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—Difference in color pattern of white patch of adult Dall's porpoise: a) Phocoenoides dalli-type, b) P. truei-type.
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The taxonomic status of the 2 morphologically distinct forms of Dall's porpoises, Phocoenoides dalli (dalli- and truei-type) remains unresolved. To address this uncertainty, mitochondrial DNA (mtDNA) sequences were used to estimate phylogenetic relationships between the 2 types and, in conjunction with microsatellite markers, to test genetic differ...
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Citations
... The dalli-115 type is found throughout the range of the species, while the truei-type is found in a 116 smaller area of the northwestern North Pacific. The taxonomic status of the two types 117 remains unclear as their genetic differences are no larger than the differences 118 between neighboring populations of the dalli-type (Escorza- Treviño et al. 2004). ...
Unlike the large number of species of true dolphins, there are only seven porpoise or phocoenid species, inhabiting different habitats and climate zones. They range from ice-covered water in the Arctic to the subantarctic islands through tropic waters and even in freshwater river systems. Some species like the harbour porpoise are widely distributed in both the Atlantic and the Pacific, while the vaquita has the most restricted range of any cetacean and only lives in a small northern part of the Gulf of California, or Sea of Cortez, in northwestern Mexico, where it is now close to extinction due to illegal fishery. Little is known about porpoise species compared to many dolphin species as they generally have an elusive behavior or live away from human attention. However, the finless porpoise and the harbour porpoise have been kept in captivity for many years with success, contributing to knowledge on social interactions, breeding behavior, and sensory physiology. In recent years, a growing number of studies of wild porpoises using advanced electronic tagging devices have greatly improved our knowledge of movements, acoustic behavior, feeding ecology, and reactions to noise disturbance. We now know that harbour porpoises are widely distributed over most of the deep north Atlantic during winter and therefore not only a coastal species as previously thought. We also see very similar echolocation behavior between the finless and the harbour porpoises, showing an almost constant hunt for food, but also inactive periods that may be interpreted as sleeping. Ship noise has been shown to have a significant effect on feeding buzzes, and loud sounds may cause pauses in echolocation and fast movements away from the sound source, which again may result in bycatch and in rare cases mass stranding. Tagging data have also shown that harbour porpoises are much more social than previously thought and have acoustic contact to conspecifics up to 58% of the time between mother and calf and 36% between animals tagged alone. With these new findings, our growing understanding of porpoise behavior has opened a window to their elusive lives that could help improve management and conservation decisions.
... This study aimed to determine interspecific habitat differences. Therefore, sightings of distinct intraspecific populations, such as the dalli and truei types of Dall's porpoise (Kasuya and Jones, 1984;Miyazaki, 1992, 1996;Escorza-Treviño et al., 2004), the northern and southern forms of the short-finned pilot whale (Kasuya et al., 1988;Wada, 1988;Kasuya and Tai, 1993;Miyazaki and Amano, 1994), and coastal and offshore populations of Pacific white-sided dolphin (Lux et al., 1997;Miyazaki and Shikano, 1997a,b;Hayano et al., 2004) were pooled for analyzes. The short-beaked and long-beaked common dolphins are now recognized as distinct species but are similar in appearance and can be confused during onboard sightings (Heyning and Perrin, 1994). ...
Information regarding the distributional patterns of top predators is undoubtedly important for the monitoring and management of marine ecosystems. Nevertheless, previous knowledge on the distributional patterns of cetacean species in relation to physical oceanography is usually limited to a small fraction of each species' range because of their vast distribution and infrequency of encountering many species. We carried out comprehensive analyzes on the distributions of small odontocetes covering almost the entire North Pacific Ocean. Using data from over 300 000 nautical miles (≈ 555 600 km) of dedicated sighting surveys and 7000 school sightings of 14 small odontocete species, which have accumulated for approximately a quarter of a century, we describe interspecific habitat differences in small odontocetes with respect to physical oceanography. Multivariate analyzes were used to discriminate the 14 species into four ecological groups: (i) Subtropical Domain species; (ii) Subarctic Boundary species; (iii) Transitional Domain species; and (iv) Subarctic Domain species. By comparing environmental variables in their habitats with variables indicative of water mass and frontal structures, the four species groups were further divided into several subgroups. Groups at higher latitudes comprised fewer species than those at lower latitudes, while species diversity was maximal at lower and intermediate latitudes. Our findings indicate that large-scale oceanographic structures are important determinants for the present patterns in biogeography and species diversity of small odontocetes.
... This is especially true for cetaceans, for which movements are not limited by physical barriers. Although most cetacean species show wide distributions and high potential for dispersal, their populations usually exhibit some kind of structure [3,4,5,6,7], that may depend on the local distribution of resources and/or their social system [8]. ...
Population differentiation in environments without well-defined geographical barriers represents a challenge for wildlife management. Based on a comprehensive database of individual sighting records (1988-2009) of blue whales from the winter/calving Gulf of California, we assessed the fine-scale genetic and spatial structure of the population using individual-based approaches. Skin samples of 187 individuals were analyzed for nine microsatellite loci. A single population with no divergence among years and months and no isolation by distance (Rxy = 0.1-0.001, p>0.05) were found. We ran two Bayesian clustering methods using Structure and Geneland softwares in two different ways: 1) a general analysis including all individuals in which a single cluster was identified with both softwares; 2) a specific analysis of females only in which two main clusters (Loreto Bay and northern areas, and San Jose-La Paz Bay area) were revealed by Geneland program. This study provides information indicating that blue whales wintering in the Gulf of California are part of a single population unit and showed a fine-scale structure among females, possibly associated with their high site fidelity, particularly when attending calves. It is likely that the loss of genetic variation is minimized by male mediated gene flow, which may reduce the genetic drift effect. Opportunities for kin selection may also influence calf survival and, in consequence, have a positive impact on population demography in this small and endangered population.
... Dall's porpoise are also classified as a single species, but debate exists regarding the taxonomy. Some consider them to be a single species that is phenotypically polymorphic (Ogawa, 1938;Benson and Groody, 1942;Houck, 1976;Rice, 1977;Kasuya, 1978;Shimura and Numachi, 1987;Jefferson, 1988;Escorza-Trevino et al., 2004), while others suggest there is sufficient differentiation to warrant possible classification into either subspecies or separate species (Yocom, 1946;Wilke and Kenyon, 1952;Kuroda, 1954;Tomilin, 1957;Nishiwaki, 1972;Rice, 1998;Amano and Hayano, 2007). The confusion exists because of two predominant phenotypes that are often referred to as the truei-and dalli-types, in which the main physical difference lies in the forward extent of the lateral white flank patches (Figure 2.2). ...
... Hayano et al. (2003) analyzed mtDNA control-region sequences (479bp, with flanking tRNA genes) and detected genetic differentiation among the three populations, with pairwise difference being greatest between the Sea-of-Japan dalli-type population and the other dalli-type population and truei-type population, which were insignificantly different from each other. Escorza-Treviño et al. (2004) analyzed 379 base pairs of the mtDNA control region and 6 microsatellites for 23 truei-type and 113 dalli-type. The mtDNA haplotypes clustered in two distinct clades, each containing both color morphs. ...
We reviewed the subspecies listed by Rice (1998) and those described since (a total of 49, in 19 species), assessing them against the criteria recommended by the recent Workshop on Shortcomings of Cetacean Taxonomy in Relation to Needs of Conservation and Management (Reeves et al., 2004). The workshop suggested that the subspecies concept can be construed to cover two types of entities: a) lineages diverging but not quite far along the continuum of divergence (still having significant gene flow with another lineage or lineages) to be judged as species, and b) lineages that may well be species but for which not enough evidence is yet available to justify their designation as such. As a criterion for support of a subspecies, the workshop suggested as a guideline that there be at least one good line of either morphological or appropriate genetic evidence. "Appropriate" was not defined; the recommendation was that that be left up to the taxonomist authors of subspecies and to their professional peers. A further recommendation was that evidence on distribution, behavior and ecology should be considered not as primary but as supporting evidence, as there was not agreement at the workshop that such characters are necessarily stable (in the case of distribution) or inherent (behavior and ecology).
Heart size and blood oxygen (O2) in Dall's porpoises (Phocoenoides dalli), Pacific white‐sided dolphins (Lagenorhynchus obliquidens), and common bottlenose dolphins (Tursiops truncatus) correlate with reported swim speeds and dive behavior. Deep‐dive capacity is often associated with smaller relative lung masses, larger “inexpensive” tissue masses (locomotor muscle + blubber + bone masses), and larger total O2 stores. To gain insight into dive behaviors and surface travel of small pelagic cetaceans, we compared body compositions of Dall's porpoises, Pacific white‐sided dolphins, and northern right whale dolphins (Lissodelphis borealis) to the bottlenose dolphin. Relative lung masses, inexpensive tissue masses, and total O2 stores of Dall's porpoises and Pacific white‐sided dolphins were consistent with deeper dive capacities than in the coastal bottlenose dolphin. In contrast to known low myoglobin concentrations in northern right whale dolphins, inexpensive tissue mass suggested intermediate dive capacity. The estimated body O2 store of Dall's porpoise was among the highest of any cetacean. The relatively large hearts of Dall's porpoises, Pacific white‐sided dolphins, and northern right whale dolphins are hypothesized as especially important during high‐speed surface travel. Based on similarities in locomotory performance, morphology, and physiology to those of the horse, we consider Dall's porpoise a thoroughbred of the sea.
Dall's porpoise has a stocky body, and it has a short, wide-based, triangular dorsal fin. The dorsal fin is slightly falcate at the tip, but the entire fin may be canted forward in adult males. The tailstock is deepened, especially in adult males, and males have a prominent post-anal hump of connective tissue. There is an extremely short, poorly defined beak. The color pattern is diagnostic. “Dall's” are largely dark gray to black with a large, ventrally continuous white patch that extends up about halfway on each flank. There are two major color morphs, one with a flank patch that extends forward to about the level of the dorsal fin (dalli type) and the other with a flank patch extending to about the level of the flippers (truei type). Dall's porpoises reach maximum known lengths and weights of about 239 cm and 200 kg. Males grow longer and heavier than females, and adult males have secondary sexual characteristics (as discussed earlier). There is a great deal of geographical variation; size, shape, and coloration differences have been documented among different areas of the species' range.
Scientists conducting research on cetaceans have a variety of publication outlets. However, a formal assessment of those options has not been conducted. To better understand the trends in publications regarding dolphins and whales, we surveyed peer-reviewed articles from 9 different databases. Our survey produced 1,628 unique articles involving 16 cetaceans found both in the wild and in captivity. Each article was coded a variety of information: habitat, geographic location, genus, topic, research design, and journal type. The analyses indicated that 68% studies were conducted with wild populations and 29% were performed with captive populations. A quarter of the journals publishing research on dolphins or whales published almost 80% of all the articles selected for this study. Studies were conducted across many different geographic locations and topics. Other major findings elucidated relationships between various variables. As expected, specific topics were more likely associated with certain research designs, habitats, and journal types. One of the most important findings of this study is the limited publication of research conducted with captive cetaceans. While it is important to continue to examine animals in their natural environments, there is much to be learned from studies conducted with animals in captivity. As a group, we must become cognizant of the publication trends which currently describe our research progress as we integrate our knowledge from captivity and the wild.
There are two major color morphs, truei and dalli types, of the Dall's porpoise and the latter includes two minor morphs. A small number of dalli types are found among truei types off the Pacific coast of Japan, where truei types normally winter. Based on differences in the patch size of dalli-type porpoises taken by the harpoon fishery, we determined that those dalli types contain both minor morphs. Although the total number of both types in the sample was similar, the proportion of the two types varied seasonally. Sex ratio, body length, and maturity rate were different among the dalli and truei types. These facts strongly suggest that these dalli types were not members of the truei-type population and were actually migrants from adjacent dalli-type populations. The definition of the subspecies Phocoenoides dalli dalli and P. d. truei as polymorphic groups is not supported, although we consider that each of the three color morphs is worthy of full subspecific status.
Prior studies of phylogenetic relationships among phocoenids based on morphology and molecular sequence data conflict and yield unresolved relationships among species. This study evaluates a comprehensive set of cranial, postcranial, and soft anatomical characters to infer interrelationships among extant species and several well-known fossil phocoenids, using two different methods to analyze polymorphic data: polymorphic coding and frequency step matrix. Our phylogenetic results confirmed phocoenid monophyly. The division of Phocoenidae into two subfamilies previously proposed was rejected, as well as the alliance of the two extinct genera Salumiphocaena and Piscolithax with Phocoena dioptrica and Phocoenoides dalli. Extinct phocoenids are basal to all extant species. We also examined the origin and distribution of porpoises within the context of this phylogenetic framework. Phocoenid phylogeny together with available geologic evidence suggests that the early history of phocoenids was centered in the North Pacific during the middle Miocene, with subsequent dispersal into the southern hemisphere in the middle Pliocene. A cooling period in the Pleistocene allowed dispersal of the southern ancestor of Phocoena sinus into the North Pacific (Gulf of California).
