Pontoporia Blainvillei Research Articles

Stitcher: A Surface Reconstruction Tool for Highly Gyrified Brains.

Brain reconstruction, specially of the cerebral cortex, is a challenging task and even more so when it comes to highly gyrified brained animals. Here, we present Stitcher, a novel tool capable of generating such surfaces utilizing MRI data and manual segmentation. Stitcher makes a triangulation between consecutive brain slice segmentations by recursively adding edges that minimize the total length and simultaneously avoid self-intersection. We applied this new method to build the cortical surfaces of two dolphins: Guiana dolphin (Sotalia guianensis), Franciscana dolphin (Pontoporia blainvillei); and one pinniped: Steller sea lion (Eumetopias jubatus). Specifically in the case of P. blainvillei, two reconstructions at two different resolutions were made. Additionally, we also performed reconstructions for sub and non-cortical structures of Guiana dolphin. All our cortical mesh results show remarkable resemblance with the real anatomy of the brains, except P. blainvillei with low-resolution data. Sub and non-cortical meshes were also properly reconstructed and the spatial positioning of structures was preserved with respect to S. guianensis cerebral cortex. In a comparative perspective between methods, Stitcher presents compatible results for volumetric measurements when contrasted with other anatomical standard tools. In this way, Stitcher seems to be a viable pipeline for new neuroanatomical analysis, enhancing visualization and descriptions of non-primates species, and broadening the scope of compared neuroanatomy.

Detailed Comparison of Acoustic Signals from Rehabilitated and Wild Franciscanas (Pontoporia blainvillei) Dolphins.

The franciscana dolphin is a small, vulnerable species often caught in artisanal gillnets. This study aims to provide a comprehensive assessment of their acoustic capabilities by using advanced equipment to collect a large dataset of wideband, continuous recordings. We examined the detailed acoustic signals of franciscana dolphins, comparing the sounds from rehabilitated dolphins in captivity with those of wild dolphins near fishing nets. Significant differences in acoustic characteristics were found between neonates and older dolphins, with juvenile and wild dolphins showing similar features. For the first time, repetition patterns in click production were identified, highlighting the importance of understanding the context of these sounds in regards to feeding and communication. This study emphasizes the need for detecting neonates for species protection and suggests the potential for developing acoustic classifiers specific to different age groups. Our findings offer valuable insights for conservation efforts and the development of protection strategies for franciscana dolphins.

Plastic ingestion by odontocetes from the Western South Atlantic: A particular concern to a threatened species

The ingestion of debris by marine fauna is a growing threat to biodiversity. This study aimed to evaluate and characterize litter ingestion by odontocetes from the Western South Atlantic. Between 2018 and 2022, 154 stomachs from six species were collected from stranded individuals and incidental captures. Stomach contents were analyzed with the naked eye and items of anthropic origin found were counted and physically/chemically characterized. Generalized Linear Models were used to evaluate the influence of biological factors on the presence/absence of litter in stomachs, and for Pontoporia blainvillei only, the influence of these factors on the number of ingested items was also tested; additionally, a temporal analysis of ingestion was done for this species (1994–2022). A total of 156 items, mainly macro-sized plastics made of polypropylene, were found in 52 stomachs of four species: Tursiops spp. (FO% = 3.3%), Steno bredanensis (10.0%), Delphinus delphis (28.6%) and P. blainvillei (47.5%). The presence/absence of litter was explained only by species (χ2 = 28.29 and p < 0.001). For P. blainvillei, a threatened species in the region, the number of items was positively influenced by individual size (χ2 = 6.01 and p = 0.01) and sex (χ2 = 7.93 and p = 0.005). There was an increase in plastic ingestion by this species over the years (χ2 = 121.6 and p < 0.001) and it was estimated that 75% of P. blainvillei stomachs will contain plastic by 2040. The ingestion of litter by odontocetes from the Western South Atlantic was confirmed and the potential risks posed by this type of pollution were evidenced, especially since these species also face other anthropic pressures. These results further demonstrate the increasing threat of litter in the ocean and highlight the importance of circularity of plastics and proper waste management.

Disparity of turbinal bones in placental mammals.

Turbinals are key bony elements of the mammalian nasal cavity, involved in heat and moisture conservation as well as olfaction. While turbinals are well known in some groups, their diversity is poorly understood at the scale of placental mammals, which span 21 orders. Here, we investigated the turbinal bones and associated lamellae for one representative of each extant order of placental mammals. We segmented and isolated each independent turbinal and lamella and found an important diversity of variation in the number of turbinals, as well as their size, and shape. We found that the turbinal count varies widely, from zero in the La Plata dolphin, (Pontoporia blainvillei) to about 110 in the African bush elephant (Loxodonta africana). Multiple turbinal losses and additional gains took place along the phylogeny of placental mammals. Some changes are clearly attributed to ecological adaptation, while others are probably related to phylogenetic inertia. In addition, this work highlights the problem of turbinal nomenclature in some placental orders with numerous and highly complex turbinals, for which homologies are extremely difficult to resolve. Therefore, this work underscores the importance of developmental studies to better clarify turbinal homology and nomenclature and provides a standardized comparative framework for further research.

Bioaccumulation of trace elements in marine mammals: New data and transplacental transfer on threatened species

Coastal areas are affected by urban, industrial and agriculture pollutants runoff, wastewater and stormwater discharges, making this environment the final repository of chemical contaminants. These contaminants have the potential to spread out to the entire food chain, impacting marine life and the quality of their habitat. In this aspect, the concept of marine mammals as bioindicators provides an approach to the degree of contamination in the environment and to the identification and management of multiple sources of contaminants. The present study analyzed several elements like As, Ba, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, V and Zn in liver tissue from two dolphin species: Sotalia guianensis, a near-threatened species, and the vulnerable Pontoporia blainvillei. In the study, we also investigated if dolphins (population) recorded using the heaviest urban areas have higher concentrations of contaminants in their tissues. Dolphin samples (n = 40 S. guianensis; n = 97 P. blainvillei) were collected by daily monitoring carried out by Santos Basin Beach Monitoring Project (PMP-BS), from stranded individuals found in São Paulo state. The Spearman's rank correlation showed distinct correlations in the accumulation of trace elements by both species, indicating different sources of exposure to the elements studied or distinct biochemical processes between species. Interspecific and intraspecific variations were observed, possibly related to the individual distribution and feeding habits. Correlations were observed between age and concentrations of trace elements, positive for Cd, Hg and Mo. Finally, our findings indicate high levels of Cu, Zn, and concentrations of As, V and Hg in fetuses, in particular, an analysis was performed on a fetus found inside a stranded individual, indicating placental transfer as the first route of exposure for some elements.

Overlapping Areas Used for Artisanal Fishing and Populations of Franciscana Dolphin (Pontoporia blainvillei) in the Southwest Atlantic Ocean

This study identified the overlap between artisanal fishing areas and the Franciscana dolphin (Pontoporia blainvillei) in the Southwest Atlantic Ocean (SWAO), Brazil, to identify areas where the species was incidentally captured from the perception of artisanal fishers. Using a semistructured questionnaire, ethnographic interviews (n = 330) were carried out from 2012 to 2018 with fishers from ten communities in southeastern (ES and RJ) and southern (PR) Brazil. After the interviews, the fishers presented their fishing routes, locations and areas of incidental capture and occurrence of the Franciscana dolphin. Ninety-five fishers (29%) identified the species: 23 in northern ES, 1 in southern ES, 20 in northern RJ, and 51 in the PR. Among the 235 fishers who could not identify the species, approximately half worked in the distribution gaps. The areas of occurrence noted by the fishers coincided with those described in the “National Action Plan for the Conservation of the Toninha,” an official document from the Brazilian Government and scientific literature. The results indicate that the information provided by fishers is useful for understanding the distribution of the Franciscana dolphin and can be used in the development of management strategies to mitigate the incidental capture of the species.

Detection of phthalate esters and targeted metabolome analysis in Franciscana dolphin (Pontoporia blainvillei) blubber in the coast of Santa Catarina, southern Brazil

The concerning of plastic pollution in different ecosystems has been worsened by the widespread presence. Phthalate esters (PAEs), plasticizers found in everyday products, can migrate into the environment, especially into the oceans. Researches on their effects on cetaceans are still rare. Metabolomics helps assess perturbations induced by exposure to PAEs, which act as persistent endocrine disruptors. Four PAEs (dimethyl phthalate - DMP, diethyl phthalate - DEP, dibutyl phthalate - DBP, and di(2-ethylhexyl phthalate – DEHP) were analyzed, along with cholesterol and fatty acid profiles of P. blainvillei's blubber samples collected in southern Brazil. The study reveals pervasive contamination by PAEs - especially DEHP, present in all samples - with positive correlations between DEP content and animal size and weight, as well as between the DEHP amount and the C17:1 fatty acid. These findings will be relevant to conservation efforts aimed at this threatened species and overall marine ecosystems.

Mercury Concentrations in Two Populations of the most Endangered Dolphin (Pontoporia blainvillei) from the Southwestern Atlantic Ocean.

Mercury contamination has been aggravated by emerging environmental issues, such as climate change. Top predators present concerning Hg concentrations once this metal bioaccumulates and biomagnifies. This study evaluated total mercury (THg) concentrations in tissues of 43 franciscanas (Pontoporia blainvillei) from two populations: the Franciscana Management Area (FMA) IIb and FMA IIIa. Animals from FMA IIIa showed mean concentration 5-times and 2.5-times higher in the liver and kidney (4.73 ± 6.84 and 0.52 ± 0.51µg.g-1, w.w., respectively) than individuals from FMA IIb (0.89 ± 1.04 and 0.22 ± 0.15µg.g-1, w.w., respectively). This might be due to: (I) individuals sampled from FMA IIIa being larger and older, and/or (II) the area near FMA IIIa presents environmental features leading to higher THg availability. Coastal contamination can affect franciscanas' health and population maintenance at different levels depending on their life history and, therefore, it should be considered to guide specific conservation actions.

Interactions between Cetaceans (suborder Odontoceti) and Artisanal Fishing in Brazil: an ethnoecological approach

Studies based on the relationship between humans and the natural environment have been proven to be important tools for understanding the influence, knowledge, and perceptions associated with the web of interactions between humans, species and ecosystems. Here, we highlight the interactions between cetaceans and artisanal fishing. Thus, this study aimed to: a) compile studies that consider artisanal fishing and its interactions with small cetaceans in Brazil; b) understand research trends over the years; c) analyse the distribution of studies by country region; d) perform authorship and citation analyses; e) classify the interactions between cetaceans and artisanal fishing recorded by authors and f) identify dolphin species registered in the study. To achieve this, we reviewed the current status of national publications related to the interactions of cetaceans (suborder Odontoceti) with artisanal fishing in Brazil, focusing on ethnoecological studies. Seven databases were used to survey the studies. To classify the interactions, we adopted the categorization proposed by Freitas-Netto and adapted by Di Beneditto. Based on the data analysis, we registered 12 types of interactions, seven of which were grouped according to the descriptions proposed by Di Beneditto and five new categories were described based on the results of this study. The studies reported the interaction of 43.2% (n=16) of the 37 odontocete species reported to occur in Brazil, with emphasis on the species Sotalia guianensis, Tursiops truncatus, Pontoporia blainvillei, Inia geoffrensis and Sotalia fluviatilis. From our research it was possible to observe that ethnoecological studies allow us to answer important questions about the occurrence of species and aspects of fishing. Furthermore, we reinforce the importance of developing studies which focus on the knowledge of the existing relationships between cetaceans and traditional fishing methods, since studies on this topic can generate data that contribute to the establishment of mitigation strategies and the management of species and ecosystems.

PAHs in franciscana dolphins from the Southwestern Atlantic Ocean: Concentration and maternal transfer assessments

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds ubiquitous in the environment and known for their toxic, mutagenic, and carcinogenic effects. These compounds can bioaccumulate in the biota and be transferred through trophic webs. The franciscana dolphin (Pontoporia blainvillei), as top predators, can be an environmental sentinels. Thus, this study aimed to provide data about PAHs concentration in their hepatic tissue collected on the coast of Espírito Santo (Franciscana Management Area, FMA Ia), Rio de Janeiro (FMA IIa), and São Paulo states (FMA IIb), in Southeastern Brazil. PAHs were detected in 86 % of franciscana dolphins (n = 50). The highest ∑PAHsTotal median concentration was reported in FMA Ia followed by FMA IIb and FMA IIa (1055.6; 523.9, and 72.1 ng.g-1 lipid weight, respectively). Phenanthrene was detected in one fetus and two neonates, showing maternal transfer of PAHs in these dolphins. Evaluating PAHs with potential toxic effects is of utmost importance for the conservation of a threatened species.

Trophic ecology and small‐scale differentiation of ecological groups of franciscana dolphin, Pontoporia blainvillei, in southeastern Brazil, revealed by carbon and nitrogen stable isotopes

AbstractThe franciscana, Pontoporia blainvillei, is an endemic dolphin off the east coast of South America and is considered the most endangered cetacean in the western South Atlantic. In the present study, we analyzed the muscle tissue of 24 franciscana dolphins found on the coast of Espírito Santo (ES) between 2010 and 2019 to investigate trophic ecology using carbon and nitrogen stable isotope analysis. In addition, 127 prey were analyzed to identify the preferred prey. The most important prey species in the diet of the franciscana dolphins were Trichiurus lepturus, Chirocentrodon bleekerianus, and Pellona harroweri. The franciscana dolphins were grouped into three subareas according to where they were collected throughout the distribution: 1 (North), 2 (Center), and 3 (South). In subarea 1, the preferred prey were Stellifer spp., Isopisthus parvipinnis, and P. harroweri, while in subareas 2 and 3, the prey were similar, changing the order of preference among them (Stellifer spp., T. lepturus, and C. bleekerianus). Finally, we identify two possible ecological groups of franciscana dolphins on the coast of ES, influenced by different carbon sources. Our results improve our understanding of the franciscana dolphin's trophic ecology and habitat use, providing new information and guidelines for species conservation in the region.

Nature or Nurture: Is the Digestive System of the Pontoporia blainvillei Influenced or Determined by Its Diet?

The Franciscana (also known as the La Plata River Dolphin) is a small dolphin that lives in the coastal waters of Brazil, Uruguay, and Argentina. This species is considered the most endangered marine mammal in the western South Atlantic Ocean. Anatomic dissection of the digestive system of 19 animals of different ages, including 2 neonates, 12 juveniles, and 5 adults, was performed. Parameters related to length, breadth, weight, and diameter of the digestive viscera were considered in each case. Our results show that the Franciscana dolphin presents differential characteristics in relation to several parts of the digestive system, including, specifically, the tongue, the teeth, the stomach, and the small intestine. Thus, this paper add precious information to the actual knowledge of this vulnerable marine mammal species in order to improve conservation efforts.

Molecular Detection and Characterization of Mycoplasma spp. in Marine Mammals, Brazil.

Mycoplasma spp. are wall-less bacteria able to infect mammals and are classified as hemotropic (hemoplasma) and nonhemotropic. In aquatic mammals, hemoplasma have been reported in California sea lions (Zalophus californianus) and river dolphins (Inia spp.). We investigated Mycoplasma spp. in blood samples of West Indian manatees (Trichechus manatus), pinnipeds (5 species), and marine cetaceans (18 species) that stranded or were undergoing rehabilitation in Brazil during 2002-2022. We detected Mycoplasma in blood of 18/130 (14.8%) cetaceans and 3/18 (16.6%) pinnipeds. All tested manatees were PCR-negative for Mycoplasma. Our findings indicate that >2 different hemoplasma species are circulating in cetaceans. The sequences from pinnipeds were similar to previously described sequences. We also detected a nonhemotropic Mycoplasma in 2 Franciscana dolphins (Pontoporia blainvillei) that might be associated with microscopic lesions. Because certain hemoplasmas can cause disease and death in immunosuppressed mammals, the bacteria could have conservation implications for already endangered aquatic mammals.

What do small cetaceans tell us about trace elements pollution on the Argentinean coast? Franciscana dolphin as a biomonitor

Trace elements (TEs) constitute the oldest emerging pollutants globally, most occur from natural sources, but a few are derived from anthropogenic sources. Marine mammals are considered bioindicators of ecosystem contamination. The aims of this review is compile reports on essential and nonessential TEs occurrence in small cetaceans from Argentinean waters; and to review the existing information on the concentration of TEs in the Franciscana dolphin, a biomonitor species of the Argentine coastal marine ecosystem. We searched reports where levels of TEs were present in small cetaceans from and eight species were analysed: Pontoporia blainvillei, Tursiops truncatus gephyreus, Kogia breviceps, Delphinus delphis, Lagenorhynchus obscurus, Lagenodelphis hasei, Cephaloryhchus commersonii and Ziphius cavirostris. Essential TEs like Zn, Cu, Mn, Cr, Fe, Co, Ni, Mo, Se, As, Au, Ag, Sn, and nonessential TE as Pb, Cd, Hg, As was considered. The reports compiled in this article analysed kidney, liver, muscle and occasionally brain, skin, lung and spleen, covering a temporal range of 30 years, from 1982 to 2016. Of data analysis, we identify knowledge gaps, species of small cetaceans for which the concentration of trace metals is not yet known and areas on the Argentine coast where there are no reports that analyse them. The most recent information corresponds to the 2010 decade, and in those subsequent publications, the samples were taken at that time. This emphasizes the importance of reviewing this data, in order to compare old and new datasets, create contamination timelines and evaluate possible increases or decreases of contaminants in different study areas. The information recopilated will serve as valuable baselines to detect the future impact of increasing human, even natural, activities on marine ecosystems in the South Atlantic Ocean.

From narrow and overlapped to wide and segregated: The isotopic niche of a tropical cetacean community

Species in sympatry can coexist due to some degree of niche partitioning. Four cetacean species, Guiana (Sotalia guianensis), franciscana (Pontoporia blainvillei), Atlantic spotted (Stenella frontalis), and rough-toothed dolphins (Steno bredanensis), frequently occur in Ilha Grande Bay (RJ), with three of them presenting residence pattern. This tropical bay is considered a biodiversity hotspot and preserved by marine protected areas, though located in a highly developed region of the Southwestern Atlantic Ocean. To verify niche partitioning and segregation in these species and to explore the trophic structure of this cetacean community, their isotopic niches were investigated through carbon (δ13C) and nitrogen (δ15N) stable isotopes in the muscle of specimens stranded in the region between 2012 and 2022. The rough-toothed dolphin had the largest niche area and high segregation. On the other hand, there was a high niche overlap between the species that have site fidelity patterns in the bay. The Atlantic spotted dolphin had the highest values for almost all the Layman metrics, a large niche area, and trophic diversity; the Guiana dolphin explored a diverse variety of resources, and the franciscana dolphin presented the narrowest and most overlapped niche and the lowest niche diversification. This is the first study to access the trophic ecology of this cetacean community. Our results indicate that the region is an important foraging area for three of the studied species, with a high diversity and availability of resources that might enable the high niche overlap observed for resident species. The findings for the threatened and small franciscana population in this recently discovered habitat bring concern. Therefore, the area deserves conservation attention to prevent anthropogenic stressors from interfering in the relationship balance between these sympatric predators.

Trophic Chain Organochlorine Pesticide Contamination in a Highly Productive Upwelling Area in Southeastern Brazil.

Organochlorine pesticides (OCP) are legacy anthropogenic compounds known to persist for several years in the environment. The continuous use of some OCP, such as DDT, after restrictions in developing countries are cause of concern, due to their deleterious effects to marine life and humans. Studies assessing OCP contamination in coastal environments are still scarce in South America and there is a need to understand the impacts from trophic chain accumulation of these pollutants in marine life. In this study, we have assessed OCP levels in muscle and liver and estimated the biomagnification factor in several upwelling system trophic chain members, including fish, squid, and marine mammal from Southeastern Brazil. DDT degradation product DDE was the OCP detected in the highest concentrations in Franciscana dolphins (Pontoporia blainvillei), 86.4 ng·g-1 wet weight, and fish muscle and liver. In general, higher OCP levels were found in liver than in muscle, except for croaker. Biomagnification factors (BMF) of OCP in the top predator P. blainvillei and the carnivorous cutlass fish (Trichiurus lepturus) were on average between 0.2 and 1.8. Continued OCP monitoring in this region is warranted to better understand the distribution and fate of these compounds over time, with the goal to establish strategies for the conservation of local dolphin species and to assess human health risks from local coastal region populations.

Artisanal fishery with surface gillnets and megafauna strandings

Bycatch is an issue of worldwide relevance involving conflicts between conservation and fishery interests. In Brazil, this conflict has been highlighted in relation to the regulation of small-scale fishery with surface gillnets. To promote management and transformation of this conflict, we analyzed the relationship between catch unloadings from small-scale fishing with surface gillnets and strandings of marine megafauna. We used fishery monitoring data and beach monitoring data in São Paulo between 2015 and 2021, relating to Chelonia mydas, Caretta caretta, Lepidochelys olivacea, Pontoporia blainvillei and Sotalia guianensis. The analyses included (i) overview of catches unloadings from small-scale fishing with surface gillnets and strandings that resulted in the death of each of these species over the course of the year; (ii) correlation tests between those variables for the northern, central, and southern regions; and (iii) performing regression analyses for municipalities within these regions, exhibiting statistically significant positive correlations. The fisheries harvest period was found not to overlap with the stranding distribution. In correlation tests, only strandings of C. mydas in the northern and southern regions, S. guianensis in the southern region and P. blainvillei in the central region showed relationships with fishing landings. The regression analysis was significant for C. mydas and S. guianensis. At the municipal level, the results were statistically significant for C. mydas in São Sebastião, Ubatuba, Ilha Comprida and Cananéia and for S. guianensis in Cananéia. However, the regression explained a small part of the mortality and other impact factors were pointed out. Non-prohibitive management measures, participatory studies, and direct methods for evaluating the interaction between fisheries and megafauna associated with environmental factors should be implemented, along with analyses on other impacts on megafauna.

Ecological traits of the franciscana dolphin (Pontoporia blainvillei) from the Late Pleistocene to the present days based on stable isotope analysis

AbstractLate Pleistocene fossils from southern Brazil provide a unique opportunity to study the diet and habitat use of the extant franciscana dolphin (Pontoporia blainvillei) prior to human influence. Here, we subject 19 fossil and 21 contemporary specimens to stable carbon and oxygen isotope analysis (after first ruling out diagenesis via Fourier transform infrared spectroscopy). The two groups differ in their isotopic composition (PERMANOVA, p &lt; .01), with fossils yielding more disparate δ13C values and recent samples more disparate δ18O values. Their isotopic niches show an overlap of ~20%, with that of the fossils being slightly wider (SEAc = 2.25‰2 versus 1.84‰2). We attribute these differences to impoverished modern fish communities and temporal changes in freshwater influx.

Molecular Detection of Pathogenic Leptospira sp. in Cetaceans from the Brazilian Coast

Leptospirosis is a zoonosis with ubiquitous distribution caused by spirochetes belonging to the genus Leptospira sp., endemic mainly in tropical and subtropical regions of the world and capable of infecting domestic animals, free-living animals, and humans. Although well documented in terrestrial animals and humans, little information is available on its distribution and impact on marine animals. There are few studies assessing cetaceans’ health status, and even scarcer are those focused on leptospirosis research. In this context, considering the One Health approach, the present study aimed to investigate the occurrence of pathogenic Leptospira sp. in cetaceans on the Brazilian coast. Kidneys of 142 cetaceans belonging to 19 species were collected. DNA was extracted, and the diagnosis was performed by LipL32-polymerase chain reaction. Genetic characterization was conducted based on secY gene sequencing. Pathogenic Leptospira sp. DNA was detected in 14.8% (21/142) of the tested cetaceans, with coastal species presenting a significantly higher frequency (p-value = 0.03) of infected individuals (25%, 17/68) than oceanic species (7.5%, 4/53). It was possible to amplify and sequence three strains (one for Sotalia guianensis, one for Stenella clymene, and one for Pontoporia blainvillei), all of them identified as Leptospira interrogans, with high similarity with sequences from Icterohaemorrhagiae serogroup. Phylogenetic analysis revealed sequences from the present study grouped in species-specific unique clusters but very close to pinnipeds in the same area, evidencing the presence of two distinct haplotypes circulating on marine mammals in the region. We could demonstrate that cetaceans can act as carriers of pathogenic leptospires. Moreover, the proximity with anthropogenic areas could play an important role in leptospirosis’ dynamics of transmission in a One Health context.

Biology and conservation of the franciscana (Pontoporia blainvillei) in the north of Rio de Janeiro State, Brazil

This paper describes the interactions of the franciscana (Pontoporia blainvillei) with fisheries in the north of Rio de Janeiro State (210 18’S-220 25’S) and presents new information on its biology. A total of 181 dolphins were caught in gillnet fisheries in northern Rio de Janeiro from 1986-1999. The annual catch per unit effort (CPUE) values varied from 0.2-1.8 dolphins per gillnet fishing effort. Incidental captures were recorded throughout the year, usually less than 10 n.miles from shore, in depths less than 30m and in surface-set gillnets. There was no difference in the proportion of sexes (1 male:1.1 females). Males ranged from 66-130.0cm and 0-5 years and females from 74-147.5cm and 0-9 years. The predicted asymptotic length (using the Gompertz model) was 121.9cm for males and 145.6cm for females. Calving occurs throughout the year, with no seasonal pattern. Females attain sexual maturity at 3 years and 130.0cm in length and males at 2 years and 115.0cm. Individuals up to the age of three years represented 74% of the dolphins captured. Franciscana preferentially feed on the teleosts Stellifer sp., Anchoa filifera, Pellona harroweri and Isopisthus parvipinnis, measuring up to 10cm of length, and on the cephalopods Loligo sanpaulensis and L. plei. No internal parasites were observed. The barnacle Xenobalanus globicipitis was recorded on only one individual. Sightings were recorded in all seasons and 90% of them were obtained up to 5 n.miles from shore, in waters up to 15m deep. Around 70% of groups sighted consisted of up to five dolphins. Estimates of the population size and continuous gillnet fleet monitoring are required to conserve franciscana in the northern limit of its distribution range. The differences in the somatic, reproductive and genetic patterns of franciscana represent important aspects that may be used as evidence to best define their stocks. These variations may reflect the reduction of gene flow between populations, the allocation of resources between growth and reproduction and/or the influence of environmental features, such as water temperature and food availability.