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ArtículoVariation in Dorsal Fin Morphology in Common Bottlenose Dolphin Tursiops truncatus (Cetacea: Delphinidae) Populations from the Southeast Pacific Ocean(International Whaling Commission, 2017)We succinctly summarize population ID information for common bottlenose dolphins Tursiops truncatus of the Pacific coast of South America, covering four coastal range states. Phylogenetic uncertainties relate primarily to offshore vs. coastal (inshore) ecotypes and biogeographic borders between the five proposed populations (2 offshore, 3 coastal): Colombia-Ecuador Offshore stock (probably = ETP Offshore), Peru-Chile Offshore, Ecuador Coastal, Peru Coastal and an unique community (Pod-R) on the north-central coast of Chile. Main questions concern the extent of gene flow between the offshore stocks at one hand, and with -and between- the three coastal populations at the other hand. Seven cranial characters, four non-metric (separation of occipital condyles, pterygoid bone development, exostosis of periotic) and three metric (tooth width, antorbital process length, maximum width palatines), dorsal fin shape, body stockiness, mt-DNA (control region), habitat, prey composition, parasite load, behaviour and prevalence of some infectious diseases differentiate coastal from offshore forms. 'Pod-R' is the southernmost (29°15'S) and only confirmed coastal form community in Chilean waters, albeit with an offshore (falcate) dorsal fin. Bottlenose dolphins which regularly transit nearshore in the Lagos and Aysén regions (Chilean Patagonia) and occasionally enter deep fjords, present an offshore morphotype. We suggest that two other coastal areas in Chile where bottlenose dolphins have been documented over decades, one a ca. 60 km stretch of coastline centered at Valparaiso/Laguna Verde (33°10'S) in central Chile, and a 190 km coastline around the Mejillones Peninsula (23°10'S) in northern Chile, may not host coastal but offshore form animals. The continental border of the Atacama Trench off northern and northcentral Chile leaves an extremely narrow, steep shelf with nearshore deep water, locally with strong coastal upwelling and increased productivity. This habitat seems to attract oceanic cetaceans, including offshore T. truncatus, sperm whales, large balaenopterids, and other species. The southern distribution range of true coastal morphotype bottlenose dolphins in Pacific South America remains unknown but off Chile distance-to-shore may not be the reliable indicator of ecotype as it is further north in the study region.
ArtículoCommon bottlenose dolphins Tursiops truncatus of Pacific South America, a synoptic review of population identification data(International Whaling Commission, 2017)Variation in dorsal fin morphology was assessed in five bottlenose dolphin (Tursiops truncatus) populations from the Southeast Pacific. We hypothesized that habitat specialization between coastal and offshore ecotypes led to differences in dorsal fin morphology. Photographs and direct measurements of dorsal fins were used to calculate three indexes: height/length base (h/b), width at half height/length base (a/b) and overhang of the dorsal fin tip/length base (falcateness) (s/b). The sample included 163 individuals (129 coastal and 34 offshore) from Ecuador, 60 individuals (9 coastal and 51 offshore) from Peru and 25 individuals of an inshore form from northcentral Chile (Pod-R). Values were logarithmically transformed to allow one-way ANOVAs and t-tests. Ontogenetic variation was found in coastal dolphins from Ecuador, with indices significantly different among age/classes. All indices were higher in juveniles and calves, suggesting a stronger (allometric) growth of the dorsal fin base (b) than in the upper parts of the fin. Hence only adults and subadults were considered in further analysis. Statistically significant differences were found in h/b and a/b indices between coastal specimens from Ecuador and Peru, and between offshore specimens from Ecuador and Peru, and Pod-R. Offshore and Pod-R data were pooled and compared with coastal specimens from Ecuador and Peru; significant differences were found in indices h/b and s/b. Offshore dorsal fins are relatively higher than coastal fins. However the most consistent and visible difference between ecotypes was the strong falcateness (high s/b) in the offshore forms vs. a more triangular shape (low s/b) in coastal forms. Except one outlier, all other cases could be correctly classified through ocular inspection by experienced observers. Chile's Pod-R represents a unique case of an inshore form with strong falcateness, a typical offshore trait. Ecuadorian offshore form showed highest relative dorsal fin height (h/b), followed by Peruvian coastal form, Pod-R, Peruvian offshore and, lowest, Ecuadorian coastal. Relative fin width at mid-height (a/b) was widest in Peruvian coastal stock, followed by Ecuadorian offshore, Peruvian offshore, Ecuadorian coastal and narrowest in Chilean Pod-R. The latter had also the highest falcateness index of all groups, consistent with their extremely falcate dorsal fins. Extreme values for two of three indices agree with marked molecular differences between Pod-R dolphins and Peruvian dolphins and, to a lesser degree, Chilean offshore. Pod-R may represent a recent radiation into the coastal environment from offshore ancestors, a sort of 'transitional form'. High falcateness may be retained due to particularities of the local environment, e.g. fairly deep water.