Spatial behavioural response of coastal bottlenose dolphins to habitat disturbance in southern Brazil

Abstract

A small population of coastal bottlenose dolphins (Tursiops truncatus gephyreus) inhabits the inland waters of Laguna, southern Brazil. A subset of this population interacts with artisanal fishermen. This specialized foraging tactic structures dolphin society into ‘cooperatives' (participants of the interaction) and ‘non‐cooperatives' (non‐participants). Between 2012 and 2015, a bridge was constructed in Laguna over an important core area for dolphins. Photo‐identification and georeferenced data collected on boat surveys, conducted both before and during bridge construction, were used to evaluate changes in both ‘cooperative' and ‘non‐cooperative' dolphin distribution. Changes in dolphin distribution were analysed with kernel densities and hurdle models. A grid of 120 cells of area 1 km2 was used to model dolphin distribution, and the minimum distance from the grid cell centre to the bridge and to the area of gillnet use were defined as explanatory variables of human activities. Habitat descriptors (depth and distance) from the lagoon margin were also considered in the model procedure. Dolphin distribution patterns shifted between periods. A core area used by ‘non‐cooperative' dolphins near the bridge construction works disappeared. The effects of habitat descriptor and anthropogenic activity on dolphin distribution also differed between periods. Before bridge construction, the abundance of ‘non‐cooperative' dolphin was higher close to the bridge area (p < 0.05). During bridge construction, the presence of ‘cooperative' and ‘non‐cooperative' dolphins decreased significantly with the distance from gillnet fishing activity (p < 0.01 and p < 0.001 respectively). This study highlights the importance of accounting for individual variations in response when assessing the effects of a habitat disturbance, or when implementing conservation plans.

An Ethology of Adaptation: Dolphins Stop Feeding but Continue Socializing in Construction-Degraded Habitat

“…Cetacean displacements from previous foraging grounds are well-established responses implicating the dispersive effects of construction-related noise pollution, dredging, and pile driving (Carrera et al, 2008;Miller et al, 2009Miller et al, , 2012Thompson et al, 2010;Pirotta et al, 2013Pirotta et al, , 2015Paiva et al, 2015;Marley et al, 2017;Wisniewska et al, 2018;Agrelo et al, 2019;Kreb et al, 2020). Significant reductions in foraging and feeding in this study confirmed reports that construction displaces cetaceans Total groups = total number of dolphins groups encountered in John's Pass in the immediate construction zone.…”

Safeguarding human–wildlife cooperation

“…Laws against fishing practices that can kill dolphins are rarely enforced (Bezamat et al., 2021; Smith et al., 2009). Habitat disturbance (such as dredging and construction for coastal and riverine development) can change dolphins’ habitat use, leading to temporary or permanent abandonment of important areas, including where dolphins and fishers cooperate (Agrelo et al., 2019). While honeyguides are widespread across sub‐Saharan Africa and their conservation status is Least Concern (IUCN, 2021), they are brood parasites and so rely on other species to raise their young, making them vulnerable to any threats affecting their host species.…”

Effects of swim‐with‐dolphin tourism on the behaviour of spinner dolphins, at Samadai Reef in the Egyptian Red Sea

“…show reduced resting and socializing (Lundquist, Sironi, Würsig, & Rowntree, 2008). Not only may dolphins move away from cetaceanwatching boats, but they show changes in their diving and surfacing patterns, in their activity budget (Constantine & Baker, 1997;Constantine, Brunton, & Dennis, 2004;Lusseau, 2003;Meissner et al, 2015;Neumann & Orams, 2006;Peters, Parra, Skuza, & Möller, 2012;Stensland & Berggren, 2007;), and in their resting (Heenehan, Van Parijs, Bejder, Tyne, & Johnston, 2017), grouping Heiler, Elwen, Kriesell, & Gridley, 2016;Nowacek et al, 2001), and home-range behaviour (Agrelo et al, 2019).…”