Evidence for Distinct Coastal and Offshore Communities of Bottlenose Dolphins in the North East Atlantic

Abstract

Bottlenose dolphin stock structure in the northeast Atlantic remains poorly understood. However, fine scale photo-id data have shown that populations can comprise multiple overlapping social communities. These social communities form structural elements of bottlenose dolphin (Tursiops truncatus) populations, reflecting specific ecological and behavioural adaptations to local habitats. We investigated the social structure of bottlenose dolphins in the waters of northwest Ireland and present evidence for distinct inshore and offshore social communities. Individuals of the inshore community had a coastal distribution restricted to waters within 3 km from shore. These animals exhibited a cohesive, fission-fusion social organisation, with repeated resightings within the research area, within a larger coastal home range. The offshore community comprised one or more distinct groups, found significantly further offshore (>4 km) than the inshore animals. In addition, dorsal fin scarring patterns differed significantly between inshore and offshore communities with individuals of the offshore community having more distinctly marked dorsal fins. Specifically, almost half of the individuals in the offshore community (48%) had characteristic stereotyped damage to the tip of the dorsal fin, rarely recorded in the inshore community (7%). We propose that this characteristic is likely due to interactions with pelagic fisheries. Social segregation and scarring differences found here indicate that the distinct communities are likely to be spatially and behaviourally segregated. Together with recent genetic evidence of distinct offshore and coastal population structures, this provides evidence for bottlenose dolphin inshore/offshore community differentiation in the northeast Atlantic. We recommend that social communities should be considered as fundamental units for the management and conservation of bottlenose dolphins and their habitat specialisations.

Quantifying dispersal between marine protected areas by a highly mobile species, the bottlenose dolphin,Tursiops truncatus

“…Furthermore, social structure analyses using long‐term photo‐identification data revealed that the two coastal populations were not only genetically, but also socially, distinct. This kind of social separation has been previously reported between the “ pelagic” and “ coastal” bottlenose dolphins (Oudejans, Visser, Englund, Rogan, & Ingram, ).…”

Identifying the Relevant Local Population for Environmental Impact Assessments of Mobile Marine Fauna

“…These differences may be related to the difference in habitat structure and prey (Queller and Goodnight, 1989) for within-community (bold) and with individuals from other communities of bottlenose dolphins (between-community) genotyped with 10 microsatellite loci in Perth metropolitan waters, WA. (Defran and Weller, 1999;Oudejans et al, 2015;Sprogis et al, 2015). Here, individuals from the GR community (ComA) showed no residency pattern, with most identified individuals seen less than five times and LIR models indicating that individuals spent more time outside the study area.…”

Occurrence, site fidelity, and associations of oceanic common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand

“…Range overlap appears less frequent in other regions, with the oceanic ecotype not typically encountered nearer than a few kilometers from shore, e.g., >4 km in the Northeast Atlantic; Oudejans et al, (2015); >7.5 km in the Northwest Atlantic; Hayes, Josephson, Maze-Foley, & Rosel, (2017). However, parapatric distribution comparable to that observed in the present study has been documented in places including the western South Atlantic (Simões-Lopes et al, 2019) and the eastern North Pacific (Bearzi et al, 2009) where the coastal ecotype does not normally venture more than 3 and 1 km from shore, respectively.…”

“…Distinct populations of nearshore (or coastal) and offshore (or oceanic) common bottlenose dolphins (hereafter referred to as coastal and oceanic bottlenose dolphins, respectively) are known to occur across the species' range (e.g., Duffield, Ridgway & Cornell, 1983; Hoelzel et al, 1998; Mead & Potter, 1995; Oudejans, Visser, Englund, Rogan, & Ingram, 2015; Rossbach & Herzing, 1999). Differences in habitat, morphology, hematology, genetics, diet, parasitic load, and behavior between the two ecotypes have been reported from multiple sources (e.g., Duffield et al, 1983; Hersh & Duffield, 1990; Hoelzel et al, 1998; Lowther‐Thieleking, Archer, Lang, & Weller, 2015; Mead & Potter, 1995; Morteo, Morteo, & Rocha‐Olivares, 2005; Perrin, Thieleking, Walker, Archer, & Robertson, 2011; Sanino & Van Waerebeck, 2008; Simões‐Lopes et al, 2019; Toth, Hohn, Able & Gorgone, 2012; Visser et al, 2010), despite suggested parapatry (Hoelzel et al, 1998) in some areas.…”