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Due to their worldwide distribution and occupancy of different types of environments, bottlenose dolphins display considerable morphological variation. Despite limited understanding about the taxonomic identity of such forms and connectivity among them at global scale, coastal (or inshore) and offshore (or oceanic) ecotypes have been widely recognized in several ocean regions. In the Southwest Atlantic Ocean (SWA), however, there are scarce records of bottlenose dolphins differing in external morphology according to habitat preferences that resemble the coastal‐offshore pattern observed elsewhere. The main aim of this study was to analyze the genetic variability, and test for population structure between coastal (n = 127) and offshore (n = 45) bottlenose dolphins sampled in the SWA to assess whether their external morphological distinction is consistent with genetic differentiation. We used a combination of mtDNA control region sequences and microsatellite genotypes to infer population structure and levels of genetic diversity. Our results from both molecular marker types were congruent and revealed strong levels of structuring (microsatellites F ST = 0.385, p < .001; mtDNA F ST =  0.183, p < .001; ΦST = 0.385, p < .001) and much lower genetic diversity in the coastal than the offshore ecotype, supporting patterns found in previous studies elsewhere. Despite the opportunity for gene flow in potential “contact zones”, we found minimal current and historical connectivity between ecotypes, suggesting they are following discrete evolutionary trajectories. Based on our molecular findings, which seem to be consistent with morphological differentiations recently described for bottlenose dolphins in our study area, we recommend recognizing the offshore bottlenose dolphin ecotype as an additional Evolutionarily Significant Unit (ESU) in the SWA. Implications of these results for the conservation of bottlenose dolphins in SWA are also discussed.

The study reviews the information available on the distribution patterns of bottlenose dolphins within the SWAO (04oN-56oS, 25oW-67oW) including the northern portion of Brazil, covering the period from 1894 to 2011.

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The franciscana dolphin (Pontoporia blainvillei) is the most threatened small cetacean in the southwestern Atlantic Ocean. Its incidental capture in the Uruguayan fisheries of the Atlantic oceanic coast (AOC) has been recorded since 1940 and was systematically studied from 1974 to 1994, providing the most recent by-catch per unit of effort estimate (BPUE) for the AOC region (0.0064 franciscanas per 1000m net per fishing set). The lack of new by-catch data during the past 12 years has led to a data gap in by-catch estimates for the species in Uruguay. The current study was developed in two separate stages, a first stage (July 2004 -December 2005 designed to identify fisheries that interact with franciscana, and a second stage (2006), designed to determine new BPUE and franciscana mortality estimates for the selected fisheries. During the first stage, 13 artisanal fisheries of the Uruguayan coast were visited monthly, while in the second stage five fisheries (including the Rio de la Plata estuary and the AOC) were selected for monitoring. During 2006, 26 fishermen recorded all the information related to each fishing event, allowing the estimation of fishing effort calculated in linear units multiplied by hour (FE L ). We also estimated a fishing set (FE S ) based by-catch rate which allowed the comparison with previously reported results. For 2006, the BPUE L (based on FE L ) was estimated at 0.0020 franciscanas per 1000m net per hour and the BPUE S at 0.0286 franciscanas per 1000m net per fishing set. The BPUE L was extrapolated to the surveyed fishing fleets during 2006, resulting in a mortality estimate of 289 (95% CI: 266-350) franciscanas. Based on the fishing dynamics reported herein, we consider the BPUE L the most accurate estimate of by-catch for the Uruguayan coast. This research updates the values of BPUE in the AOC after a 12-year information gap and includes the first by-catch evaluation in the Uruguayan estuarine coast. We highly recommend an abundance estimation of the species to complement the information reported herein in order to know the current status of franciscana dolphin population in Uruguay.RESUMEN: El delfín franciscana (Pontoporia blainvillei) es el pequeño cetáceo más amenazado de Atlántico Sudoccidental. La captura incidental de franciscanas en las pesquerías uruguayas de la costa del Océano Atlántico (AOC) ha sido registrada desde 1940 y relevada sistemáticamente entre 1974 y 1994; brindando el último valor de Captura Por Unidad de Esfuerzo (BPUE) en la AOC uruguaya (0,0064 franciscanas por1000m de red por lance). La ausencia de nuevos valores de BPUE durante 12 años produjo una carencia de datos sobre la captura incidental de la especie en Uruguay. El presente estudio fue realizado en dos períodos, el primero (Julio 2004-Diciembre 2005) con el objetivo de identificar las pesquerías que interactuaban con la franciscana, y el segundo período (año 2006) para determinar la BPUE y mortalidad de la franciscana en las pesquerías seleccionadas. En el primer período se visitaron mensualmente ...