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Guiana Dolphin Population Viability in a South Atlantic Estuary

Coastal cetaceans are constantly exposed to bycatch, boat collisions, chemical and noise pollution, habitat loss and tourism activities. Changes in the habitat quality and coastal waters during the past decades are significant and it is believed that many wild species have already been affected by human activities.

Information on abundance, density and population dynamics are fundamental for establishing management strategies for species conservation. The distribution and identification of areas in which biological and socially relevant behavior (eg. feeding, breeding, resting) are associated, are important information in the investigation of environmental issues and conservation.

Guiana dolphin (Sotalia guianensis) is a small coastal cetacean found along the south-western Atlantic Ocean, classified as Near Threatened in The IUCN Red List of Threatened Species and as Vulnerable in the Red Book of Endangered Brazilian Fauna. The species is in constant proximity to human activities being susceptible to a wide variety of threats. Many variables are influenced by environmental changes (eg. survival, reproduction, birth), and consequently influence the population trends and persistence over time. All these factors and variables act both, independently and combined, leading to different responses of the population.

The main threats identified in the Cananéia estuary, are bycatch in fishing nets, vessel traffic and tourism. Listed as an UNESCO World Heritage since 1999, the Cananéia Estuarine-Lagoon Complex, São Paulo state, Brazil, is located within the natural boundary between two state conservation units, Ilha do Cardoso State Park and Lagamar de Cananéia State Park and is included in the Federal Environmental Protection Area of ​​Cananéia-Iguape-Peruíbe and in the Wildlife Conservation Zone. Due to its great biological richness and well preserved status it is one of the most important coastal ecosystems in the country.

This study gathered historical, ecological and demographic information about Guiana dolphin throughout its distribution and performed a population viability analysis for different scenarios of anthropogenic activities in the Cananéia estuary. Estimates of abundance, density and distribution in the estuary were obtained using the distance sampling method and linear transects, with approximately 1400 km in effort. After that, were modeled scenarios in which specific parameters variations (mortality, environmental carrying capacity, environmental variation in reproduction and catastrophe) were used to assess population trends under different threats (fishery, tourism and vessel traffic) on a Population Viability Analysis (PVA). 

PVA is a way to predict the trends and probability of persistence or extinction of a species or population over time, incorporating demographic, ecological and environmental data of real populations in computer simulations of stochastic and deterministic models. The analyses showed that even small variations in population size, mortality, carrying capacity and disasters can strongly influence the persistence of small populations and the population could become extinct in less than two generations of the species in response to these variations. 

Although the Cananéia estuary is a well preserved environment and sustain a viable population of the species, the increase in anthropogenic activities in the estuary may lead to changes in population dynamics and habitat quality, compromising their persistence over time. 

This research was part of a PhD in Applied Ecology by the University of São Paulo, and counted on the support of the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Instituto de Oceanografia (IOUSP) and Cetacean Society International (CSI).

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