Distinctive, fine‐scale distribution of Eastern Caribbean sperm whale vocal clans reflects island fidelity rather than environmental variables

Abstract

Environmental variables are often the primary drivers of species' distributions as they define their niche. However, individuals, or groups of individuals, may sometimes adopt a limited range within this larger suitable habitat as a result of social and cultural processes. This is the case for Eastern Caribbean sperm whales. While environmental variables are reasonably successful in describing the general distribution of sperm whales in the region, individuals from different cultural groups have distinct distributions around the Lesser Antilles islands. Using data collected over 2 years of dedicated surveys in the Eastern Caribbean, we conducted habitat modeling and habitat suitability analyses to investigate the mechanisms responsible for such fine‐scale distribution patterns. Vocal clan‐specific models were dramatically more successful at predicting distribution than general species models, showing how a failure to incorporate social factors can impede accurate predictions. Habitat variation between islands did not explain vocal clan distributions, suggesting that cultural group segregation in the Eastern Caribbean sperm whale is driven by traditions of site/island fidelity (most likely maintained through conformism and homophily) rather than habitat type specialization. Our results provide evidence for the key role of cultural knowledge in shaping habitat use of sperm whales within suitable environmental conditions and highlight the importance of cultural factors in shaping sperm whale ecology. We recommend that social and cultural information be incorporated into conservation and management as culture can segregate populations on fine spatial scales in the absence of environmental variability.

Cetacean Sociality, Reproduction, and Conservation

“…Many cetacean species are highly mobile and frequently move across arbitrary national or other jurisdictional boundaries. Even within a single species, we find variation in residency and ranging patterns (e.g., sperm whales, Vachon et al 2022;killer whales, Ford 2019; common bottlenose dolphins (Tursiops truncatus), Oudejans et al 2015). Yet, researchers in different regions of the world often have vastly different levels of access to resources (financial, technical, etc.…”

Sperm whale clans and human societies

“…Evidence for behavioural and other differences between sperm whale clans using the same areas. trait strength of evidence references coda dialect excellent [20,[33][34][35][36]39] geographical extent excellent [20,29,39] small-scale distributions (10's km) good [25,44] large-scale movements (days-years) good [28,29] small-scale movements (hours) good [23,29] feeding success good [23] changes in feeding success with El Niño ok [23] reproductive rates ok [24] diving synchrony (babysitting) ok [26] homogeneity of social relationships within social units ok [26] duration of social relationships indication [26] diet indication [27] 1…”

“…What were these clans?

Figure 1Identity codas (stereotypical patterns of clicks made primarily by one clan) of clans in the Atlantic and Pacific (data from Figure 6.2 of [62], in which the codas from Atlantic and Pacific clans are combined in one analysis). Note: the identity codas of EC1 all contain five clicks and are of the form ‘click-{pause}-click-{pause}-click-click-click’.

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“…The known Dominica whales were rarely found far from Dominica, and different islands had either very predominantly EC1 or very predominantly EC2 social units [ 29 ]. Differences in distribution between the clans could not be explained by differences in habitat features, but rather the vicinity of clans to particular islands themselves (most likely caused by the traditions of social units, closely linked to their clan membership) [ 44 ]. As a dramatic example, the waters off Martinique, just 30 km from EC1-dominated Dominica, contain almost entirely EC2 social units.…”

Acoustic estimates of sperm whale abundance in the Mediterranean Sea as part of the ACCOBAMS Survey Initiative

“…In addition to latitude and longitude, several bathymetric and oceanographic parameters were used to generate the DSM (Table 1) and were selected on the basis of their potential to influence sperm whale distribution and their availability for the whole survey area. These parameters have been linked to sperm whale distribution in other studies, and included depth (Cañadas et al, 2005;Pirotta et al, 2011;Mannocci et al, 2017b;Pace et al, 2018;Pirotta et al, 2020), slope (Cañadas et al, 2005;Praca and Gannier, 2008;Pirotta et al, 2011;Pirotta et al, 2020), aspect (Pirotta et al, 2011;Pirotta et al, 2020), SST (Cañadas et al, 2005;Praca and Gannier, 2008;Pirotta et al, 2011;Pirotta et al, 2020), chlorophyll (Jaquet et al, 1996;Praca and Gannier, 2008;Mannocci et al, 2017b), distance to isobath (including 0, 200 and 1,000 m; Praca and Gannier, 2008;Pace et al, 2018;Sahri et al, 2020;Avila et al, 2022), distance to bathymetric features (such as canyons, escarpments, ridges, seamounts, shelves, slopes, terraces and troughs; Mannocci et al, 2017b;Sahri et al, 2020;Vachon et al, 2022), mixed layer thickness (Avila et al, 2022) and local currents (Vachon et al, 2022). Dynamic oceanographic parameters, such as SST, chlorophyll, depth of mixed layer and water speed/direction, can vary at timescales from seconds to decades.…”