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and are used to remove sediment when searching for prey. While on land, walrus forelimbs support the trunk by placing the digits flat and bending the wrist at a right angle. This bent forelimb morphology makes terrestrial locomotion awkward. Otariid pinnipeds (English, 1976, 1977) have elongated and thin flippers that flap like a bird wing to produce thrust underwater, and are used to support the trunk on land. Phocid forelimbs function solely in steering while underwater but are usually held flush with the body wall, and are not a significant source of propulsion. On land, most phocids do not use their forelimbs as a weight-bearing appendage. Walrus (Odobenus) flippers are short compared to other pinnipeds, but are very broad and have tiny nails on the dorsal surface. Otariids have elongate and thin flippers with a slight crescent of skin at the ends of each digit. Phocid flippers are divided between some of the digits, and long thin nails extend beyond the dorsal surface of all five digits. The digits of pinnipeds also have unique characteristics (Howell, 1930). All pinnipeds have elongated the digits by developing bars of cartilage at the ends of each digit (Fig. 1C,D). These cartilaginous extensions are longest in otariids, slightly shorter in the walrus and shortest in some phocids. Metacarpal I is longer and thicker than metacarpal II in all pinnipeds except phocines. Pinnipeds also display large and complex forelimb muscles. The walrus has large and powerful muscles, with relatively the same sized muscle bellies as otariids. Otariids isolate more than half of the forelimb musculature in the proximal portion of the forelimb. The triceps muscle complex is relatively large, and allows for elbow retraction. Muscles acting on the otariids wrist create palmar flexion, which is the main source of propulsion. Otariids also have muscles acting on the digits: interossei, digital abductors and adductors, and in some specimens a single lumbrical. Phocids have an enlarged triceps muscle complex. The earliest fossil pinniped, Enaliarctos mealsi, already had forelimbs modified as flippers.
B. Sea Otters Sea otters (Enhydra) do not use their forelimbs while swimming. The forelimbs are specialized in movements requiring great dexterity: prey manipulation, grooming, and caring for young (Howard, 1973). Sea otter forelimbs are small and retractable claws extend from each of the digits. The digits cannot act individually as they are connected by soft tissue webbing. Thick pads line the palmar surfaces of digits. Forelimb musculature is well developed. The giant extinct sea otter Enhydritherium was propelled by its forelimbs, but modern sea otters are pelvic paddlers with enlarged hindlimbs.
C. Polar Bears Polar bears are not only powerful swimmers but also walk on ice or land. The forelimbs are incredibly strong and are the main sources of propulsion while swimming, killing prey, fighting, and hauling out of the water. Alternating strokes of forelimb flexion generate propulsion while swimming and the hindlimbs trail and remain motionless. While fighting another, polar bears will stand on their hindlimbs, wrap forelimbs around another and bite. To haul out of the water, the polar bear pulls itself mostly out of the water with its strong forelimbs, and uses the hindlimbs after most of the body mass is out of the water. While walking on ice or land, polar bears place the whole hand flat on the substrate. Polar bear forelimbs are similar to other bears, except that the scapula has a narrow postscapular fossa. This fossa gives origin to the subscapularis muscle.
See Also the Following Articles HindLimb Anatomy n Musculature n Skeleton
References Benke, H. (1993). Investigations on the osteology and the functional morphology of the flipper of whales and dolphins (Cetacea). Invest. Cetacea 24, 9–252. English, A.W.M. (1976). Functional anatomy of the hands of fur seals and sea lions. Am. J. Anat. 147, 1–17. English, A.W.M. (1977). Structural correlates of forelimb function in fur seals and sea lions. J. Morphol. 151, 325–352. Gordon, K.R. (1981). Locomotor behavior of the walrus (odobenus). J. Zool. London 195, 349–357. Hartman, D.S. (1979). “Ecology and behavior of the manatee (Trichechus manatus).” American Society of Mammalogists, Special Publication No. 5. Howard, L.D. (1973). Muscular anatomy of the forelimb of the sea otter (Enhydra lutris). Proc. Cal. Acad. Sci. XXXIX, 411–500. Howell, A.B. (1930). “Aquatic Mammals: Their Adaptations to Life in the Water”. Charles C. Thomas Press, Springfield. Jacobsen, J.K. (2007). Radiographs from the Humboldt State University Vertebrate Museum. Humboldt, California. Murie, J. (1872). On the structure of the manatee (Manatus americanus). Trans. Zool. Soc. London 8, 127–202. Wang, A., Yuan, L., Rossiter, S.J., Zuo, X., Ru, B., Zhong, H., Han, N., Jones, G., Jepson, P.D., and Zhang, S. (2008). Adaptive evolution of 5′HoxD genes in the origin and diversification of the cetacean flipper. Mol. Biol. Evol. 26, 613–622. Woodward, B.L., Winn, J.P., and Fish, F.E. (2006). Morphological specializations of baleen whales associated with hydrodynamic performance and ecological niche. J. Morphol. 267, 1284–1294. Uhen, M.D. (2004). Form, function, and anatomy of Dorudon atrox (Mammalia, Cetacea): An archaeocete from the middle to late Eocene of Egypt. Univ. Mich., Pap. Paleontol. 34, 1–222.
FRANCISCANA DOLPHIN Pontoporia blainvillei Enrique A. Crespo I. Characteristics and Taxonomy Franciscana (Pontoporia blainvillei) is also known as the La Plata River dolphin. In Uruguay and Argentina it is called franciscana, whereas in Brazil it is called toninha, cachimbo, or boto amarelo. Although both these species and the Yangtze river dolphin, Lipotes vexillifer, were until recently regarded as of the family Pontoporiidae, the franciscana is now the sole member of this family. The franciscana is the only one of the five river dolphins living in the marine environment. It is one of the smallest dolphins and has an extremely long and narrow beak and a bulky head. The franciscana is brownish to dark gray above, turning lighter to the flanks and belly (Figs 1 and 2). The number of teeth in the upper and lower jaws ranges from 53 to 58 and from 51 to 56, respectively.
A. Fossil Record Three records have been related to the franciscana and assigned to the family Pontoporiidae: Brachidelphis mazeasi, a middle Miocene fossil from the Pisco Formation (Perú), Pontistes rectifrons, a late Miocene fossil found in the Paraná Formation (Argentina), and Pliopontos littoralis, a pliocene fossil closely related to the living species described from
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F Figure 1 Franciscana dolphin, Pontoporia blainvillei (Illustrations by Uko Gorter).
Figure 2 Franciscana dolphin (Photo by Projeto Toninhas/ UNIVILLE). the Pisco Formation (Perú) (Barnes, 1985; Cozzuol, 1996; Muizon, 1988). A new species, B. jahuayensis, sp. nov., was recorded from several late Miocene localities of Peru and Chile. It differs mostly from B. mazeasi in its longer snout and higher tooth count. The inclusion of B. jahuayensis will make clearer the phylogeny of the diversified family Pontoporiidae (Lambert and De Muizon, 2013).
B. Geographic Variation Skull morphology, genetic markers, and parasites have been used to identify stocks. The existence of two potential populations was tested by means of the differences in skull morphology. A northern (smaller) form was proposed between Rio de Janeiro and Santa Catarina (Brazil) and a southern (larger) form for Rio Grande do Sul (Brazil), Uruguay, and Argentina (Pinedo, 1991; Barreto and Rosas, 2006). The existence of differences between populations was confirmed some years later, using mtDNA from samples collected at Rio de Janeiro and Rio Grande do Sul (Secchi et al., 1998). It was found that six exclusive haplotypes
were present in the northern population and five in the southern one, indicating some degree of segregation between the stocks. Recent work on mtDNA, microsatellite markers, and radio tracking carried out at Bahía Samborombón and Bahía Anegada (Argentina) reveal significant genetic division at the regional level, fine-scale structure within the study area, limited movement patterns, a small home range, and a high degree of isolation (Bordino et al., 2007; Mendez et al., 2010) suggesting the existence of at least three subpopulations in Argentina (Méndez et al., 2007). More recent findings based on mtDNA indicate a deep evolutionary break between franciscanas from the northern and southern portion of the species distribution, indicating that they must be managed as two ESUs (Cunha et al., 2014). The most likely scenario indicates the existence of five franciscana populations (from south to north): (1) Argentina + Uruguay + Rio Grande do Sul, (2) Santa Catarina + Parana + southern and central Sao Paulo, (3) northern Sao Paulo + southern Rio de Janeiro, (4) northern Rio de Janeiro, and (5) Espirito Santo, of which (4) and (5) are the genetically most differentiated. Gastrointestinal parasites were also used as bioindicators to study the existence of stocks (Aznar et al., 1995). The parasites seem to indicate segregation into two functional or ecological stocks between southern Brazil–Uruguay and Argentina. Three species of parasites were recommended as biological tags (Synthesium pontoporiae, Corynosoma cetaceum, and Anisakis typica) (Andrade et al., 1997). On the basis of the present information, at least three stocks or populations could exist. In the case of S. pontoporiae, preliminary data on infection levels corroborated the putative stock subdivision proposed by Secchi et al. (2003) for the franciscana. However, a later survey of S. pontoporiae based on a greater host sample size, together with a phylogeographic analysis of this digenean trematode, did not provide further supporting evidence for this stock structure (Marigo et al., 2015).
II. Distribution and Abundance The species is endemic in southwestern Atlantic waters. Based on the distribution of sightings and catches, the franciscana lives in a narrow strip of coastal waters beyond the surf to the 30-m isobath
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prey of the franciscana, are typically associated with those continental runoffs and the influence of subtropical shelf waters. The franciscana feeds mostly near the bottom on fishes of several families, such as sciaenids, engraulids, batrachoidids, gadids, carangids, and atherinids. However, sciaenids account for most of the fish species. The diet also includes squids, octopus, and shrimps (Pinedo, 1982). The franciscana feeds on the most abundant species in the region and seems to change its diet according to seasonal prey fluctuations. A comparison of results between two studies carried out 15 years apart in Rio Grande do Sul showed shifts in prey composition in which important prey of the former period were depleted in artisanal fisheries (Bassoi, 1997). Among predators, remains of franciscanas were found in stomach contents of killer whales (Orcinus orca) and several species of sharks.
IV. Behavior and Physiology
F Figure 3 Franciscana dolphin distribution. Adapted by Nina Lisowski from Jefferson, T.A., Webber, M.A., and Pitman, R.L. (2015). “Marine Mammals of the World: A Comprehensive Guide to Their Identification,” 2nd ed. Elsevier, San Diego, CA. (Fig. 3). The complete range known for the franciscana extends from Itaúnas (18°25′S, 39°42′W) in Espirito Santo, Brazil, to the northern coast of Golfo San Matías (41°10′S) in northern Patagonia, Argentina (Crespo et al., 1998). Two gaps are found near the northern range of the species, one between Espírito Santo and Rio de Janeiro and another between Rio de Janeiro and São Paulo (Siciliano et al., 2002, 2015). Recent surveys carried out in Argentina showed that franciscana is also found up to the 50-m isobath (Crespo et al., 2010). However, density declines with distance from the coast. In the strip between the 30- and the 50-m isobaths, density is half that between the coast and the 30-m isobath. Abundance has been estimated for all franciscana management areas (FMAs), mostly through aerial surveys. A first survey was carried out at Rio Grande do Sul State coast, southern Brazil, a region where there are current data on annual incidental mortality. The density was estimated to be 0.657 dolphins/ km2, with a population estimation of 42,000 individuals in 64,000 km2 between the coast and the 30-m isobath. A second survey estimated 6800 individuals (CV = 0.32) in 2004 (Danilewicz et al., 2010). In Argentina, the second area where the franciscanas were surveyed, density was lower than in southern Brazil (0.304–0.377 dolphins/ km2) and abundance was estimated to be 15,000 individuals between the coast and the 50-m isobath in 50,000 km2. Danilewicz et al. (2012) reported that the franciscana population in northern Rio de Janeiro in 2011 was less than 2000 dolphins (CV = 0.46). This is the smallest and lowest density of all franciscana populations for which estimates are available. Abundance estimates for Espírito Santo are required.
III. Ecology Little is known about the northern stock or population between Espirito Santo and Santa Catarina, a region that is under the influence of the Brazil tropical current. Between southern Brazil and Golfo San Matías, the franciscana lives in a transition zone in which the surface circulation of the southwestern Atlantic is dominated by the opposing flows of subtropical and subantarctic water masses. The coastal marine ecosystem is characterized by continental runoffs with a high discharge of high-nutrient river flows (e.g., Lagoa dos Patos, Río de la Plata). Juvenile sciaenids, the most important
Very little is known about the behavior of free-ranging franciscanas, in part because they are difficult to observe in the wild and in part as a consequence of low sighting effort. The franciscana was thought to be solitary or not gregarious. However, herd size may range from 2 to 15 individuals. In aerial surveys carried out in southern Brazil with the objective of estimating abundance, 37 sightings gave a mean herd size of 1.19 (SD: 0.47, range: 1–3). In aerial surveys conducted in Argentina, 101 franciscanas were observed in 71 sightings with an average of 1.43 (SD: 0.85, range: 1–5) individuals per group. A study of wild behavior at Bahía Anegada in southern Buenos Aires Province showed a seasonal pattern with cooperative feeding, with traveling activities increasing during winter and high tide. There is also some evidence of high levels of residence and longer-term associations between individuals (Wells et al., 2013). The mean swimming speed was estimated at 1.3 m/s (±0.09) with a maximum of 1.8 m/s, and mean dive duration was estimated at 21.7 s (±19.2) (range from 3 to 82 s). The average at the surface was estimated to be 1.2 s (Bordino et al., 1999).
V. Life History Females are larger than males. Adult females range between 137 and 177 cm in total length, whereas males range between 121 and 158 cm. The weight of the mature females range between 34 and 53 kg and that of males range between 29 and 43 kg (Kasuya and Brownell, 1979). Neonates in Uruguay range in size between 75 and 80 cm, whereas in southern Brazil they range between 59 and 77 cm (some of the smaller neonates could be near term fetuses). Neonates weigh around 7.3–8.5 kg. Age at sexual maturity is estimated to be 2.7 years, and the gestation period is between 10.5 and 11.1 months. Females give birth around November and lactation lasts for 9 months (Brownell, 1975; Kasuya and Brownell, 1979; Danilewicz et al., 2004). However, calves take solid food around the third month, sizing between 77 and 83 cm. Mating seems to occur in January and February (Brownell, 1984). The calving interval is around 2 years; nevertheless, few females are lactating and pregnant at the same time. Reproductive capacities and life span are low for the species, which is a problem for the population to sustain the mortality rates caused by fisheries. Longevity has been estimated to be close to 15 years for males and 21 for females, fairly low when compared to most of the small cetaceans. Few individuals attain ages over 10 years. Three types of acoustic signals have been recorded, including low, high, and ultrahigh frequency clicks (Busnel et al., 1974). A study in the Rio Negro Estuary, Argentina, recorded 357 min and analyzed 1019 echolocation signals. The clicks had a peak frequency at 139 kHz, and a bandwidth of 19 kHz, ranging from 130 to 149 kHz (Melcón et al., 2012).
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VI. Interactions With Humans Incidental catches in gillnets, mostly of juvenile individuals, is the most serious problem for the species throughout its distribution range, probably since the end of World War II. At that time, many artisanal fisheries for sharks developed in the region for Vitamin A production, which was exported to Europe. During the 1970s, gillnet mortality in Uruguay was estimated at above 400 individuals/ year and fell to around 100 individuals/year in the last few years for economic reasons (Praderi et al., 1989; Pinedo et al., 1989; Corcuera et al., 1994). Nevertheless, minimum mortality rates were always estimated at several thousands of individuals throughout the distribution range. At present, higher mortality rates are shown by the fisheries at Rio Grande do Sul and Buenos Aires Province, where no less than 700–1000 and 500–800 are, respectively, incidentally taken (Pérez Macri and Crespo, 1989; Secchi et al., 1997). The estimated mortality for the whole distribution range could be around 1200–1800 individuals per year. Due to the variability found in mortality rates and abundance estimates, it is not known if those mortality rates are sustainable. In gross numbers, the upper limits of abundance estimations cannot account for the lowest estimates of mortality. Therefore, more precise estimates are needed along with conservation measures to preserve the species. Population viability analysis using data on abundance, bycatch, and population growth suggested that levels of bycatch were not sustainable in all FMAs in the early 2000s (Secchi and Fletcher, 2004). These analyses led to the classification of the franciscana as vulnerable in the IUCN red list (Reeves et al., 2008). Abundance estimates obtained in the late 2000s showed a similar pattern, with bycatch levels ranging from 3% to 6% of the population size in all FMAs for which information is available (Crespo et al., 2010; Zerbini et al., 2010; Danilewicz et al., 2012). Other threats to the franciscana include habitat degradation. A large proportion of the distribution range is subject to pollution from several sources, especially the agricultural use of land and heavy industries between São Paulo in Brazil and Bahía Blanca in Argentina. The coastal zone is also intensely used for boat traffic, tourism, and artisanal and industrial fishing operations.
References Andrade, A., Pinedo, M.C., and Pereira, Jr., J. (1997). The gastrointestinal helminths of the franciscana, Pontoporia blainvillei, in southern Brazil. Rep. Int. Whal. Comm. 47, 669–674. Aznar, F.J., Raga, J.A., Corcuera, J., and Monzón, F. (1995). Helminths as biological tags for franciscana (Pontoporia blainvillei) (Cetacea, Pontoporiidae) in Argentinian and Uruguayan waters. Mammalia 59, 427–435. Barnes, L.G. (1985). Fossil pontoporiid dolphins (Mammalia: Cetacea) from the Pacific Coast of North America. Cont. Sci. Nat. Hist. Mus. Los Angeles County 363, 1–34. Barreto, A.S., and Rosas, F.C.W. (2006). Comparative growth analysis of two populations of Pontoporia blainvillei on the Brazilian coast. Mar. Mamm. Sci. 22, 644–653. Bassoi, M. (1997). Avaliação da dieta alimentar de toninha, Pontoporia blainvillei (Gervais and D’Orbigny, 1844), capturadas acidentalmente na pesca costeira de emalhe no sul do Rio Grande do Sul. Dissertação de Bacharelado. Fundação Universidade do Rio Grande, Rio Grande-RS, 68pp. Bordino, P., Thompson, G., and Iñiguez, M. (1999). Ecology and behaviour of the franciscana dolphin Pontoporia blainvillei in Bahía Anegada, Argentina. J. Cetacean Res. Manag. 1, 213–222. Bordino, P., Wells, R.S., and Stamper, M.A. (2007). Site Fidelity of Franciscana Dolphins Pontoporia blainvillei off Argentina. Abstract accepted at 17th Biennial Conference on the Biology of Marine Mammals, South Africa.
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Brownell Jr., R.L. (1975). Progress report on the biology of the franciscana dolphin Pontoporia blainvillei in Uruguayan waters. J. Fish. Res. Board Can. 32, 1073–1078. Brownell Jr., R.L. (1984). Review of reproduction in platanistid dolphins. Rep. Int. Whal. Comm. (Special Issue 6), 149–158. Busnel, R.G., Dziedzic, A., and Alcuri, G. (1974). Études préliminaires de signaux acoustiques du Pontoporia blainvillei Gervais et D’Orbigny (Cetacea, Platanistidae). Mammalia 38, 449–459. Corcuera, J., Monzón, F., Crespo, E.A., Aguilar, A., and Raga, J.A. (1994). Interactions between marine mammals and coastal fisheries of Necochea and Claromecó (Buenos Aires Province, Argentina). Rep. Int. Whal. Comm. (Special Issue 15), 283–290. Cozzuol, M.A. (1996). Contributions of southern South America to vertebrate paleontology. Münchner Gewissensch. Abh. 30, 321–342. Crespo, E.A., Harris, G., and Gonzalez, R. (1998). Group size and distributional range of the franciscana Pontoporia blainvillei. Mar. Mamm. Sci. 14, 845–849. Crespo, E.A., Pedraza, S.N., Grandi, M.F., Dans, S.L., and Garaffo, G. (2010). Abundance estimation of Franciscana dolphins (Pontoporia blainvillei) in argentine waters and implications for the conservation of the species. Mar. Mamm. Sci 26(1), 17–35. Cunha, H.A., Medeiros, B.V., Barbosa, L.A., Cremer, M.J., Marigo, J., Lailson-Brito, J., Azevedo, A.F., and Sole-Cava, A.M. (2014). Population Structure of the Endangered Franciscana Dolphin (Pontoporia blainvillei): Reassessing Management Units. PLoS One 9(1), e85633. Danilewicz, D., Claver, J.A., Pérez Carrera, A.L., Secchi, E.R., and Fontoura, N.F. (2004). Reproductive biology of male franciscanas (Pontoporia blainvillei) (Mammalia: Cetacea) from Rio Grande do Sul, southern Brazil. Fish. Bull. 102, 581–592. Danilewicz, D., Moreno, I.B., Ott, P.H., Tavares, M., Azevedo, A.F., Secchi, E.R., and Andriolo, A. (2010). Abundance estimate for a threatened population of franciscana dolphins in southern coastal Brazil: uncertainties and management implications. J. Mar. Biol. Assoc. UK 90, 1649–1657. Danilewicz, D., Zerbini, A.N., Andriolo, A., Secchi, E.R., Sucunza, F., Ferreira, E., Denuncio, P., and Flores, P.A.C. (2012). Abundance and distribution of an isolated population of franciscana dolphins (Pontoporia blainvillei) in southeastern Brazil: Red alert for FMA I? Document SC/64/SM17 presented to the IWC Scientific Committee. Panamá Kasuya, T., and Brownell, Jr., R.L. (1979). Age determination, reproduction and growth of franciscana dolphin Pontoporia blainvillei. Sci. Rep. Whales Res. Inst. 31, 45–67. Lambert, O., and de Muizon, C. (2013). A new long-snouted species of the miocene pontoporiid dolphin brachydelphis and a review of the mio-pliocene marine mammal levels in the Sacaco Basin, Peru. J. Vertebr. Paleontol. 33(3), 709–721. Marigo, J., Cunha, H.A., Bertozzi, C.P., Souza, S.P., Rosas, F.C.W., Cremer, M.J., Barreto, A.S., Oliveira, L.R., de Cappozzo, H.L., Valente, A.L.S., Santos, C.P., and Vicente, A.C.P. (2015). Genetic diversity and population structure of Synthesium pontoporiae (Digenea, Brachycladiidae) linked to its definitive host stocks, the endangered Franciscana dolphin, Pontoporia blainvillei (Pontoporiidae) off the coast of Brazil and Argentina. J. Helmint. 89, 19–27. Melcón, M.L., Failla, M., and Iñíguez, M.A. (2012). Echolocation behavior of franciscana dolphins (Pontoporia blainvillei) in the wild. J. Acoust. Soc. Am. 131(6) doi.10.1121/1.4710837. Méndez, M., Rosenbaum, H.C., and Bordino, P. (2007). Conservation genetics of the franciscana dolphin in Northern Argentina: Population structure, by-catch impacts, and management implications Conserv. Genet. Mendez, M., Rosenbaum, H., Yackulic, C., Subramaniam, A., and Bordino, P. (2010). Isolation by environmental distance in mobile marine species: Molecular ecology of franciscana dolphins at their southern range. Mol. Ecol. 19, 2212–2228.
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Muizon, C. De (1988). Les Vertebrés fossiles de la Formation Pisco (Pérou) Triosieme partie: Les Odontocétes (Ceacea, Mammalia) du Miocene. Recherche sur les Grandes Civilisations, Institut Française d’Etudes Andines. Mémoire 78, 1–244. Pérez Macri, G., and Crespo, A. (1989). Survey of the franciscana, Pontoporia blainvillei, along the Argentine coast, with a preliminary evaluation of mortality in coastal fisheries. In “Biology and Conservation of the River Dolphins” (W. F. Perrin, R. L. Brownell, Jr., K. Zhou, and J. Liu, Eds), pp. 57–63. Occasional Papers of the IUCN Species Survival Commission (SSC) 3. Pinedo, M.C. (1982). Analises dos contudos estomacais de Pontoporia blainvillei (Gervais and D’Orbigny, 1844) e Tursiops gephyreus (Lahille, 1908) (Cetacea, Platanistidae e Delphinidae) na zona estuarial e costeira de Rio Grande, RS, Brasil. M.Sc. Thesis. Universidade do Rio Grande do Sul, Brasil, 95pp. Pinedo, M.C. (1991). Development and variation of the franciscana, Pontoporia blainvillei. Ph.D. Thesis. University of Californa, Santa Cruz, 406pp. Pinedo, M.C., Praderi, R., and Brownell, Jr., R.L. (1989). Review of the biology and status of the franciscana Pontoporia blainvillei. In “Biology and Conservation of the River Dolphins” (W. F. Perrin, R. L. Brownell, Jr., K. Zhou, and J. Liu, Eds), pp. 46–51. Occasional Papers of the IUCN Species Survival Commission (SSC) 3. Praderi, R., Pinedo, M.C., and Crespo, E.A. (1989). Conservation and management of Pontoporia blainvillei in Uruguay, Brazil and Argentina. In “Biology and Conservation of the River Dolphins” (W. F. Perrin, R. L. Brownell, Jr., K. Zhou, and J. Liu, Eds), pp. 52–56. Occasional Papers of the IUCN Species Survival Commission (SSC) 3. Reeves, R.R., Dalebout, M.L., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y., Zerbini, A.N., and Zhou, K. (2008). Pontoporia blainvillei in: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1. www.iucnredlist.org. Secchi, E.R., and Fletcher, D. (2004). Modelling population growth and viability analysis for four franciscana stocks: Effects of stock-specific differences in life traits, fishing bycatch, parameter uncertainty and stochasticity. Technical Document presented at the International Whaling Commission SC/56/SM20. Secchi, E.R., Zerbini, A.N., Bassoi, M., Dalla Rosa, L., Moller, L.M., and Roccha-Campos, C.C. (1997). Mortality of franciscanas, Pontoporia blainvillei, in coastal gillneting in southern Brazil: 1994–1995. Rep. Int. Whal. Comm. 47, 653–658. Secchi, E.R., Wang, J.Y., Murray, B., Roccha-Campos, C.C., and White, B.N. (1998). Populational differences between franciscanas, Pontoporia blainvillei, from two geographical locations as indicated by sequences of mtDNA control region. Can. J. Zool. 76, 1622–1627. Secchi, E.R., Danilewicz, D., and Ott, P.H. (2003). Applying the phylogeographic concept to identify franciscana dolphin stocks: Implications to meet management objectives. J. Cetacean Res. Manag. 5, 61–68. Siciliano, S., Moura, J.F., and Secco, H.K.C. (2015). Considerações sobre a distribuição da toninha (Pontoporia blainvillei, Gervais & d’Orbigny, 1844) na costa centro-norte do estado do Rio de Janeiro, Brasil. pp. 112–117. In: P.H. Ott, C. Domit, S. Siciliano, and P.A.C. Flores, (Eds). Memórias do VII Workshop para a coordenação de pesquisa e conservação de Pontoporia blainvillei (Gervais & d’Orbigny, 1844), 22-24 de outubro de 2010, Florianópolis. Porto Alegre, Brasil. 163 p. [Available at www.pontoporia.org in Portuguese]. Siciliano, S., Di Beneditto, A.P.M., and Ramos, R.M.A. (2002). A toninha, Pontoporia blainvillei (Gervais & d´Orbigny, 1844) do Rio de Janeiro e Espírito Santo, costa sudeste do Brasil: caracterização dos habitas e fatores de isolamento das populações. Bol. Mus. Nac. Zool. 476, 1–15. Wells, R.S., Bordino, P., and Douglas, D.C. (2013). Patterns of social association in the franciscana, Pontoporia blainvillei. Mar. Mamm. Sci. doi.10.1111/mms.12010.
FRASER’S DOLPHIN Lagenodelphis hosei M. Louella L. Dolar Fraser’s dolphin belongs to the family Delphinidae. It was described in 1956 based on a skeleton collected by E. Hose from a beach in Sarawak, Borneo in 1895. F.C. Fraser gave it the genus name Lagenodelphis, due to what appeared to him a similarity of the skull to those of Lagenorhynchus spp. and D. delphis. The external appearance of this species was not known until 1971 when specimens were found in widely separated areas: near Cocos Island in the eastern tropical Pacific, South Africa, and southeastern Australia (Perrin et al., 1973).
I. Characteristics and Taxonomy Fraser’s dolphin is easily identified by its stocky body, short but distinct beak, small, triangular, or slightly falcate dorsal fin and small flippers and flukes (Figs 1 and 2; Jefferson et al., 2015). The back is brownish gray, the lower side of the body is cream colored, and the belly is white or pink. The color pattern and other characteristics vary with age and sex. For example, a distinct black head stripe or “bridle” is absent in calves, variable in females, and extensive in adult males, where it merges with the eye-to-anus stripe to form a “bandit mask” (Jefferson et al., 1997). The dorsal fin is slightly falcate in calves and females and more erect or forward canted in adult males. Similarly, the postanal hump is either absent or slight in females and young of both sexes and well developed in adult males. The largest male recorded was 2.7 m long and the largest female 2.6 m, with males over 10 years old significantly larger than females. Large males can weigh up to 210 kg. Fraser’s dolphin belongs to the subfamily Delphininae. Based on cytochrome b mtDNA and short wavelength sensitive (SWS) opsin gene sequences, it is more closely related to Stenella, Tursiops, Delphinus, and Sousa than it is to Lagenorhynchus (LeDuc et al., 1999, Koito et al., 2010). However, the relationship of Lagenodelphis within the delphinines is uncertain (Kingston et al., 2009, Perrin et al., 2013). Morphologically, the skull structure shows close similarity with those of the dolphins Delphinus delphis, Stenella longirostris, and S. coeruleoalba.
II. Distribution and Abundance Fraser’s dolphin is a tropical species, largely distributed between 30°N and 30°S (Fig. 3), but distribution may extend to subtropical waters; new sightings have been reported around the Azores (36°–37°N) (Gomes-Pereira et al., 2013) and strandings recorded in Argentina (~35°S) (So et al., 2009). Strandings outside this limit, such as those in Brittany, United Kingdom (Bones et al., 1998) and Uruguay are unusual, probably influenced by temporary oceanographic events. Density and abundance are known only for a few areas: eastern tropical Pacific, 289,300 (CV 0.34) (Wade and Gerrodette, 1993); eastern Sulu Sea, 13,518 (CV 0.26) and density 0.58/km2 (Dolar et al., 2006); Hawai’i, 10,226 (CV 1.16) and density 0.0042/km2 (Barlow, 2006). Populations in Japan and the Philippines differ morphologically (Perrin et al., 2003).
III. Ecology Fraser’s dolphin is typically oceanic, except in places where deep water approaches the coast such as in the Philippines, Indonesia, and Lesser Antilles, where Fraser’s dolphins can be observed within
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and are used to remove sediment when searching for prey. While on land, walrus forelimbs support the trunk by placing the digits flat and bending the wrist at a right angle. This bent forelimb morphology makes terrestrial locomotion awkward. Otariid pinnipeds (English, 1976, 1977) have elongated and thin flippers that flap like a bird wing to produce thrust underwater, and are used to support the trunk on land. Phocid forelimbs function solely in steering while underwater but are usually held flush with the body wall, and are not a significant source of propulsion. On land, most phocids do not use their forelimbs as a weight-bearing appendage. Walrus (Odobenus) flippers are short compared to other pinnipeds, but are very broad and have tiny nails on the dorsal surface. Otariids have elongate and thin flippers with a slight crescent of skin at the ends of each digit. Phocid flippers are divided between some of the digits, and long thin nails extend beyond the dorsal surface of all five digits. The digits of pinnipeds also have unique characteristics (Howell, 1930). All pinnipeds have elongated the digits by developing bars of cartilage at the ends of each digit (Fig. 1C,D). These cartilaginous extensions are longest in otariids, slightly shorter in the walrus and shortest in some phocids. Metacarpal I is longer and thicker than metacarpal II in all pinnipeds except phocines. Pinnipeds also display large and complex forelimb muscles. The walrus has large and powerful muscles, with relatively the same sized muscle bellies as otariids. Otariids isolate more than half of the forelimb musculature in the proximal portion of the forelimb. The triceps muscle complex is relatively large, and allows for elbow retraction. Muscles acting on the otariids wrist create palmar flexion, which is the main source of propulsion. Otariids also have muscles acting on the digits: interossei, digital abductors and adductors, and in some specimens a single lumbrical. Phocids have an enlarged triceps muscle complex. The earliest fossil pinniped, Enaliarctos mealsi, already had forelimbs modified as flippers.
B. Sea Otters Sea otters (Enhydra) do not use their forelimbs while swimming. The forelimbs are specialized in movements requiring great dexterity: prey manipulation, grooming, and caring for young (Howard, 1973). Sea otter forelimbs are small and retractable claws extend from each of the digits. The digits cannot act individually as they are connected by soft tissue webbing. Thick pads line the palmar surfaces of digits. Forelimb musculature is well developed. The giant extinct sea otter Enhydritherium was propelled by its forelimbs, but modern sea otters are pelvic paddlers with enlarged hindlimbs.
C. Polar Bears Polar bears are not only powerful swimmers but also walk on ice or land. The forelimbs are incredibly strong and are the main sources of propulsion while swimming, killing prey, fighting, and hauling out of the water. Alternating strokes of forelimb flexion generate propulsion while swimming and the hindlimbs trail and remain motionless. While fighting another, polar bears will stand on their hindlimbs, wrap forelimbs around another and bite. To haul out of the water, the polar bear pulls itself mostly out of the water with its strong forelimbs, and uses the hindlimbs after most of the body mass is out of the water. While walking on ice or land, polar bears place the whole hand flat on the substrate. Polar bear forelimbs are similar to other bears, except that the scapula has a narrow postscapular fossa. This fossa gives origin to the subscapularis muscle.
See Also the Following Articles HindLimb Anatomy n Musculature n Skeleton
References Benke, H. (1993). Investigations on the osteology and the functional morphology of the flipper of whales and dolphins (Cetacea). Invest. Cetacea 24, 9–252. English, A.W.M. (1976). Functional anatomy of the hands of fur seals and sea lions. Am. J. Anat. 147, 1–17. English, A.W.M. (1977). Structural correlates of forelimb function in fur seals and sea lions. J. Morphol. 151, 325–352. Gordon, K.R. (1981). Locomotor behavior of the walrus (odobenus). J. Zool. London 195, 349–357. Hartman, D.S. (1979). “Ecology and behavior of the manatee (Trichechus manatus).” American Society of Mammalogists, Special Publication No. 5. Howard, L.D. (1973). Muscular anatomy of the forelimb of the sea otter (Enhydra lutris). Proc. Cal. Acad. Sci. XXXIX, 411–500. Howell, A.B. (1930). “Aquatic Mammals: Their Adaptations to Life in the Water”. Charles C. Thomas Press, Springfield. Jacobsen, J.K. (2007). Radiographs from the Humboldt State University Vertebrate Museum. Humboldt, California. Murie, J. (1872). On the structure of the manatee (Manatus americanus). Trans. Zool. Soc. London 8, 127–202. Wang, A., Yuan, L., Rossiter, S.J., Zuo, X., Ru, B., Zhong, H., Han, N., Jones, G., Jepson, P.D., and Zhang, S. (2008). Adaptive evolution of 5′HoxD genes in the origin and diversification of the cetacean flipper. Mol. Biol. Evol. 26, 613–622. Woodward, B.L., Winn, J.P., and Fish, F.E. (2006). Morphological specializations of baleen whales associated with hydrodynamic performance and ecological niche. J. Morphol. 267, 1284–1294. Uhen, M.D. (2004). Form, function, and anatomy of Dorudon atrox (Mammalia, Cetacea): An archaeocete from the middle to late Eocene of Egypt. Univ. Mich., Pap. Paleontol. 34, 1–222.
FRANCISCANA DOLPHIN Pontoporia blainvillei Enrique A. Crespo I. Characteristics and Taxonomy Franciscana (Pontoporia blainvillei) is also known as the La Plata River dolphin. In Uruguay and Argentina it is called franciscana, whereas in Brazil it is called toninha, cachimbo, or boto amarelo. Although both these species and the Yangtze river dolphin, Lipotes vexillifer, were until recently regarded as of the family Pontoporiidae, the franciscana is now the sole member of this family. The franciscana is the only one of the five river dolphins living in the marine environment. It is one of the smallest dolphins and has an extremely long and narrow beak and a bulky head. The franciscana is brownish to dark gray above, turning lighter to the flanks and belly (Figs 1 and 2). The number of teeth in the upper and lower jaws ranges from 53 to 58 and from 51 to 56, respectively.
A. Fossil Record Three records have been related to the franciscana and assigned to the family Pontoporiidae: Brachidelphis mazeasi, a middle Miocene fossil from the Pisco Formation (Perú), Pontistes rectifrons, a late Miocene fossil found in the Paraná Formation (Argentina), and Pliopontos littoralis, a pliocene fossil closely related to the living species described from
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F Figure 1 Franciscana dolphin, Pontoporia blainvillei (Illustrations by Uko Gorter).
Figure 2 Franciscana dolphin (Photo by Projeto Toninhas/ UNIVILLE). the Pisco Formation (Perú) (Barnes, 1985; Cozzuol, 1996; Muizon, 1988). A new species, B. jahuayensis, sp. nov., was recorded from several late Miocene localities of Peru and Chile. It differs mostly from B. mazeasi in its longer snout and higher tooth count. The inclusion of B. jahuayensis will make clearer the phylogeny of the diversified family Pontoporiidae (Lambert and De Muizon, 2013).
B. Geographic Variation Skull morphology, genetic markers, and parasites have been used to identify stocks. The existence of two potential populations was tested by means of the differences in skull morphology. A northern (smaller) form was proposed between Rio de Janeiro and Santa Catarina (Brazil) and a southern (larger) form for Rio Grande do Sul (Brazil), Uruguay, and Argentina (Pinedo, 1991; Barreto and Rosas, 2006). The existence of differences between populations was confirmed some years later, using mtDNA from samples collected at Rio de Janeiro and Rio Grande do Sul (Secchi et al., 1998). It was found that six exclusive haplotypes
were present in the northern population and five in the southern one, indicating some degree of segregation between the stocks. Recent work on mtDNA, microsatellite markers, and radio tracking carried out at Bahía Samborombón and Bahía Anegada (Argentina) reveal significant genetic division at the regional level, fine-scale structure within the study area, limited movement patterns, a small home range, and a high degree of isolation (Bordino et al., 2007; Mendez et al., 2010) suggesting the existence of at least three subpopulations in Argentina (Méndez et al., 2007). More recent findings based on mtDNA indicate a deep evolutionary break between franciscanas from the northern and southern portion of the species distribution, indicating that they must be managed as two ESUs (Cunha et al., 2014). The most likely scenario indicates the existence of five franciscana populations (from south to north): (1) Argentina + Uruguay + Rio Grande do Sul, (2) Santa Catarina + Parana + southern and central Sao Paulo, (3) northern Sao Paulo + southern Rio de Janeiro, (4) northern Rio de Janeiro, and (5) Espirito Santo, of which (4) and (5) are the genetically most differentiated. Gastrointestinal parasites were also used as bioindicators to study the existence of stocks (Aznar et al., 1995). The parasites seem to indicate segregation into two functional or ecological stocks between southern Brazil–Uruguay and Argentina. Three species of parasites were recommended as biological tags (Synthesium pontoporiae, Corynosoma cetaceum, and Anisakis typica) (Andrade et al., 1997). On the basis of the present information, at least three stocks or populations could exist. In the case of S. pontoporiae, preliminary data on infection levels corroborated the putative stock subdivision proposed by Secchi et al. (2003) for the franciscana. However, a later survey of S. pontoporiae based on a greater host sample size, together with a phylogeographic analysis of this digenean trematode, did not provide further supporting evidence for this stock structure (Marigo et al., 2015).
II. Distribution and Abundance The species is endemic in southwestern Atlantic waters. Based on the distribution of sightings and catches, the franciscana lives in a narrow strip of coastal waters beyond the surf to the 30-m isobath
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prey of the franciscana, are typically associated with those continental runoffs and the influence of subtropical shelf waters. The franciscana feeds mostly near the bottom on fishes of several families, such as sciaenids, engraulids, batrachoidids, gadids, carangids, and atherinids. However, sciaenids account for most of the fish species. The diet also includes squids, octopus, and shrimps (Pinedo, 1982). The franciscana feeds on the most abundant species in the region and seems to change its diet according to seasonal prey fluctuations. A comparison of results between two studies carried out 15 years apart in Rio Grande do Sul showed shifts in prey composition in which important prey of the former period were depleted in artisanal fisheries (Bassoi, 1997). Among predators, remains of franciscanas were found in stomach contents of killer whales (Orcinus orca) and several species of sharks.
IV. Behavior and Physiology
F Figure 3 Franciscana dolphin distribution. Adapted by Nina Lisowski from Jefferson, T.A., Webber, M.A., and Pitman, R.L. (2015). “Marine Mammals of the World: A Comprehensive Guide to Their Identification,” 2nd ed. Elsevier, San Diego, CA. (Fig. 3). The complete range known for the franciscana extends from Itaúnas (18°25′S, 39°42′W) in Espirito Santo, Brazil, to the northern coast of Golfo San Matías (41°10′S) in northern Patagonia, Argentina (Crespo et al., 1998). Two gaps are found near the northern range of the species, one between Espírito Santo and Rio de Janeiro and another between Rio de Janeiro and São Paulo (Siciliano et al., 2002, 2015). Recent surveys carried out in Argentina showed that franciscana is also found up to the 50-m isobath (Crespo et al., 2010). However, density declines with distance from the coast. In the strip between the 30- and the 50-m isobaths, density is half that between the coast and the 30-m isobath. Abundance has been estimated for all franciscana management areas (FMAs), mostly through aerial surveys. A first survey was carried out at Rio Grande do Sul State coast, southern Brazil, a region where there are current data on annual incidental mortality. The density was estimated to be 0.657 dolphins/ km2, with a population estimation of 42,000 individuals in 64,000 km2 between the coast and the 30-m isobath. A second survey estimated 6800 individuals (CV = 0.32) in 2004 (Danilewicz et al., 2010). In Argentina, the second area where the franciscanas were surveyed, density was lower than in southern Brazil (0.304–0.377 dolphins/ km2) and abundance was estimated to be 15,000 individuals between the coast and the 50-m isobath in 50,000 km2. Danilewicz et al. (2012) reported that the franciscana population in northern Rio de Janeiro in 2011 was less than 2000 dolphins (CV = 0.46). This is the smallest and lowest density of all franciscana populations for which estimates are available. Abundance estimates for Espírito Santo are required.
III. Ecology Little is known about the northern stock or population between Espirito Santo and Santa Catarina, a region that is under the influence of the Brazil tropical current. Between southern Brazil and Golfo San Matías, the franciscana lives in a transition zone in which the surface circulation of the southwestern Atlantic is dominated by the opposing flows of subtropical and subantarctic water masses. The coastal marine ecosystem is characterized by continental runoffs with a high discharge of high-nutrient river flows (e.g., Lagoa dos Patos, Río de la Plata). Juvenile sciaenids, the most important
Very little is known about the behavior of free-ranging franciscanas, in part because they are difficult to observe in the wild and in part as a consequence of low sighting effort. The franciscana was thought to be solitary or not gregarious. However, herd size may range from 2 to 15 individuals. In aerial surveys carried out in southern Brazil with the objective of estimating abundance, 37 sightings gave a mean herd size of 1.19 (SD: 0.47, range: 1–3). In aerial surveys conducted in Argentina, 101 franciscanas were observed in 71 sightings with an average of 1.43 (SD: 0.85, range: 1–5) individuals per group. A study of wild behavior at Bahía Anegada in southern Buenos Aires Province showed a seasonal pattern with cooperative feeding, with traveling activities increasing during winter and high tide. There is also some evidence of high levels of residence and longer-term associations between individuals (Wells et al., 2013). The mean swimming speed was estimated at 1.3 m/s (±0.09) with a maximum of 1.8 m/s, and mean dive duration was estimated at 21.7 s (±19.2) (range from 3 to 82 s). The average at the surface was estimated to be 1.2 s (Bordino et al., 1999).
V. Life History Females are larger than males. Adult females range between 137 and 177 cm in total length, whereas males range between 121 and 158 cm. The weight of the mature females range between 34 and 53 kg and that of males range between 29 and 43 kg (Kasuya and Brownell, 1979). Neonates in Uruguay range in size between 75 and 80 cm, whereas in southern Brazil they range between 59 and 77 cm (some of the smaller neonates could be near term fetuses). Neonates weigh around 7.3–8.5 kg. Age at sexual maturity is estimated to be 2.7 years, and the gestation period is between 10.5 and 11.1 months. Females give birth around November and lactation lasts for 9 months (Brownell, 1975; Kasuya and Brownell, 1979; Danilewicz et al., 2004). However, calves take solid food around the third month, sizing between 77 and 83 cm. Mating seems to occur in January and February (Brownell, 1984). The calving interval is around 2 years; nevertheless, few females are lactating and pregnant at the same time. Reproductive capacities and life span are low for the species, which is a problem for the population to sustain the mortality rates caused by fisheries. Longevity has been estimated to be close to 15 years for males and 21 for females, fairly low when compared to most of the small cetaceans. Few individuals attain ages over 10 years. Three types of acoustic signals have been recorded, including low, high, and ultrahigh frequency clicks (Busnel et al., 1974). A study in the Rio Negro Estuary, Argentina, recorded 357 min and analyzed 1019 echolocation signals. The clicks had a peak frequency at 139 kHz, and a bandwidth of 19 kHz, ranging from 130 to 149 kHz (Melcón et al., 2012).
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VI. Interactions With Humans Incidental catches in gillnets, mostly of juvenile individuals, is the most serious problem for the species throughout its distribution range, probably since the end of World War II. At that time, many artisanal fisheries for sharks developed in the region for Vitamin A production, which was exported to Europe. During the 1970s, gillnet mortality in Uruguay was estimated at above 400 individuals/ year and fell to around 100 individuals/year in the last few years for economic reasons (Praderi et al., 1989; Pinedo et al., 1989; Corcuera et al., 1994). Nevertheless, minimum mortality rates were always estimated at several thousands of individuals throughout the distribution range. At present, higher mortality rates are shown by the fisheries at Rio Grande do Sul and Buenos Aires Province, where no less than 700–1000 and 500–800 are, respectively, incidentally taken (Pérez Macri and Crespo, 1989; Secchi et al., 1997). The estimated mortality for the whole distribution range could be around 1200–1800 individuals per year. Due to the variability found in mortality rates and abundance estimates, it is not known if those mortality rates are sustainable. In gross numbers, the upper limits of abundance estimations cannot account for the lowest estimates of mortality. Therefore, more precise estimates are needed along with conservation measures to preserve the species. Population viability analysis using data on abundance, bycatch, and population growth suggested that levels of bycatch were not sustainable in all FMAs in the early 2000s (Secchi and Fletcher, 2004). These analyses led to the classification of the franciscana as vulnerable in the IUCN red list (Reeves et al., 2008). Abundance estimates obtained in the late 2000s showed a similar pattern, with bycatch levels ranging from 3% to 6% of the population size in all FMAs for which information is available (Crespo et al., 2010; Zerbini et al., 2010; Danilewicz et al., 2012). Other threats to the franciscana include habitat degradation. A large proportion of the distribution range is subject to pollution from several sources, especially the agricultural use of land and heavy industries between São Paulo in Brazil and Bahía Blanca in Argentina. The coastal zone is also intensely used for boat traffic, tourism, and artisanal and industrial fishing operations.
References Andrade, A., Pinedo, M.C., and Pereira, Jr., J. (1997). The gastrointestinal helminths of the franciscana, Pontoporia blainvillei, in southern Brazil. Rep. Int. Whal. Comm. 47, 669–674. Aznar, F.J., Raga, J.A., Corcuera, J., and Monzón, F. (1995). Helminths as biological tags for franciscana (Pontoporia blainvillei) (Cetacea, Pontoporiidae) in Argentinian and Uruguayan waters. Mammalia 59, 427–435. Barnes, L.G. (1985). Fossil pontoporiid dolphins (Mammalia: Cetacea) from the Pacific Coast of North America. Cont. Sci. Nat. Hist. Mus. Los Angeles County 363, 1–34. Barreto, A.S., and Rosas, F.C.W. (2006). Comparative growth analysis of two populations of Pontoporia blainvillei on the Brazilian coast. Mar. Mamm. Sci. 22, 644–653. Bassoi, M. (1997). Avaliação da dieta alimentar de toninha, Pontoporia blainvillei (Gervais and D’Orbigny, 1844), capturadas acidentalmente na pesca costeira de emalhe no sul do Rio Grande do Sul. Dissertação de Bacharelado. Fundação Universidade do Rio Grande, Rio Grande-RS, 68pp. Bordino, P., Thompson, G., and Iñiguez, M. (1999). Ecology and behaviour of the franciscana dolphin Pontoporia blainvillei in Bahía Anegada, Argentina. J. Cetacean Res. Manag. 1, 213–222. Bordino, P., Wells, R.S., and Stamper, M.A. (2007). Site Fidelity of Franciscana Dolphins Pontoporia blainvillei off Argentina. Abstract accepted at 17th Biennial Conference on the Biology of Marine Mammals, South Africa.
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FRASER’S DOLPHIN Lagenodelphis hosei M. Louella L. Dolar Fraser’s dolphin belongs to the family Delphinidae. It was described in 1956 based on a skeleton collected by E. Hose from a beach in Sarawak, Borneo in 1895. F.C. Fraser gave it the genus name Lagenodelphis, due to what appeared to him a similarity of the skull to those of Lagenorhynchus spp. and D. delphis. The external appearance of this species was not known until 1971 when specimens were found in widely separated areas: near Cocos Island in the eastern tropical Pacific, South Africa, and southeastern Australia (Perrin et al., 1973).
I. Characteristics and Taxonomy Fraser’s dolphin is easily identified by its stocky body, short but distinct beak, small, triangular, or slightly falcate dorsal fin and small flippers and flukes (Figs 1 and 2; Jefferson et al., 2015). The back is brownish gray, the lower side of the body is cream colored, and the belly is white or pink. The color pattern and other characteristics vary with age and sex. For example, a distinct black head stripe or “bridle” is absent in calves, variable in females, and extensive in adult males, where it merges with the eye-to-anus stripe to form a “bandit mask” (Jefferson et al., 1997). The dorsal fin is slightly falcate in calves and females and more erect or forward canted in adult males. Similarly, the postanal hump is either absent or slight in females and young of both sexes and well developed in adult males. The largest male recorded was 2.7 m long and the largest female 2.6 m, with males over 10 years old significantly larger than females. Large males can weigh up to 210 kg. Fraser’s dolphin belongs to the subfamily Delphininae. Based on cytochrome b mtDNA and short wavelength sensitive (SWS) opsin gene sequences, it is more closely related to Stenella, Tursiops, Delphinus, and Sousa than it is to Lagenorhynchus (LeDuc et al., 1999, Koito et al., 2010). However, the relationship of Lagenodelphis within the delphinines is uncertain (Kingston et al., 2009, Perrin et al., 2013). Morphologically, the skull structure shows close similarity with those of the dolphins Delphinus delphis, Stenella longirostris, and S. coeruleoalba.
II. Distribution and Abundance Fraser’s dolphin is a tropical species, largely distributed between 30°N and 30°S (Fig. 3), but distribution may extend to subtropical waters; new sightings have been reported around the Azores (36°–37°N) (Gomes-Pereira et al., 2013) and strandings recorded in Argentina (~35°S) (So et al., 2009). Strandings outside this limit, such as those in Brittany, United Kingdom (Bones et al., 1998) and Uruguay are unusual, probably influenced by temporary oceanographic events. Density and abundance are known only for a few areas: eastern tropical Pacific, 289,300 (CV 0.34) (Wade and Gerrodette, 1993); eastern Sulu Sea, 13,518 (CV 0.26) and density 0.58/km2 (Dolar et al., 2006); Hawai’i, 10,226 (CV 1.16) and density 0.0042/km2 (Barlow, 2006). Populations in Japan and the Philippines differ morphologically (Perrin et al., 2003).
III. Ecology Fraser’s dolphin is typically oceanic, except in places where deep water approaches the coast such as in the Philippines, Indonesia, and Lesser Antilles, where Fraser’s dolphins can be observed within