Fine scale spatial variability in the influence of environmental cycles on the occurrence of dolphins at coastal sites

Abstract

Environmental cycles often influence the presence of animals, creating patterns at different temporal scales, which may mean that their effects overlap and/or interact. Interactions between diel and seasonal cycles have been reported to influence fish behaviour but little is known about such interactions in marine top predators. Here, we studied the combined effect of seasonal, tidal and diel cycles on the occurrence of bottlenose dolphins ( Tursiops truncatus ) within a Marine Protected Area in Scotland. Our analyses were based on echolocation detections from passive acoustic devices (CPODs) deployed at three coastal sites between 2010 and 2016. We described patterns of dolphins’ occurrence using circular statistics and then used generalised additive mixed models to explore the relative importance of each cycle and any interactions between them. We found site-specific cyclical patterns of presence that remained constant across years. There was a highly significant interaction between seasonal and diel cycles at two sites around deep channels, where occurrence was diurnal in summer but became nocturnal in autumn. The study demonstrates the highly plastic behaviour of bottlenose dolphins and shows a previously unreported behaviour that has management implications for this and other marine protected areas.

Far-Field Effects of Impulsive Noise on Coastal Bottlenose Dolphins

“…During the construction of Beatrice wind farm, a decrease was detected in the same area and during the construction of Moray East wind farm, no significant difference was detected. In line with previous studies, dolphin detections overall were higher in the Reference Area of the inner Moray Firth, compared with the Impact Inner area on the southern coast, but the extent of use varied between years and through the season (Thompson et al, 2015;Fernandez-Betelu et al, 2019). The difference in detections at the medium temporal scale therefore seems likely to be related to the natural inter-annual variation in occurrence that was also reflected in our analyses here (Figure 2).…”

“…CPODs were deployed between 2009 and 2019 following previously described techniques (Bailey et al, 2010a;Thompson et al, 2013;Graham et al, 2019). Two CPODs were deployed at sites within the inner Moray Firth where the impact was expected to be lowest; hereafter the Reference Area (Figure 1; Fernandez-Betelu et al, 2019). These reference sites were located at minimum distances of 42, 80, and 78 km from the seismic survey, Beatrice and Moray East wind farm developments, respectively.…”

“…With this array we aimed to investigate whether dolphins from further out at sea were displaced toward the coast in the southern Moray Firth by impulsive noise. Although data were collected year round at some locations, data from November to April were excluded from all the analyses due to the low occurrence of dolphins during those months along the southern Moray Firth coast (Fernandez-Betelu et al, 2019). CPOD data were downloaded and trainfiltered using the manufacturer's software 1 to identify which echolocation clicks were produced by dolphins.…”

Environmental drivers of habitat use by common bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon, Florida, USA

“…Finer temporal and spatial scale sampling of common bottlenose dolphin occurrences and concomitant sampling of currents, temperature, and prey patterns are required to obtain a greater understanding of the influence of these local and short-term effects on habitat use, resilience to disturbances, and trophic interactions. Accurate spatial and temporal information on dolphin distributions and stressors is required for planning and implementation of management and protection measures of these mobile species in coastal waters (Fernandez-Betelu et al, 2019). Given such data, managers may be better positioned to anticipate the success or detrimental impacts to dolphin cohorts or communities from either restoration or degradation of particular resources.…”

Acoustic Monitoring of a Bottlenose Dolphin (Tursiops truncatus) Population: Trends in Presence and Foraging beyond the Limits of the Lower River Shannon SAC

“…Based on the results of the Levesque et al [1] surveys as well as previous research showing fine-scale variation in habitat use by bottlenose dolphin populations within the Cardigan Bay SAC in Wales and the Moray Firth SAC in Scotland, it was hypothesized that bottlenose dolphins would be detected at the three study sites and that the drivers of presence and foraging would be site specific [16,17].…”