identifications and the reviewers’ mean level of confidence. Agreement-based identification resulted in substantial data losses but retained a broader range of image resolutions and sea states than the majority rule approach and produced considerably higher accuracy. Our findings suggest a strong dependency on reviewer-related variables and image attributes, which, unless considered, may compromise identification accuracy and produce unreliable estimators of abundance.

First record of sharksucker Echeneis naucrates (Perciformes, Echeneidae) associated with a young Guiana dolphin Sotalia guianensis (Cetartiodactyla, Delphinidae) in north-eastern Brazil

AbstractSuckerfish attached to dolphin species have been extensively reported worldwide, yet such association has been rarely seen in the tropical and shallow waters of South America. In Brazil, the Guiana dolphin Sotalia guianensis is distributed along almost the entire extent of the coast and only one case of association with suckerfish has been published. Here we report on a sharksucker Echeneis naucrates associated with a young Guiana dolphin on the north-eastern coast of Brazil. The juvenile dolphin with an attached sharksucker was observed on two occasions separated by a 47-day period; we hypothesize the occurrence of host attachment fidelity. The present report adds information to better discuss the ecological interactions between echeneids and dolphins, and expands the baseline information on cetacean species serving as host to suckerfish.

Follicular and Hormonal Changes after Estrous Synchronization in Bottlenose Dolphins.

To gain more knowledge about the influence of hormone regulation on follicle development, ovarian ultrasounds were performed, and urinary hormone profiles were determined in ovulating and non-ovulating female bottlenose dolphins (n = 15) following estrus synchronization with altrenogest. Ovarian ultrasounds were conducted daily, post-synchronization to describe follicular recruitment in relation to the endocrine profile. Follicle sizes were grouped into very small (VSM), small (SM), medium (MD) and large (LG). In ovulating females, two follicular waves were identified, and follicular deviation toward establishing a dominant follicle only occurred during the second wave. For non-ovulating females, only the first wave was observed. For all urinary hormones, the non-ovulating group presented significantly lower concentrations of follicle-stimulating hormone (uFSH), luteinizing hormone (uLH), estrone conjugates (uE1-C) and estriol (uE3) but similar progestagen and cortisol concentrations compared to the ovulating group. Concentrations of uE1-C and uE3 and the numbers of MD and LG follicles significantly (P < 0.05) increased, while uFSH concentrations significantly (P < 0.05) decreased as ovulation approached. Urinary LH significantly increased concurrently with increasing numbers of LG follicles and decreasing numbers of SM follicles. The characterization of follicular development and its relationship with hormone assessment complements our understanding of follicular recruitment post-synchronization in bottlenose dolphins and provides new information concerning differences between ovulating and non-ovulating females in response to an estrous synchronization protocol.Lay summaryMany species of fresh and saltwater dolphins and porpoises are facing increasing pressure for food and habitats due to human activities. One of the primary aspects that can be affected by such activities is reproduction. The bottlenose dolphin has been successfully bred in zoos and aquariums for at least 70 years, and they can be trained for several voluntary behaviors that enable medical examinations. Therefore, they represent a unique resource for research and understanding of normal dolphin reproduction. In this research, voluntary ultrasound exams and urine samples from 15 female dolphins were used to describe changes in their ovaries. The resulting descriptions and comparisons provide insight into the unique ovarian physiology of bottlenose dolphins and into the differences between animals after treatment. This information adds to the body of knowledge which one day may be used for developing advanced reproductive techniques to help preserve endangered species of dolphins.

Extracting foraging behavior from passive acoustic monitoring data to better understand harbor porpoise (Phocoena phocoena) foraging habitat use

AbstractFor odontocetes, passive acoustic monitoring (PAM) can be used to differentiate between occurrence and foraging through analysis of click characteristics. Feeding buzzes and navigation/searching echolocation clicks of harbor porpoise (Phocoena phocoena) were differentiated within C‐POD data from northwest Ireland between 2009 and 2017. The spatiotemporal distribution of foraging behavior was investigated using generalized additive modelling, at multiple temporal scales. Both the presence/absence of buzzes and foraging intensity (defined by buzz:click ratios) were determined. Feeding buzzes were identified in one third of porpoise positive hours, ranging from 15% in summer, to 40% in autumn, highlighting seasonal variation irrespective of porpoise occurrence. Complex interannual variation in foraging behavior was also shown across the time series. A strong nocturnal peak in foraging intensity was observed. We found increased porpoise foraging with dolphin species detections within the same hour, and a negative impact of construction activities, involving both impulsive and broadband noise. Results highlight the value of long‐term acoustic time series, by quantifying variation, and show that extracting foraging behavior from occurrence data can help to unravel habitat use patterns, responses to disturbance, and seasonal changes in behavior. Understanding when and how a species uses an area can better inform marine spatial planning and help mitigate anthropogenic impacts.

The ecology and evolution of human‐wildlife cooperation

AbstractHuman‐wildlife cooperation is a type of mutualism in which a human and a wild, free‐living animal actively coordinate their behaviour to achieve a common beneficial outcome.While other cooperative human‐animal interactions involving captive coercion or artificial selection (including domestication) have received extensive attention, we lack integrated insights into the ecology and evolution of human‐wildlife cooperative interactions.Here, we review and synthesise the function, mechanism, development, and evolution of human‐wildlife cooperation.Active cases involve people cooperating with greater honeyguide birds and with two dolphin species, while historical cases involve wolves and orcas.In all cases, a food source located by the animal is made available to both species by a tool‐using human, coordinated with cues or signals.The mechanisms mediating the animal behaviours involved are unclear, but they may resemble those underlying intraspecific cooperation and reduced neophobia.The skills required appear to develop at least partially by social learning in both humans and the animal partners. As a result, distinct behavioural variants have emerged in each type of human‐wildlife cooperative interaction in both species, and human‐wildlife cooperation is embedded within local human cultures.We propose multiple potential origins for these unique cooperative interactions, and highlight how shifts to other interaction types threaten their persistence.Finally, we identify key questions for future research. We advocate an approach that integrates ecological, evolutionary and anthropological perspectives to advance our understanding of human‐wildlife cooperation. In doing so, we will gain new insights into the diversity of our ancestral, current and future interactions with the natural world.Read the freePlain Language Summaryfor this article on the Journal blog.

Who Is in Handicrafts: Tooth Morphology and Age Determination as Tools to Assess Vulnerable Dolphins Sotalia spp. Supplying the Trade of Artisanal Charms in Brazil

In Brazil, dolphins’ body parts are commonly used as traditional amulets, named as love-charms, while dolphins’ teeth are commercialized in handcrafted necklaces and bracelets. Recent studies on forensic genetics confirmed the Guiana dolphin,Sotalia guianensis, as the principal target of the love-charms trading, with specimens incidentally captured in gillnets suggested as the primary source. As additional support for these investigations, we characterized tooth morphotypes and ages of dolphins used in the construction of traditional crafts, with the main objective of detecting the dolphin species and population groups most affected by this trade. Teeth collected from necklaces, bracelets, and earrings, sold in public markets from three major cities of Northern and Northeastern Brazil (Belém = 99, São Luís = 4, and Fortaleza =15), were analyzed using four morphological measurements: tooth total length (TL), root diameter (RD), crown length (CL), and cingulum diameter (CID). An unweighted pair group method using arithmetic means (UPGMA), with Euclidean distances as a measure of dissimilarity, multivariate analysis of variance (MANOVA), and principal component analysis (PCA) were used to detect tooth morphotypes in the samples. Ages were obtained by counting the growth layer groups (GLGs) deposited in dentine. Two different groups of teeth were detected presumably belonging to the speciesSotalia guianensisandS. fluviatilis. Handicrafts showed a diverse age composition, ranging from 2 to 30 years, with a multimodal distribution (Mean =11 ± 7 SD, Median = 10, Mode = 4, 8, 19), similar to dolphin populations affected by fishery interaction. Results suggested that juveniles individuals and adults younger than 20 years, from bothSotaliaspecies, probably incidentally captured, are the principal source of handicrafts, and raise concern about the greater vulnerability of young age categories presented in this trade.

Pingers are effective in reducing net entanglement of river dolphins

Ganges River dolphins echolocate, but this mechanism is inadequate for poor sonar-echoing objects such as the monofilament gillnets, causing considerable net entanglement related mortalities. Net entanglement related deaths are one of the major causes of cetacean population decline around the world. Experiments were carried out to understand the use of pingers—an acoustic deterrent, in aiding the deterrence of dolphins from fishing nets. Based on the dolphin clicks recorded, in an experimental setup spanning 36 days, a 90% deterrence was found; 22.87 ± 0.71 SE dolphin detection positive minutes per hour near non-pingered nets versus 2.20 ± 0.33 SE per hour near pingered net. Within 30 m radii of nets, visual encounters of non-calf reduced by 52% and calf by 9%, in the presence of pingers. No evidence of habituation to pingers, habitat avoidance in dolphins after pinger removal or a change in fish catch in nets because of pingers was found during the study. While the effectiveness of pingers on calves and fish catch needs further experimentation, the use of pingers to minimize net entanglement mortalities in the Ganges River dolphins seems to be the most promising solution currently available. These results have critical implications for the conservation of other species of river dolphins around the world.