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

Renan Lopes Paitach,Paulo César Simões-Lopes,Marta Jussara Cremer

doi:10.3989/scimar.04495.25a

Renan Lopes Paitach, Paulo César Simões-Lopes + Show 1 more

Open Access

https://doi.org/10.3989/scimar.04495.25a

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Abstract

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.

Highlights

Estuaries are influenced by tidal cycles, which include periodic variations in depth, direction, current speed, salinity, temperature and availability of flooded areas (McLusky and Elliott 2004)
Several studies have recognized the influence of tide on cetacean species distributions, behaviour and habitat use (e.g. Shane 1990, Bordino 2002), but few studies have aimed to describe these effects in detail (e.g. Mendes et al 2002, Fury and Harrison 2011, Lin et al 2013)
Table 2. – Mean and standard deviation of habitat use metrics for Pontoporia blainvillei in Babitonga Bay (February 2004 - August 2014) with bi-factorial ANOVA results testing for effects of tidal stage and season (*, significant values)

Summary

Introduction

Estuaries are influenced by tidal cycles, which include periodic variations in depth, direction, current speed, salinity, temperature and availability of flooded areas (McLusky and Elliott 2004). Fish and crustaceans often modify their distributions and behaviours in response to variation in these environmental factors (Reis-Filho et al 2011) These tidal migrations involve the movement of large numbers of species between locations synchronously with the tidal cycle (Gibson 2003). Identification of patterns of habitat use is key to our understanding of many ecological aspects of species biology, such as population trends and social dynamics (Krebs 2008). This knowledge is crucial for creating strategies that may minimize or mitigate human impacts upon natural environments (Hastie et al 2004). Hypotheses from optimal foraging theory (Perry and Pianka 1997) suggest that dolphins have lower spatial requirements in terms of area used when resource availability is higher

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