Latin American Journal of Aquatic Mammals (LAJAM)
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The ontogeny of shape disparity in three species of Otariids (Pinnipedia: Mammalia)
No full textWe compared skull ontogenies in three otariid species to identify evolutionary novelties and to understand their relationships with diversity. The species studied were Arctocephalus australis, Callorhinus ursinus and Otaria byronia. We analyzed evolutionary changes in three parameters of developmental trajectories of skull shape: shape at the outset of ontogeny, allometric pattern, and the amount of change undergone over the course of ontogeny, which depends on its duration (the length of the ontogenetic vector) and on the rate of development. Initial shapes were always very different among the species and the distances between shapes increased with time, independently from size. Furthermore, when the complete samples were considered, all the ontogenetic trajectories were significantly different concerning the directions of the allometric vectors during ontogeny. Ontogenetic trajectories also differed significantly among almost all compared pairs, except for the trajectories of males of A. australis and C. ursinus. However, these differences are expected by chance (considering the range of angles within each sample). A similar pattern was found when the subadults were compared in pairs of species, as well as adult males of A. australis and O. byronia. The correlation found between ontogenies of juveniles was expected by chance, with exception of C. ursinus and O. byronia. The ontogenetic trajectory of C. ursinus, is the shortest and that of O. byronia is the longest, with the latter being near the triple of the former. A. australis has an intermediary length of ontogenetic trajectory. Considering all three species, disparity increased significantly over ontogeny since the disparity of the adults is near double that between juveniles. However, the pattern of disparity did not change considerably during ontogeny. For any ontogenetical stage, O. byronia is the species that most contributed to the disparity of the group, followed by C. ursinus. Finally, ontogenies examined herein are clearly not constrained (almost every developmental parameter of shape that could evolve was observed) and perhaps the differences in patterns have additive effects in the differentiation of the ontogenies
Site fidelity and behaviour of killer whales (Orcinus orca) at Sea Lion Island in the Southwest Atlantic
No full textUsing shore-based observations and photographic identification of killer whales (Orcinus orca) at Sea Lion Island (52°26'S,59°05'W) in the Falklands/Malvinas archipelago, we identified a small group (6 to 12 animals) targeting a southern elephant seal (Mirounga leonina) breeding colony. Sightings during 2004-05 and photographic matches from the early 1990s suggest site fidelity. Behavioural observations revealed ambush and shallow water hunting techniques along rocky outcrops and two beaches used by elephant seal pups and juveniles. A single successful attack and three unsuccessful attempts were recorded
Activity budgets and distribution of bottlenose dolphins (Tursiops truncatus) in the Patos Lagoon estuary, southern Brazil
No full textThe common bottlenose dolphin, Tursiops truncatus, is one of the world's best known cetaceans. However, there are few studies on the activity budgets and distribution of this species along the Brazilian coast. This study aimed at describing and quantifying the behavioral activity of T. truncatus in the Patos Lagoon Estuary, Rio Grande do Sul state, southern Brazil (ca. 32°09'S, 52°05'W). The study area was divided into three sub-areas according to the proximity to the estuary mouth. The behavioral data were gathered every 5 minutes following a focal group sampling approach. A total of 34 boat surveys were conducted between December 2001 and January 2003, totaling 66.95h of direct observation and 672 records of behavioral activities. The first 15 minutes of each group encounter were discarded to avoid the influence of the boat approach on dolphin behavior. The most observed behavior was feeding (37.64%), followed by traveling (29.17%), travel-feeding (21.87%), socializing (5.8%), milling (4.33%) and resting (1.19%). There was not a significant difference among the frequencies of commonly observed behaviors: feeding, traveling and travel feeding (p<0.05, t-test for proportions). Dependence between activity and season was detected in subareas I and II (p<0.001; Pearson's Χ²), as well as an association between activity and sub-areas (p<0.001; Pearson's Χ²). Regarding group size, 56.41% of the activities recorded were carried out by groups of 1 to 3 dolphins, 31.63% from 4 to 6, 10.25% from 7 to 10, and 1.71% by groups with more than 10 individuals. This study confirmed the importance of the Patos Lagoon Estuary as an area for bottlenose dolphins to conduct their daytime activities, in particular feeding
Movement of a humpback whale (Megaptera novaeangliae) between the Revillagigedo and Hawaiian Archipelagos within a winter breeding season
No full textOn 5 February 1986 a humpback whale was photographed near Isla Clarión, in the Revillagigedo Archipelago, Mexico, and again 51 days later near the island of Kauai in the Hawaiian Archipelago. The straight-line distance between the two sightings is approximately 4700km. This resighting constitutes the only known instance in which the same humpback whale has been documented in two discretely different breeding areas within the same season. This finding reinforces the conclusion from other studies that the humpback whale aggregation of the Revillagigedo Archipelago constitutes a separate sub-population from mainland Mexic
Has the manatee (Trichechus manatus) dissapeared from the northern coast of the State of Veracruz, Mexico?
No full textKnowledge about the distribution and abundance of the manatee (Trichechus manatus) along the coast of the Mexican state of Veracruz is scarce. Since few studies have been undertaken in this area, boat-based surveys and interviews with local fishermen were carried out to determine if there are remaining herds of manatees in the vicinity of the coastal towns of Tamiahua, Tuxpan, Tecolutla, and Casitas-Nautla. All of the fishermen interviewed noted that they used to see large herds of manatees in the area. Seventy-four percent (371 fishermen) of the survey respondents had not seen a manatee over the last 10 years, and 26% (131 fishermen) responded that the last time they saw large or small groups of manatees was in 1986 and 1995, respectively. However, since 1996, none of the fishermen had observed any manatees in the area. Similarly, no manatees were observed during the boat-based surveys (effort of approximately 1200km). It is almost certain that anthropogenic influences have altered manatee habitat significantly and thus affected the numbers of animals using the area. Also, fishermen speculated that natural phenomena such as cyclones, flooding, and storms caused manatees to move away from the area. More surveys along the coast of Veracruz are needed to determine if manatees still occur in this Mexican state. Also, it is urgent to implement conservation measures in the northern range of the manatee in Mexico to ensure the survival of this species along its original distribution
Age estimation in giant otters (Pteronura brasiliensis) (Carnivora: Mustelidae) using growth layer groups in canine teeth
No full textThe canines of six giant otters Pteronura brasiliensis (5 males and 1 female) from the zoological collection of the National Institute of Amazonian Research (INPA) were analyzed for age estimation. Of these, two were from known-age individuals of 2 and 5 years. Ages were read counting the Growth Layer Groups (GLGs) observed in thin sections (30μm) of decalcified teeth. GLGs were present in the dentine but were not conspicuous; age estimates were only reliable when counted in the cementum. Periodicity of GLGs and age estimates were calibrated with the known-age individuals. Results revealed an annual deposition pattern of GLGs in the cementum of giant otter canines, and no apparent differences were found in the GLG patterns observed between males and females, or between captive and free-ranging individuals. The youngest and oldest giant otters analyzed were 2 and 20 years old, respectively. These results suggest that the longevity of captive giant otters is around 20 years. The age determination technique applied here proved to be useful for age estimation in giant otters and can contribute as a powerful tool for future studies on the population dynamics of P. brasiliensis, which is currently classified as endangered
Prey occurrence in the stomach contents of four small cetacean species in Peru
No full textThe diets of long-beaked common dolphins Delphinus capensis (n=117), dusky dolphins Lagenorhynchus obscurus (n=72), Burmeister's porpoises Phocoena spinipinnis (n=69) and offshore common bottlenose dolphins Tursiops truncatus (n=22) were determined based on the analysis of the stomach contents collected from animals landed in ports along the Peruvian central coast and from Marcona, in southern Peru, during 1987-1993. The number of prey ingested was obtained by counting the number of fish otoliths and cephalopod mandibles (beaks). Only fish could be identified to species level. Long-beaked common dolphins fed mainly on Peruvian anchovy Engraulis ringens (70.0% by number), Panama lightfish Vincigerria lucetia (7.8%) and slimtail lanternfish Lampanyctus parvicauda (6.7%). Dusky dolphins consumed mainly anchovies (49.7%, 16.8%), slimtail lanternfish (23.6%, 0.1%), Inca scad Trachurus murphyi (17.1%, 0%) and mote sculpin Normanichthys crockeri (0%, 76.0%) off the central Peruvian coast and Marcona, respectively. In the same areas, Burmeister's porpoises fed mainly on anchovy (88.9%, 77.6%), silverside Odontesthes regia (6.5%, 0%), mote sculpin (0%, 8.1%) and South Pacific hake Merluccius gayi (0.6%, 7.9%). Offshore common bottlenose dolphins consumed mainly slimtail lanternfish (39.2%), barracuda Sphyraena sp. (13.5%) and Peruvian pilchard Sardinops sagax (13.3%). The diversity indices of the diet and temporal shifts in the main prey suggest an opportunistic feeding strategy for the four cetacean species studied, which take advantage of the locally most available epipelagic and mesopelagic schooling fish. Cluster analysis shows high similarity in their diets, with these four marine top predators being able to optimally exploit the high productivity of the Peruvian upwelling ecosystem
