Demographics of the Disappearing Bottlenose Dolphin in Argentina: A Common Species on Its Way Out?

Abstract

Populations of the once common bottlenose dolphin (Tursiops truncatus) in Argentina have precipitously declined throughout the country in the past decades. Unfortunately, local declines of common species are easily overlooked when establishing priorities for conservation. In this study, demographics of what may well be the last remaining resident population in the country were assessed using mark—recapture analysis (Pollock’s Robust Design) of a photo-identification dataset collected during 2006–2011 in Bahía San Antonio (Patagonia, Argentina). Total abundance, corrected for unmarked individuals, ranged from 40 (95%CI: 16.1–98.8) to 83 (95%CI = 45.8–151.8) individuals and showed a decrease over the years. Adult survival rates varied between 0.97 (± 0.037 SE) and 0.99 (± 0.010 SE). Average calving interval equalled 3.5 ± 1.03 years, with 3.5 births/year in the entire population and a minimum annual birth rate of 4.2%. However, data suggest that calves may have been born and lost before being documented, underestimating birth rate, calf mortality, and possibly the number of reproductive females. Either way, the recruitment rate of calves appears to be insufficient to support the size of the population. This population is relatively small and declining. Considering the disappearance of populations north and south of the study area, an incessant decline will have severe consequences for the continuous existence of this species in Argentina, indicating an urgent need for serious conservation efforts. This study provides insight into how the failure to recognize local population declines can threaten the national (and eventually the international) status of a common species like the bottlenose dolphin.

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

“…Furthermore, in fissionfusion societies such as that of the bottlenose dolphin, one reason groups are believed to increase in size is to reduce predation risk (e.g., Heithaus & Dill, 2002). Therefore, the large amount of resting behaviour and the small median group size observed during resting behaviour seems to corroborate the low predation risk in the study area, reported previously by Vermeulen & Bräger (2015). This hypothesis seems further supported by the large number of dolphin groups with calves observed in the area.…”

“…It might also explain the relatively high degree of residency of the population within this area (Vermeulen & Cammareri, 2009). Nonetheless, as this population also recently has been reported as declining (Vermeulen & Bräger, 2015), further detailed studies on foraging behaviour, targeted prey species, and carrying capacity are essential. In terms of conservation management, the presented information seems crucial in the evaluation of the recently commenced tourism activities as any potential of area avoidance might lead to a sudden decrease in the population's carrying capacity (Lusseau, 2005) with potentially devastating effects.…”

“…One of the last remaining resident populations of the country is suggested to reside in BSA (Río Negro province; Vermeulen & Cammareri, 2009). Research conducted in this area described this population as small, essentially closed, declining (Vermeulen & Bräger, 2015), and highly resident to the study area, indicating this bay as the core region within the larger home range of this population (Vermeulen & Cammareri, 2009). This study aims to provide a better understanding of the activity patterns of this vulnerable population of bottlenose dolphins.…”

A Robust Design Capture-Recapture Analysis of Abundance, Survival and Temporary Emigration of Three Odontocete Species in the Gulf of Corinth, Greece

“…The abundance and survival estimates produced in this study can be used for the evaluation of these populations’ extinction risks trough Population Viability Analysis [24, 94, 95, 96, 97] and, ideally, for conservation status assessment following IUCN criteria for regional populations [24, 98]. A challenge is to incorporate the effect of hybridization on demographic rates [87].…”

First estimate of common bottlenose dolphin (Tursiops truncatus) (Cetacea, Delphinidae) abundance off Uruguayan Atlantic coast

“…Bearzi et al, 2005; and in the Adriatic Sea (Bearzi et al, 2004). This reinforces that the decrease in sighting frequency of dolphins in the estuarine coast of Uruguay, as has occurred in the estuarine Argentinean coast, could be related to overfishing and/or habitat degradation (Bastida et al, 2007;Coscarella et al, 2012;Vermeulen and Bräger, 2015).…”