Diurnal and Seasonal Variation in the Behaviour of Bottlenose Dolphins (Tursiops truncatus) in Bahía San Antonio, Patagonia, Argentina

Abstract

Diurnal and seasonal patterns in the behaviour of a small population of bottlenose dolphins were assessed in Bahía San Antonio (BSA), Patagonia, Argentina, between 2006 and 2011. Results indicated that dolphins used the study area mainly to rest, travel, and forage, with a marked diurnal and seasonal pattern in their activity. During the early morning, most dolphin groups were resting, while towards the afternoon and evening, surface feeding and social activities peaked. During winter, social activities and surface feeding increased notably; during summer, diving behaviour reached its peak, presumably associated with a tail-out/peduncledive foraging strategy. The observed seasonal variation in foraging strategies is hypothesised to be related to the seasonal behavioural changes of prey species in the area that are linked to spawning. The variation in group size further appears to reflect the regulation of feeding competition while reconfirming the low predation risk within the study area. Results of this study indicate the behavioural and social flexibility of bottlenose dolphins in BSA and suggest a link to the seasonal variations in prey availability. Considering the general bottlenose dolphin population declines in Argentina presumably related to prey depletion, it could be argued that the temporal occurrence of spawning shoals and a general low presence of other top predators directly and indirectly make this a favourable area for this population. Additional information is required to more comprehensively address this hypothesis. The information presented herein serves as vital baseline data for future conservation management protocols.

Genetic divergence between two phenotypically distinct bottlenose dolphin ecotypes suggests separate evolutionary trajectories

“…Sighting data from the literature indicates that coastal bottlenose dolphins are restricted to shallow waters of the southern coast of the continent (above 25–27°S), while the offshore ecotype preferentially inhabits deeper waters albeit some incursions to coastal areas can occur occasionally in the north limit of the distribution of the coastal ecotype. Despite opportunity for gene flow in this possible “contact zones” our results suggest negligible interbreeding between ecotypes, even in an area where dolphins of both ecotypes were observed to associate (Vermeulen & Cammareri, ). Based on our findings, which seem to be in agreement with the morphological differentiation described by Costa et al.…”

“…This is surprising given the absence of geographical barriers to gene flow in the broad geographical sampling area examined in the present study, which encompasses zones with high potential for gene flow between the ecotypes (i.e., zones of sympatry or where offshore ecotypes are often seen close to the shore). In Bahía San Antonio, for example, Vermeulen and Cammareri () reported the presence of three morphologically distinct individuals that were observed on a regular basis interacting together with individuals of the small coastal dolphin population of this area. Analyses of both molecular marker types clustered their genetic profile with the offshore ecotype, indicating they are likely migrants from the offshore population.…”

“…With the exception of three additional samples collected from dolphins regularly sighted in BSA that are morphologically distinct from their conspecifics, and resemble those of the putative offshore ecotype (Bastida, Rodríguez, Secchi, & da Silva, ; Vermeulen & Cammareri, – see Figure c), samples from coastal bottlenose dolphins ( n = 124) are the same used in a recent study that investigated the fine‐scale genetic structuring of these dolphins in the SWA (Fruet et al., ). In brief, 120 biopsies were collected between 2004 and 2012 during small boat‐based surveys conducted in coastal, shallow waters (<2 km from shore, <10 m deep) of southern Brazil, Uruguay, and Argentina.…”

Association patterns of bottlenose dolphins (Tursiops truncatus) in Bahía San Antonio, Argentina

“…This population also shows a marked seasonal pattern in grouping behavior with significantly larger groups observed in winter ( = 7) and the smaller groups in summer ( = 3; Vermeulen et al . ). The authors suggested this variation was caused by a seasonal variation in food availability, and regulation of feeding competition; i.e ., in winter prey seems to be abundant and dolphins are often engaged in cooperative surface feeding activities (in groups of on average 27 individuals, Vermeulen et al .…”

“…; Vermeulen and Bräger ; Vermeulen et al . , ). It is a small (approximately 83 individuals) and isolated population (Vermeulen and Bräger ), showing high levels of residency and site fidelity to the area of Bahía San Antonio (Vermeulen et al .…”