Latin American Journal of Aquatic Mammals

Incidental mortality of franciscana dolphin (Pontoporia blainvillei) in Argentina

H. L. Cappozzo — 2007-12-31

La Plata River dolphin or franciscana, Pontoporia blainvillei, is an endemic small cetacean of the Southwest Atlantic coast. It is threatened all along its distribution by a sustained high level of incidental mortality in fisheries. Here we assess levels of franciscana bycatch in Argentine waters between 1997 and 2003. We surveyed 18 localities along the coast of the Buenos Aires Province, between General Lavalle (35°06'S, 57°08'W) and Bahía Blanca (Puerto Rosales-Ingeniero White harbour: 38°47'S, 62°16'W). We recorded data on incidental mortality, fishing gears and fishing effort through 209 personal interviews with fishermen. We estimated annual mortality, fishing effort and catch per unit of effort (CPUE) for each locality and period of time. Mortality was caused by gillnets and trawling gears, purse seine nets and shrimper gears. The total mortality estimated for 1997-2000 was 354 dolphins/year (95% CI = 318-392) and 307 dolphins/year (95% CI = 273-343) for 2002-2003. In the entire survey, CPUE of the northern coast of Buenos Aires Province (Bahía Samborombón and Cabo San Antonio) was significantly higher than CPUE for the southern coast (from Mar del Plata to Bahía Blanca estuary). In addition, CPUE of the northern coast decreased significantly throughout the years. This study suggested that even though the gears or fleet behavior changed locally, Buenos Aires Province evidenced an overall mortality relatively constant during the survey. If we consider a minimum of 400 dolphins killed each year in fishing gear and the estimated population values of 15000 individuals for the Argentine coast; mortality represent more than 2% of the Argentine franciscana population, suggesting that it would be subject to decline. Trends in mortality need to be periodically monitored in this area in order to articulate programs of conservation for the species.

The ontogeny of shape disparity in three species of Otariids (Pinnipedia: Mammalia)

D. Sanfelice — 2007-12-31

We 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.

Age estimation in giant otters (Pteronura brasiliensis) (Carnivora: Mustelidae) using growth layer groups in canine teeth

G. C. Oliveira — 2007-12-31

The 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.

Activity budgets and distribution of bottlenose dolphins (Tursiops truncatus) in the Patos Lagoon estuary, southern Brazil

P. H. Mattos — 2007-12-31

The 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.

Prey occurrence in the stomach contents of four small cetacean species in Peru

I. García-Godos — 2007-12-31

The 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.

Veterinary treatment of an injured wild franciscana dolphin calf (Pontoporia blainvillei, Gervais & d‘Orbigny, 1844)

P. Baldassin — 2007-12-31

An interaction between a juvenile Clymene dolphin (Stenella clymene) and seismic survey vessel M/V Ramform Challenger -PGS, Bacia de Santos, Brazil

M. F. Fernandes — 2007-12-31

Observation of a blue whale (Balaenoptera musculus) feeding in coastal waters of Ecuador

F. Félix — 2007-12-31

Presence and re-sighting of southern elephant seal, Mirounga leonina (L. 1758), on the north-central coast of Chile

M. Sepúlveda — 2007-12-31

Marine protected areas in South America: spatial assessment of cetacean distribution coverage

A. Gómez — 2007-12-31