Tidal and seasonal influences in dolphin habitat use in a southern Brazilian estuary

Abstract

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.

Tagging, ranging patterns, and behavior of franciscana dolphins (Pontoporia blainvillei) off Argentina and Brazil: Considerations for conservation

“…Movements relative to tides were observed in all the studied areas, with different intensities. For Bahía San Blas and Baía Babitonga, movement patterns associated with tides were previously reported in studies based on visual observations (Bordino, 2002;Paitach et al, 2017). Movements with the current may be associated with lower energy consumption, resulting in greater travel speed, and may also be related to hunting strategies, where tidal cycle may influence the accessibility of prey or ability to capture prey in different ways, affecting habitat use of franciscana dolphins (Bordino, 2002;Paitach et al, 2017).…”

“…In southern Brazil, Danilewicz et al (2009) suggested that there is no segregation in franciscana distribution related to reproductive status, sex or age, based on data obtained throughout the year. However, in Baía Babitonga, Paitach et al (2017) calculated larger franciscana home ranges during the winter than during the summer, but no difference between seasons was observed for core ranges. This may indicate that even though franciscanas in Baía Babitonga use a larger extent of their home range during the winter months, the most important areas for the population remain unchanged.…”

“…In Bahía San Blas, in southern Argentina, franciscana dolphin sightings were made from shore-based sites and movements in and out of the bay were strongly related to tidal cycle (Bordino, 2002). The influence of the tide on the movements of the species was also recorded in Baía Babitonga, Brazil, where the franciscanas remained closer to the bay mouth at the end of ebb tide, and shifted with the current in favor of inner areas of the bay at the end of the flood tide (Paitach et al, 2017).…”

Modelling habitat use by the Guiana dolphin, Sotalia guianensis, in south‐eastern Brazil: Effects of environmental and anthropogenic variables, and the adequacy of current management measures

“…Seasonal variation in habitat use has been recorded in Guiana dolphin populations from other areas, such as Norte Bay, in southern Brazil (Wedekin, Daura‐Jorge, & Simões‐Lopes, ) and the Cananéia estuarine lagoon complex in south‐eastern Brazil (Godoy et al, ). However, no clear seasonal pattern was detected in Babitonga Bay, in southern Brazil (Paitach, Simões‐Lopes, & Cremer, ).…”

Monitoring Indo‐Pacific humpback dolphin occurrences in a highly urbanized estuary for informing conservation and management

“…Tides have also been identified as an important environmental factor for coastal delphinids in terms of habitat use (Goodwin, 2008; Fury & Harrison, 2011; Paitach, Simões‐Lopes & Cremer, 2017). This also includes humpback dolphins, with more click trains being detected during the flood tide rather than slack high tide in the PRE (Wang et al, 2015), and lower acoustic encounter rates seen during the ebb tide in the Xin Huwei Estuary in Taiwan (Lin, Akamatsu & Chou, 2013).…”