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

Ann Weaver

doi:10.3389/fmars.2021.603229

Abstract

Adaptation is a biological mechanism by which organisms adjust physically or behaviorally to changes in their environment to become more suited to it. This is a report of free-ranging bottlenose dolphins’ behavioral adaptations to environmental changes from coastal construction in prime habitat. Construction was a 5-year bridge removal and replacement project in a tidal inlet along west central Florida’s Gulf of Mexico coastline. It occurred in two consecutive 2.5-year phases to replace the west and east lanes, respectively. Lane phases involved demolition/removal of above-water cement structures, below-water cement structures, and reinstallation of below + above water cement structures (N= 2,098 photos). Data were longitudinal (11 years: 2005–2016,N= 1,219 surveys 2–4 times/week/11 years,N= 4,753 dolphins, 591.95 h of observation in the construction zone, 126 before-construction surveys, 568 during-construction surveys, 525 after-construction surveys). The dependent variable was numbers of dolphins (count) in the immediate construction zone. Three analyses examined presence/absence, total numbers of dolphins, and numbers of dolphins engaged in five behavior states (forage-feeding, socializing, direct travel, meandering travel, and mixed states) across construction. Analyses were GLIMMIX generalized linear models for logistic and negative binomial regressions to account for observation time differences as an exposure (offset) variable. Results showed a higher probability of dolphin presence than absence before construction began, more total dolphins before construction, and significant decreases in the numbers of feeding but not socializing dolphins. Significant changes in temporal rhythms also revealed finer-grained adaptations. Conclusions were that the dolphins adapted to construction in two ways, by establishing feeding locations beyond the disturbed construction zone and shifting temporal rhythms of behaviors that they continued to exhibit in the construction zone to later in the day when construction activities were minimized. This is the first study to suggest that the dolphins learned to cope with coastal construction with variable adjustments.

Highlights

The accelerating pace and breadth of marine coastal development threatens marine mammals with cumulative effects from unsustainable human practices and pollution (Williams et al, 2015; Gomez et al, 2016; Shannon et al, 2016; Avila et al, 2018)
The entire study area, starting with the construction zone, was surveyed 2–4 times a week from 2005 to 2016, subtotals of 94– 136 surveys/year, a total of N = 1,219 surveys, N = 4,753 dolphins observed in the construction zone, and a total N = 15,456 dolphins observed in the entire study area
This research provides a longitudinal perspective on the cumulative impacts of coastal construction

Summary

Introduction

The accelerating pace and breadth of marine coastal development threatens marine mammals with cumulative effects from unsustainable human practices and pollution (Williams et al, 2015; Gomez et al, 2016; Shannon et al, 2016; Avila et al, 2018). Noise drowns out or masks vocalizations, forcing animals to wait for noise pollution to subside or to invest more energy in communication, i.e., the Lombard effect (Jensen et al, 2008; May-Collado and Quiñones-Lebrón, 2014; Erbe et al, 2016; Gomez et al, 2016). Because they depend on sound, cetaceans may suffer more stress from noise pollution than most terrestrial species (Wright et al, 2007), but the impact of noise pollution varies by species. A review of experimental exposures to sonar by Southall et al (2016) provided causal evidence that even controlled doses of noise pollution (controlled to minimize long-term impacts) changed free-ranging cetaceans’ current activities to avoidance (DeRuiter et al, 2013; Goldbogen et al, 2013; Isojunno et al, 2016)

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