Summary Humpback dolphins (genus Sousa ) are medium-sized delphinids found in shallow ( Sousa teu... more Summary Humpback dolphins (genus Sousa ) are medium-sized delphinids found in shallow ( Sousa teuszii ), (2) Indian Ocean humpback ( S. plumbea ), (3) Indo-Pacific humpback ( S. chinensis ), and (4) Australian humpback ( S. sahulensis ) dolphins. Information on the ecology, behavior and life history of all humpback dolphins remains scarce. Most study populations to date indicate that all species occur in small numbers, with most populations confirmed or suspected to be declining and threatened. Major threats affecting all species include habitat degradation and loss, and entanglement in fishing gear. Research efforts and conservation actions tailored to each species are needed to assess anthropogenic impacts, and develop strategies to eliminate or mitigate threats.
Group living is a critical component of the ecology of social animals such as delphinids. In many... more Group living is a critical component of the ecology of social animals such as delphinids. In many studies on these animals, groups represent sampling units that form the basis of the collection and analysis of data on their abundance, behavior, and social structure. Nevertheless, defining what constitutes a group has proven problematic. There is inconsistency in the terms and criteria used and many definitions lack biological justification. We conducted a literature review and an online expert survey to assess various terms (group, school, party, and pod), and their definitions as applied to delphinids to identify issues to ultimately make recommendations. Of 707 studies analyzed, 325 explicitly defined one or more terms, providing 344 definitions. Additionally, 192 definitions were obtained from the survey. Among these definitions, group was the most common term used (review: 286 definitions, 83.1%; survey: 69 definitions, 35.9%) and the most familiar to the survey respondents (73 respondents, 100.0%). In definitions of group, spatial proximity was the most used criterion (review: 200 definitions, 71.2%; survey: 53 definitions, 81.5%) followed by behavior (review: 176 definitions, 62.6%; survey: 38 definitions, 58.5%). The terms and criteria used to define delphinid groups vary considerably. Rather than proposing a single formal definition, we instead recommend that the term group and spatial proximity criteria be used to define sampling units of individuals observed in the field. Furthermore, we propose a process for formulating definitions that involves analyzing interindividual distances to determine naturally occurring patterns that are indicative of group membership. Although this process is based principally on the spatial proximity of individuals, it could also incorporate the behavior of group members by evaluating the influence of behavior on interindividual distances. Such a process produces definitions that are biologically meaningful and compatible across studies and populations, thus increasing our ability to draw strong conclusions about group living in delphinids.
The Indo-Pacific humpback dolphin (Sousa chinensis – ‘Sousa’ hereafter) has been identified as a ... more The Indo-Pacific humpback dolphin (Sousa chinensis – ‘Sousa’ hereafter) has been identified as a “priority concern” for conservation management in Australia. Currently, no peer-reviewed scientific literature exists on Sousa in Western Australian waters, where they are listed as a “data deficient” species. This lack of available information hinders rigorous impact assessments, as well as conservation and management efforts for this coastal species. As part of broader studies estimating genetic connectivity for three coastal delphinids (Indo-Pacific bottlenose dolphins, Tursiops aduncus; Australian snubfin dolphins, Orcaella heinshoni; and Sousa) across northwestern Australia, photo-identification images of Sousa groups were obtained off the North West Cape from Ningaloo Reef to Exmouth, WA (21o56’S, 114o07’E). Preliminary results of the non-dedicated photo-identification efforts identified fifty-three adult and juvenile Sousa and six calves during 18 days of, or part there-of, survey effort in April 2010 over ca. ~80 km coastline of the near-shore waters around the Cape. A continued increase in the cumulative discovery curve of photoidentified individuals throughout the short study period indicates that only a subsection of Sousa in the area was identified. The North West Cape, Exmouth, represents the southwestern limit of the species’ Australian distribution and may be an important stronghold for Sousa in Western Australia. These initial findings indicate further research into this population of Sousa is urgent given the recent opening of the Exmouth Gulf to petroleum exploration, coupled with increasing port and tourism activities in the area.
Abstract Numerous species of marine megafauna are at risk of extinction and understanding their g... more Abstract Numerous species of marine megafauna are at risk of extinction and understanding their genetic population structure and demographic history is essential for their conservation. We used mitochondrial DNA and 18 nuclear microsatellite loci, on the largest genetic dataset compiled to date on Australian humpback dolphins (eight sampling sites, 159 samples), to assess their genetic diversity, gene flow and past demographic history along the east coast of Queensland, Australia. Levels of genetic diversity were low (mtDNA: h = 0–0.52, π = 0–0.007; nDNA: Ho = 0.27–0.41; AR = 1.7–2.4). Both mitochondrial (ΦST = 0.49, P = 0.001) and nuclear markers (FST = 0.14, P = 0.001) showed strong genetic structure among sampling sites. Four putative populations were identified, with little contemporary gene flow (m = 0.017 to 0.047) among populations. Genetic divergence follows an isolation-by-distance model (r = 0.38, P = 0.0001), with an apparent restriction in gene flow occurring at scales of 382–509 km. Estimates of contemporary effective population size were low (Ne = 11.5–31.2), with signatures of genetic bottlenecks for all putative populations about 50–150 generations ago. The current low levels of genetic diversity, gene flow, and effective population size in Australian humpback dolphins indicate the effects of historical population bottlenecks and/or founder events during the late Holocene period (~1250–3750 years ago); probably associated with sea level fall and increased intensity of El Nino Southern Oscillation-climatic events. Our results raise important conservation concerns and emphasize the vulnerability of Australian humpback dolphins to stochastic demographic, genetic and environmental processes. Conservation strategies should focus on promoting connectivity among local populations and reducing direct causes of human-related mortality.
Ecological niche theory predicts the coexistence of closely related species is promoted by resour... more Ecological niche theory predicts the coexistence of closely related species is promoted by resource partitioning in space and time. Australian snubfin (Orcaella heinsohni) and humpback (Sousa sahulensis) dolphins live in sympatry throughout most of their range in northern Australian waters. We compared stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in their skin to investigate resource partitioning between these ecologically similar species. Skin samples were collected from live Australian snubfin (n = 31) and humpback dolphins (n = 23) along the east coast of Queensland in 2014–2015. Both species had similar δ13C and δ15N values and high (>50%) isotopic niche space overlap, suggesting that they feed at similar trophic levels, have substantial dietary overlap, and rely on similar basal food resources. Despite similarities, snubfin dolphins were more likely to have a larger δ15N value than humpback dolphins, indicating they may forage on a wider diversity of prey. Humpback dolphins were more likely to have a larger δ13C range suggesting they may forage on a wider range of habitats. Overall, results suggest that subtle differences in habitat use and prey selection are likely the principal resource partitioning mechanisms enabling the coexistence of Australian snubfin and humpback dolphins.
Summary Humpback dolphins (genus Sousa ) are medium-sized delphinids found in shallow ( Sousa teu... more Summary Humpback dolphins (genus Sousa ) are medium-sized delphinids found in shallow ( Sousa teuszii ), (2) Indian Ocean humpback ( S. plumbea ), (3) Indo-Pacific humpback ( S. chinensis ), and (4) Australian humpback ( S. sahulensis ) dolphins. Information on the ecology, behavior and life history of all humpback dolphins remains scarce. Most study populations to date indicate that all species occur in small numbers, with most populations confirmed or suspected to be declining and threatened. Major threats affecting all species include habitat degradation and loss, and entanglement in fishing gear. Research efforts and conservation actions tailored to each species are needed to assess anthropogenic impacts, and develop strategies to eliminate or mitigate threats.
Group living is a critical component of the ecology of social animals such as delphinids. In many... more Group living is a critical component of the ecology of social animals such as delphinids. In many studies on these animals, groups represent sampling units that form the basis of the collection and analysis of data on their abundance, behavior, and social structure. Nevertheless, defining what constitutes a group has proven problematic. There is inconsistency in the terms and criteria used and many definitions lack biological justification. We conducted a literature review and an online expert survey to assess various terms (group, school, party, and pod), and their definitions as applied to delphinids to identify issues to ultimately make recommendations. Of 707 studies analyzed, 325 explicitly defined one or more terms, providing 344 definitions. Additionally, 192 definitions were obtained from the survey. Among these definitions, group was the most common term used (review: 286 definitions, 83.1%; survey: 69 definitions, 35.9%) and the most familiar to the survey respondents (73 respondents, 100.0%). In definitions of group, spatial proximity was the most used criterion (review: 200 definitions, 71.2%; survey: 53 definitions, 81.5%) followed by behavior (review: 176 definitions, 62.6%; survey: 38 definitions, 58.5%). The terms and criteria used to define delphinid groups vary considerably. Rather than proposing a single formal definition, we instead recommend that the term group and spatial proximity criteria be used to define sampling units of individuals observed in the field. Furthermore, we propose a process for formulating definitions that involves analyzing interindividual distances to determine naturally occurring patterns that are indicative of group membership. Although this process is based principally on the spatial proximity of individuals, it could also incorporate the behavior of group members by evaluating the influence of behavior on interindividual distances. Such a process produces definitions that are biologically meaningful and compatible across studies and populations, thus increasing our ability to draw strong conclusions about group living in delphinids.
The Indo-Pacific humpback dolphin (Sousa chinensis – ‘Sousa’ hereafter) has been identified as a ... more The Indo-Pacific humpback dolphin (Sousa chinensis – ‘Sousa’ hereafter) has been identified as a “priority concern” for conservation management in Australia. Currently, no peer-reviewed scientific literature exists on Sousa in Western Australian waters, where they are listed as a “data deficient” species. This lack of available information hinders rigorous impact assessments, as well as conservation and management efforts for this coastal species. As part of broader studies estimating genetic connectivity for three coastal delphinids (Indo-Pacific bottlenose dolphins, Tursiops aduncus; Australian snubfin dolphins, Orcaella heinshoni; and Sousa) across northwestern Australia, photo-identification images of Sousa groups were obtained off the North West Cape from Ningaloo Reef to Exmouth, WA (21o56’S, 114o07’E). Preliminary results of the non-dedicated photo-identification efforts identified fifty-three adult and juvenile Sousa and six calves during 18 days of, or part there-of, survey effort in April 2010 over ca. ~80 km coastline of the near-shore waters around the Cape. A continued increase in the cumulative discovery curve of photoidentified individuals throughout the short study period indicates that only a subsection of Sousa in the area was identified. The North West Cape, Exmouth, represents the southwestern limit of the species’ Australian distribution and may be an important stronghold for Sousa in Western Australia. These initial findings indicate further research into this population of Sousa is urgent given the recent opening of the Exmouth Gulf to petroleum exploration, coupled with increasing port and tourism activities in the area.
Abstract Numerous species of marine megafauna are at risk of extinction and understanding their g... more Abstract Numerous species of marine megafauna are at risk of extinction and understanding their genetic population structure and demographic history is essential for their conservation. We used mitochondrial DNA and 18 nuclear microsatellite loci, on the largest genetic dataset compiled to date on Australian humpback dolphins (eight sampling sites, 159 samples), to assess their genetic diversity, gene flow and past demographic history along the east coast of Queensland, Australia. Levels of genetic diversity were low (mtDNA: h = 0–0.52, π = 0–0.007; nDNA: Ho = 0.27–0.41; AR = 1.7–2.4). Both mitochondrial (ΦST = 0.49, P = 0.001) and nuclear markers (FST = 0.14, P = 0.001) showed strong genetic structure among sampling sites. Four putative populations were identified, with little contemporary gene flow (m = 0.017 to 0.047) among populations. Genetic divergence follows an isolation-by-distance model (r = 0.38, P = 0.0001), with an apparent restriction in gene flow occurring at scales of 382–509 km. Estimates of contemporary effective population size were low (Ne = 11.5–31.2), with signatures of genetic bottlenecks for all putative populations about 50–150 generations ago. The current low levels of genetic diversity, gene flow, and effective population size in Australian humpback dolphins indicate the effects of historical population bottlenecks and/or founder events during the late Holocene period (~1250–3750 years ago); probably associated with sea level fall and increased intensity of El Nino Southern Oscillation-climatic events. Our results raise important conservation concerns and emphasize the vulnerability of Australian humpback dolphins to stochastic demographic, genetic and environmental processes. Conservation strategies should focus on promoting connectivity among local populations and reducing direct causes of human-related mortality.
Ecological niche theory predicts the coexistence of closely related species is promoted by resour... more Ecological niche theory predicts the coexistence of closely related species is promoted by resource partitioning in space and time. Australian snubfin (Orcaella heinsohni) and humpback (Sousa sahulensis) dolphins live in sympatry throughout most of their range in northern Australian waters. We compared stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in their skin to investigate resource partitioning between these ecologically similar species. Skin samples were collected from live Australian snubfin (n = 31) and humpback dolphins (n = 23) along the east coast of Queensland in 2014–2015. Both species had similar δ13C and δ15N values and high (>50%) isotopic niche space overlap, suggesting that they feed at similar trophic levels, have substantial dietary overlap, and rely on similar basal food resources. Despite similarities, snubfin dolphins were more likely to have a larger δ15N value than humpback dolphins, indicating they may forage on a wider diversity of prey. Humpback dolphins were more likely to have a larger δ13C range suggesting they may forage on a wider range of habitats. Overall, results suggest that subtle differences in habitat use and prey selection are likely the principal resource partitioning mechanisms enabling the coexistence of Australian snubfin and humpback dolphins.
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