Mariano A. Coscarella

Feeding aggregation and aggressive interaction between bottlenose (Tursiops truncatus) and Commerson’s dolphins (Cephalorhynchus commersonii) in Patagonia, Argentina

We report the first recorded interactions between bottlenose dolphin (Tursiops truncatus) and Commerson’s dolphins (Cephalorhynchus commersonii). The diurnal behavioral patterns of bottlenose dolphins in Bahía Engaño, Argentina, were similar to those described for other coastal populations around the world. The majority of the feeding bouts were recorded near the mouth the Chubut River. When not feeding near the river, bottlenose dolphins generally swam along the coast, and interactions with Commerson’s dolphins were recorded very close to the shore on two occasions during a 3-year period. In the first event, both species were feeding on a fish school. The second interaction was aggressive in nature, involving one juvenile and three adult bottlenose dolphins with several Commerson’s dolphins. Two of the adult bottlenose dolphins attacked the Commerson’s dolphins. We propose that the observed behavior represented defense of the juvenile bottlenose dolphin.

Behavior and seasonal variation in the relative abundance of Commerson’s dolphin (Cephalorhynchus commersonii) in northern Patagonia, Argentina

Commerson’s dolphins (Cephalorhynchus commersonii) along the Patagonian coast of South America suffer incidental mortality in fisheries and are the target of a dolphin-watching industry. We describe the daily activity patterns and assess the variation in the relative abundance of the species near the northern boundary of its range. Information was gathered with a spotting scope from a cliff-top vantage point applying the method of scan sampling. Behaviors were categorized as individual feeding, cooperative feeding, directional swimming, socializing, and resting. These behaviors are similar to those observed in other species of small cetacean, but differences were found regarding the patterns of directional swimming and feeding techniques. Hunting tactics favored the association of terns with dolphin groups. No clear dial behavioral pattern was observed, but seasonal changes in the frequency of behaviors were recorded. Group and school sizes were larger during periods with colder sea surface temperature (SST). Seasonal abundance was correlated with SST, suggesting that at higher SST the species forsakes the area, probably in favor of coastal areas to the south with lower SST.

Influence of body size and ranging patterns on delphinid sociality: Associations among Commerson's dolphins

Abstract We investigated the association patterns of 48 identifiable Commersons dolphins (Cephalorhynchus commersonii) photographed 2 or more times over a 2-year period in Bahía Engaño, Chubut, Argentina. The associations among them were not different from random for short time periods (7 days) but were significantly different from random for longer periods. Lagged identification rate and lagged association rate models show that dolphins remained in the area on average 15 days and then moved away as the original groups dissolved. Commersons dolphins appear to have a fission–fusion society, and the observed strength of their associations is in concordance with the predictions regarding their body size and ranging patterns. The dolphins seem to rely on Bahía Engaño as a core area for most of their activities, but the aggregations are labile and some individuals remain associated in a more stable manner with only a few other individuals.

Technique used by killer whales (Orcinus orca) when hunting for dolphins in Patagonia, Argentina

Fil: Coscarella, Mariano Alberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Nacional Patagonico; Argentina. Universidad Nacional de la Patagonia; Argentina

The human dimension of the conflict between fishermen and South American sea lions in southern Brazil

Abstract We analysed the fishermen’s perceptions on the South American sea lions (Otaria flavescens) and its interactions with the local fishery close to the Wildlife Refuge of Ilha dos Lobos, a marine protected area in southern Brazil. Sea lions prey upon the same resources targeted by the fishermen. They repeatedly hunt on the nets and consequently damage them. In response, fishermen persecute sea lions. However, in conflicts with high-profile animals, the perceived damage often exceeds the actual evidence. Results from 100 interviews revealed that fishermen’s perception of damage and their attitudes were affected by age, hierarchical position in the crew, if fishing was the only source of income, and level of formal education. Greater perception of damage and more negative attitude were found among older, less educated sailor fishermen who had no other source of income besides fishing. The average fisherman had a relatively good knowledge about sea lions, but also a negative attitude towards them. We recommend actions addressing these negative attitudes through environmental education, with emphasis on adjusting exaggerated perceptions of impact and the potential of the species for wildlife tourism, as a vital step towards the conciliation of sustainable fisheries and O. flavescens conservation in the Brazilian coast.

Development of a site fidelity index based on population capture-recapture data

Background Site fidelity is considered as an animal’s tendency to return to a previously occupied place; this is a component of animal behaviour that allows us to understand movement patterns and aspects related to the animal’s life history. Although there are many site fidelity metrics, the lack of standardisation presents a considerable challenge in terms of comparability among studies. Methods This investigation focused on the theoretical development of a standardised composite site fidelity index and its statistical distribution in order to obtain reliable population-level site fidelity comparisons. The arithmetic and harmonic means were used as mathematical structures in order to create different indexes by combining the most commonly used indicators for site fidelity such as Occurrence, Permanence and Periodicity. The index performance was then evaluated in simulated populations and one real population of Commerson’s dolphins (Cephalorhynchus commersonii (Lacépède 1804)). In the first case, the indexes were evaluated based on how they were affected by different probability values such as the occurrence of the individual within the study area (φ) and capture probability (p). As a precision measure for the comparison of the indexes, the Wald confidence interval (CI) and the mean square error were applied. Given that there was no previous data concerning the distribution parameters of this population, bootstrap CIs were applied for the study case. Results Eight alternative indexes were developed. The indexes with an arithmetic mean structure, in general, had a consistently inferior performance than those with a harmonic mean structure. The index IH4, in particular, achieved the best results in all of the scenarios and in the study case. Additionally, this index presented a normal distribution. As such, it was proposed as a standardised measure for site fidelity (Standardised Site Fidelity Index—SSFI). Discussion The SSFI is the first standardised metric that quantifies site fidelity at a populational level. It is an estimator that varies between zero and one and works in situations where detection is not perfect and effort can be constant or not. Moreover, it has an associated CI that allows users to make comparisons.