Summary: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.Keywords: tide cycles; survey method; franciscana dolphin; Guiana dolphin; critical habitat; Babitonga Bay; SW Atlantic Ocean. Influencia de las mareas y las estaciones en el uso de hábitat de delfines en un estuario del sur de BrasilResumen: En este estudio describimos como el uso del hábitat del delfín franciscana y delfín costero es influenciado por los ciclos de mareas y las estaciones en la bahía Babitonga. Las franciscanas utilizan áreas mayores en invierno y menores en verano, pero el tamaño del área utilizada no varió con las mareas. El área de uso del delfín costero no varió entre estaciones ni con las mareas. Las franciscanas permanecieron más próximas a la boca de la bahía e islas durante la marea baja, moviéndose hacia áreas más internas cercanas al margen del continente durante la marea alta. Del mismo modo, el delfín costero utilizó áreas cercanas al margen del continente durante la marea alta. Los patrones de movimiento del delfín costero no presentaron relación con las corrientes de marea. Las franciscanas utilizaron áreas con más arena mientras que los delfines costeros prefirieron áreas lodosas; esta preferencia varió estacionalmente para ambas especies. Sugerimos que estos delfines modifican su distribución en base a la accesibilidad del hábitat y la disponibilidad de presas. Este estudio aumenta nuestro conocimiento sobre las características del hábitat crítico para la franciscana y el delfín costero, y estos factores deben ser considerados en la planificación de las actividades humanas locales orientadas a la conservación de estas especies.Palabras clave: ciclos de mareas; método de barrido; delfín franciscana; delfín costero; hábitat crítico; bahía Babitonga; Océano Atlántico SO.
The franciscana dolphin, Pontoporia blainvillei, is one of the most threatened cetaceans in the Southwestern Atlantic. Within their limited coastal range off Argentina, Uruguay, and Brazil, franciscanas face human activities, including artisanal gillnet fishing and coastal development. A lack of information on ranging patterns, population structure, and behavior for informing management led to efforts to develop and apply approaches to tag franciscanas in Argentina (Bahía Samborombón [BS], Bahía San Blas [BSB]) and Brazil (Baía Babitonga [BB]) during 2005–2013. Findings from VHF tags deployed in BS in 2005 during feasibility tests for catching and handling franciscanas for tagging suggested residency over periods of weeks. Subsequently, satellite‐linked tags confirmed patterns of residency at each site. Home range size varied, with ranges of 5–7 km2 for BB, 51–312 km2 for BS, and 49–1,014 km2 for BSB. Diving patterns varied across sites, with the animals using the entire water column, exposing them to fishing nets regardless of the depth at which the nets were set. Tracking durations and follow‐up observations indicated that this research approach is useful for studies of franciscanas. Small, definable ranges facilitate relating specific geographically based threats to appropriate population units, increasing the potential for effective conservation.
Environmental and ecological factors can trigger changes in the acoustic repertoire of cetaceans. This study documents the first use of a well-established passive acoustic monitoring device (C-POD) to analyze echolocation sounds and behavior of franciscana dolphins in different habitats: estuary [Babitonga Bay (BB)] and open sea [Itapirubá Beach (IB)]. A total of 10 924 click trains were recorded in BB and 6 093 in IB. An inter-click interval < 10 ms (so called “feeding buzzes”) was used as a proxy for foraging activity. The main difference in the acoustic parameters between the two habitats was related to the frequency spectrum, with higher maximum and lower modal and minimum click frequencies in BB, and a train frequency range of 17 kHz, against 10 kHz in IB. Also, the click emission rate (clicks/s) was almost 20% higher in BB. Both studied habitats showed a high proportion of feeding buzzes (BB = 68%; IB = 58%), but with a higher probability of occurrence in BB (p < 0.001) and at night (p < 0.001) in both habitats. The C-PODs showed great potential to monitor occurrence, bioacoustics parameters, and echolocation behavior of franciscana dolphins. Longer-term temporal and spatial monitoring are necessary for elucidating several issues raised in this study.
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