Surface patterns of Sotalia guianensis (Cetacea: Delphinidae) in the presence of boats in Port of Malhado, Ilheus, Bahia, Brazil

Abstract

ABSTRACT.Interactions with boats can cause several behavioural changes in cetaceans. The purpose of this research is to analyse if Guiana dolphins, Sotalia guianensis, change their surfacing patterns in the presence of different boat categories, and their contact distances to boats at Port of Malhado, Ilhéus, Bahia, Brazil. Data were collected from a fixed point from September 2008 to August 2009 and totalled 362.6 h of sampling effort and 213.22 h of effective effort. The number of dolphin breathing events was recorded during one minute periods, every time a boat passed nearby, and the same measurements were performed during periods of boat absence (control). Dolphin group composition was classified into groups with calves and groups without calves. Boat types were classified as inboard motor (IM), outboard motor (OM), ships (S) and without a motor (WM). Distances between the dolphins and passing boats were classified as near, intermediate and far. In total, 365 samples of one minute observations in absence of boats, and 379 observations in their presence were collected. Inboard motorboats had the highest occurrence in the study area (n = 478) and in interactions with Guiana dolphins (n = 260). However, outboard motorboats were mainly responsible for the reduction in surface patterns with an average of 1.82 and median of 2.2. In groups with calves, the number of breaths decreased significantly with an average of 2.13 per minute. There were no significant variations concerning the distances in the breathing pattern for any of the boat categories. The variation in the S. guianensis breathing pattern in the presence of boats may be a strategy of boat avoidance or a response to the difficulty of communication between animals.

Behavioral responses of Sotalia guianensis (Cetartiodactyla, Delphinidae) to boat approaches in northeast Brazil

“…Fewer surfacing events were performed by the dolphins in the presence of any boat type. Increased dive time during motorboat encounters was evidenced for this same population in the Port of Malhado, Ilhéus (Santos et al, 2013) and for different cetacean species: Chinese white dolphins (Ng & Leung, 2003), Irrawaddy dolphins (Orcaella brevirostris, Kreb & Rahadi, 2004), and bottlenose dolphins (Arcangeli & Crosti, 2009). These animals react to boat proximity with escape strategies, rising fewer times to the surface to reduce their exposure (Frid & Dill, 2002;, and moving away from the source of disturbance (Lusseau, 2003).…”

“…An encounter occurred when a boat was at a distance of fewer than 100 m from the closest dolphin. The 100 m distance of encounter definition was based on Valle & Melo (2006) and Santos et al (2013) studies on S. guianensis. Encounter distance was estimated visually since the duration of surfacing events of Guiana dolphins are too short for telemeter use.…”

“…These surfacing events were recorded for up to 10 min before (B) and 10 min after (A) the closest approaching moment of a boat for comparison purposes. The time of the first and last surfacing event was recorded to calculate 1) the mean frequency of surfacing events per individual and per minute (Santos et al, 2013), and 2) the Surfacing Index (SI). We employed the variable SI for the first time in the literature.…”

“…Toothed whales react to boat encounters with shortterm behavioral changes in an attempt to minimize their impact (Lusseau, 2006). For example, killer whales (Orcinus orca) swim faster (Williams et al, 2014); Guiana dolphins (Sotalia guianensis) breath at a decreased frequency (Santos et al, 2013) and increase breathing synchrony (Tosi & Ferreira, 2008); Hawaiian spinner dolphins (Stenella longirostris) perform a higher whistle activity (Heenehan et al, 2017) and bottlenose dolphins (Tursiops truncatus) alter their activity more frequently (Constantine et al, 2004) in the presence of boat. These short-term behavioral changes can lead to long-term alterations including population decline (Bejder et al, 2006) and abandonment of an area, as evidenced in a population of bottlenose dolphins in New Zealand (Lusseau, 2005).…”

Abundance and effect of health status on apparent survival of Guiana dolphins, Sotalia guianensis, in an open embayment in north‐eastern Brazil

“…Most of these coastal habitats have been occupied and significantly altered by human settlements and infrastructure (Meirelles, 2020;Schiavetti et al, 2020). Various human threats have been reported for the species, such as incidental capture in fishing gear (Monteiro-Neto et al, 2000;Meirelles et al, 2002;Crespo et al, 2010;Meirelles et al, 2010;Bertozzi, Silva & Flach, 2020), chemical pollution (Santos-Neto et al, 2014;Alonso et al, 2015;Dorneles et al, 2016;Lailson-Brito et al, 2020), noise pollution (Bittencourt et al, 2017;Pais et al, 2018;Rossi-Santos, Monteiro-Filho & Azevedo, 2020), unregulated dolphin-watching activities (Santos-Junior et al, 2006;Valle & Melo, 2006;Filla & Monteiro-Filho, 2009), boat traffic (Santos, Schiavetti & Alvarez, 2013;Schiavetti et al, 2020), and harbour operations, such as dredging (Meirelles, 2013). Infectious diseases such as morbillivirus (Groch et al, 2018;Flach et al, 2019), herpesvirus (Sacristán et al, 2018), brucellosis (Sánchez-Sarmiento et al, 2019), and toxoplasmosis (Silva et al, 2019) have been reported for Guiana dolphins and are of great concern, as outbreaks can cause mass die-offs (Carvalho et al, 2020).…”