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Estimation of visibility bias is critical to accurately compute abundance of wild populations. The franciscana, Pontoporia blainvillei, is considered the most threatened small cetacean in the southwestern Atlantic Ocean. Aerial surveys are considered the most effective method to estimate abundance of this species, but many existing estimates have been considered unreliable because they lack proper estimation of correction factors for visibility bias. In this study, helicopter surveys were conducted to determine surfacing-diving intervals of franciscanas and to estimate availability for aerial platforms. Fifteen hours were flown and 101 groups of 1 to 7 franciscanas were monitored, resulting in a sample of 248 surface-dive cycles. The mean surfacing interval and diving interval times were 16.10 seconds (SE = 9.74) and 39.77 seconds (SE = 29.06), respectively. Availability was estimated at 0.39 (SE = 0.01), a value 16-46% greater than estimates computed from diving parameters obtained from boats or from land. Generalized mixed-effects models were used to investigate the influence of biological and environmental predictors on the proportion of time franciscana groups are visually available to be seen from an aerial platform. These models revealed that group size was the main factor influencing the proportion at surface. The use of negatively biased estimates of availability results in overestimation of abundance, leads to overly optimistic assessments of extinction probabilities and to potentially ineffective management actions. This study demonstrates that estimates of availability must be computed from suitable platforms to ensure proper conservation decisions are implemented to protect threatened species such as the franciscana.

Due to anthropogenic factors, the franciscana dolphin, Pontoporia blainvillei, is the most threatened small cetacean on the Atlantic coast of South America. Four Franciscana Management Areas have been proposed: Espiritu Santo to Rio de Janeiro (FMA I), São Paulo to Santa Catarina (FMA II), Rio Grande do Sul to Uruguay (FMA III), and Argentina (FMA IV). Further genetic studies distinguished additional populations within these FMAs. We analyzed the population structure, phylogeography, and demographic history in the southernmost portion of the species range. From the analysis of mitochondrial DNA control region sequences, 5 novel haplotypes were found, totalizing 60 haplotypes for the entire distribution range. The haplotype network did not show an apparent phylogeographical signal for the southern FMAs. Two populations were identified: Monte Hermoso (MH) and Necochea (NC)+Claromecó (CL)+Río Negro (RN). The low levels of genetic variability, the relative constant size over time, and the low levels of gene flow may indicate that MH has been colonized by a few maternal lineages and became isolated from geographically close populations. The apparent increase in NC+CL+RN size would be consistent with the higher genetic variability found, since genetic diversity is generally higher in older and expanding populations. Additionally, RN may have experienced a recent split from CL and NC; current high levels of gene flow may be occurring between the latter ones. FMA IV would comprise four franciscana dolphin populations: Samborombón West+Samborombón South, Cabo San Antonio+Buenos Aires East, NC+CL+Buenos Aires Southwest+RN and MH. Results achieved in this study need to be taken into account in order to ensure the long-term survival of the species.

Line transect aerial surveys are widely used for estimating abundance of biological populations, including threatened species. However, estimates obtained with data collected from aircraft are often underestimated because of visibility bias and bias in estimating group sizes from a fast-moving platform. An assessment of multiple sources of bias in aerial surveys were carried out in Brazilian coastal waters by experiments on multiple survey platforms (i.e., boat, airplane and helicopter). These studies focused on evaluating visibility bias (perception and availability bias) and potential differences in the estimation of group sizes from different types of platforms used in franciscana ( Pontoporia blainvillei ) abundance surveys. The ultimate goal was to develop correction factors to improve accuracy of estimates of density and population size for this threatened dolphin. Estimates of density and group sizes computed from boats were assumed to be unbiased and were compared to estimates of these quantities obtained from an airplane in the same area and period. In addition, helicopter surveys were conducted in two areas where water turbidity differed (clear vs. murky waters) to determine surfacing-diving intervals of franciscana groups and to estimate availability for aerial platforms. Abundance computed from the aerial survey data underestimated the true abundance by about 4-5 times, with ~70% of the total bias resulting from visibility bias (~80% from availability bias and ~20% from perception bias) and ~30% from bias in estimates of group size. The use of multiple survey platforms in contrasting habitats provided the opportunity to compute correction factors that can be used to refine range wide abundance estimates of the threatened franciscana given certain assumptions are met. Visibility bias and group size bias were substantial and clearly indicate the importance for accounting for such correction factors to produce unequivocal population assessment based on aerial survey data.

Understanding diet variation is a major concern when developing conservation guidelines for threatened species, especially for marine predators whose prey availability can be reduced by commercial fisheries. Diet can vary in geographically structured populations due to variation in prey availability and within a location due to the effects of season, sex, age, and individual. However, these sources of variation are seldom considered together in dietary studies. We analyzed diet variation at the geographical and intrapopulation levels in the franciscana dolphin (Pontoporia blainvillei) by analyzing samples of stomach contents from individuals incidentally caught by artisanal fisheries. We investigated the geographical (Northern, Central, and Southern regions of the São Paulo State coast, Brazil) and intrapopulation effects of season, sex, and age. We used the leave-one-out cross-validation method to test for significance of the proportional similarity index, which measures the overlap between diet compositions. We found that diet varied across different levels, from the geographical to the individual level, including the effects of season, sex, and age. Diet variation as a function of age suggests an ontogenetic diet shift. Our findings indicate that ecological processes within local stocks should inform management at the local geographic scale. Evidence for ecological differences between franciscana stocks is of great significance for the conservation of this threatened species.

In this study we describe how franciscana and Guiana dolphin habitat use is influenced by tidal cycles and seasonality in Babitonga Bay. The franciscanas use a greater area in winter and a smaller area in summer, but the extent of the area used did not vary with the tide. Guiana dolphins did not change the extent of the area used within seasons or tides. Franciscanas remained closer to the mouth of the bay and the islands during ebb tide, moving to the inner bay areas and closer to the mainland coast during flood tide. Guiana dolphin used areas closer to the mainland coast during the flood tide. Guiana dolphin patterns of movement do not seem to be related to the tidal current. Franciscanas used sandier areas while Guiana dolphins preferred muddy areas, with some seasonal variation. We suggest that these dolphins modify their distributions based on habitat accessibility and prey availability. This study enhances our knowledge of critical habitat characteristics for franciscana and Guiana dolphins, and these factors should be considered when planning local human activities targeting species conservation.

The franciscana dolphin (Pontoporia blainvillei) is a small coastal dolphin endemic to the south-western Atlantic Ocean. Incidental captures in fishing gillnets is possibly the greatest conservation concern for this species, and occurs within most of its geographical distribution. The aim of this paper is to determine the biological parameters of franciscana dolphin by-caught from artisanal coastal fisheries of the southern Buenos Aires province, Argentina. Between 2003 and 2009, carcasses of 54 incidentally captured franciscanas were collected. The age, sexual and physical maturity and body condition of each specimen was determined. The sex-ratio of the by-caught dolphins did not differ from parity and, consistent with other areas, juveniles younger than 4 yr old were captured in higher proportion (69%). In addition, 74% of the entangled animals were sexually immature and 85% physically immature. Sexually immature dolphins were predominant in the spring, a period which coincides with the breeding season. An assessment of the body condition of captured franciscanas suggests that entanglements were not associated with a disease or physiological disorder. The results presented here are important to assess the impact of artisanal fisheries on the population of franciscana dolphins in the southernmost area of its distribution.

Research on the feeding habits of Franciscana dolphins (Pontoporia blainvillei) in waters along the Uruguayan coast was carried out using stomach contents from 41 individuals that were incidentally entangled in artisanal fishing nets or were stranded on the beach. A total of nine prey species were identified: eight teleosts and one squid. Teleosts were identified in 99.8% of the 37 stomach samples, corresponding to a total of 342 individuals. The striped weakfish (Cynoscion guatucupa) was the most important teleost by index of relative importance (IRI) (n = 127; IRI = 49.4%), followed by the toadfish (Porichthys porosissimus) (n = 90; IRI = 26.6%) and the whitemouth croaker (Micropogonias furnieri) (n = 66; IRI = 17.3%); whereas the remaining fish species represented less than 6.5% IRI. From eight species of fish found in stomach contents, four of them (striped weakfish, toadfish, whitemouth croaker, and Argentine croaker [Umbrina canossai]) actively produce sound. Fish, particularly those emitting sound, were the most important food content, representing 97.4% IRI. The Levin's index of niche breadth shows a specialist feeding strategy, and data indicated that the Franciscana chooses soniferous prey along the Uruguayan coast. Therefore, we suggest that Franciscana dolphins find their prey in the low visibility waters of the Rio de la Plata estuary and the murky waters of the Uruguayan ocean coast through passive listening. However, this behavior may also lead Franciscana dolphins to be attracted to artisanal fishing nets because of the sounds produced by the fish caught in nets, which puts them in danger of becoming entangled.

Evaluating population structure in the marine environment is a challenging task when the species of interest is continuously distributed, and yet the use of population or stock structure is a crucial component of management and conservation strategies. The franciscana dolphin (Pontoporia blainvillei), a rare endangered coastal cetacean, suffers high levels of by-catch all along its distribution range in the Western South Atlantic, and questions have been raised about boundaries or divisions for population management. Here we apply genetic tools to better understand population structure and migration, sex-biased dispersal, and to assess potential genetic and demographic impacts of by-catch. Our analyses, based on mtDNA control region sequences, reveal significant genetic division at the regional level and fine-scale structure within our study area. These results suggest that the population in northern Buenos Aires is the most isolated population in Argentina. We found no significant departure from an equal sex ratio among the by-caught animals. A few cases of multiple entanglements appeared to be mother-calf pairs based on field observations and individuals sharing the same mtDNA control region lineage. The distribution of haplotype frequencies observed could imply that some maternal lineages are more prone to be subject to higher rates of by-catch, although biopsy sampling is necessary to fully evaluate whether maternal lineage distributions are the same for biopsy sampled and by-caught animals. A genetic indication of population size disequilibrium was detected for all populations in Argentina, which is consistent with available rates of by-catch and abundance estimates. Collectively, our findings support the current scheme of larger recognized Franciscana Management Areas (FMA), but argue for a finer-scale subdivision within Northern Buenos Aires region (FMA IV). Finally, an integrated approach to promote conservation of this endangered small cetacean has to involve identification of genetic and demographic threats, a more sustainable fishery strategy to reduce by-catch, and designation of protected areas that are supported by underlying population structure for franciscana dolphins.

Lactation is a crucial stage for mammals. It is a defining characteristic of their reproductive cycle that involves a substantial investment of energy and nutrients by the mother (Oftedal, 1984). Stranded (alive and dead fresh) and entangled franciscana dolphin calves were collected in cooperation with the Fundacion Mundo Marino Rehabilitation Centre and local, artisanal fishermen. Calving chronology and lactation period were determined using the date of collection of each specimen. The results indicate a short period of exclusive milk intake. Based on the elapsed time between the first record of neonates and the first hard remains in stomach contents, this phase of lactation may last around 40 d during which calves more than double (ca. 2.2-times birth weight) their body mass and reach ca. 30% of the mother's mass. During the next phase of approximately 5 mo, the calves complement milk intake with solid food, indicating that weaning may be gradual.