Community structure and cluster definition of Atlantic spotted dolphins, Stenella frontalis, in the Bahamas

Abstract

Fission‐fusion dynamics typical of many delphinid populations allow for a variety of social grouping patterns. Identifying these groupings is crucial before conducting a detailed social structure analysis. This study analyzed the structure of a population of Bahamian spotted dolphins, Stenella frontalis. Through long‐term observations and preliminary analysis, three clusters were defined: Northern, Central, and Southern. To quantitatively investigate these delineations, we conducted analysis on 12 yr of sighting data using SOCPROG 2.3. Coefficients of association (CoA) were calculated using the half‐weight index, with individuals sighted six or more times per pooled period (3 yr each). Nonmetric multidimensional scaling (MD), hierarchical agglomerative cluster analysis and Mantel tests were conducted to determine if any divisions were present. Mantel tests and MD plots analysis supported the delineations into the three clusters. Cluster analysis showed cluster groupings, but with less clear distinctions between the clusters. The amount and strength of associations were significantly higher within clusters than between clusters. Based on behavioral and geographic overlap, these clusters did not meet the definition of separate communities and thus were termed social clusters. These fine scale, within community divisions, are biologically and socially important aspects of their community and are crucial in understanding the dolphins’ social structure.

Nocturnal feeding of Atlantic spotted dolphins (Stenella frontalis) in the Bahamas

“…Age, sex, and reproductive status were not limiting factors in the exploitation of deep‐water resources off the shallow Bahamas sandbanks since males and females of all age classes, including newborns and calves and females of different reproductive states (nonreproductively active, pregnant, and nursing with a calf) engaged in nocturnal feeding in deep water. The sex and age class composition of groups, the majority including all age classes, is consistent with daytime encounters including all behaviors (Elliser and Herzing ).…”

“…On the shallow banks of the Bahamas, a resident community of over 200 individually identifiable Atlantic spotted dolphins ( S. frontalis ) has been studied extensively for over two decades from May through September every year (Herzing , ; Herzing and Johnson ; Elliser and Herzing ). These dolphins have been observed on the shallow sandbank during daytime hours feeding on a variety of prey items including both burrowing and schooling fish (Families: Bothidae , Clinidae , Labridae , Hemiramphidae , Exocoetidae ; see Herzing ).…”

Mother-Offspring Signature Whistle Similarity and Patterns of Association in Atlantic Spotted Dolphins (Stenella frontalis)

“…Degree of association between two individuals in this type of fluctuating social environment can be quantified by a coefficient of association (COA). The COAs of this population were previously determined using the half-weight index (HWI) and SOCPROG modeling software (version 2.3) (Elliser & Herzing, 2012Welsh & Herzing, 2008). Analysis with the HWI provided a value between 0 and 1 for each dyad, based on how often two individuals are seen together and how often they are seen separately (Cairns & Schwager, 1987).…”

“…Analysis with the HWI provided a value between 0 and 1 for each dyad, based on how often two individuals are seen together and how often they are seen separately (Cairns & Schwager, 1987). Individuals were considered to be associating if they were observed in the same group (spotted: Elliser & Herzing, 2012;Welsh & Herzing, 2008).…”

Exploration of Horizontal Information Transmission through Social Learning in Juvenile Atlantic Spotted Dolphins (Stenella frontalis)

“…The bottom is primarily sandy, with zones of rock, reef and patches of seagrass (Thalassia testudimum). The life history, including non-invasive genetic analysis, (Elliser & Herzing, 2012, 2013, 2016a, 2016bGreen, Herzing & Baldwin, 2007 and the development and use of social and acoustic behaviors of this community of Atlantic spotted dolphins have been documented extensively Herzing, 2000Herzing, , 2004Herzing, , 2005Herzing & Brunnick, 1997;Herzing & dos Santos, 2004;Herzing & Johnson, 1997;Herzing, Moewe & Brunnick, 2003;Lammers, Au & Herzing, 2003;Miles & Herzing, 2003;Welsh & Herzing, 2008).…”