Dusky dolphin group dynamics and association patterns in Península Valdés, Argentina

Abstract

We inspected dusky dolphin (Lagenorhynchus obscurus) group dynamics in Golfo Nuevo and found differences in social organization between cold and warm seasons. Surveys were conducted onboard a research vessel, from which we collected behavioral observations and group fission‐fusion data from 2001 to 2008; we also collected photo‐identification data from 2004 to 2012. To analyze association patterns, we calculated half‐weight association index (HWI) and social differentiation (S). We conducted a Monte Carlo permutation test to determine whether observed association patterns were significantly different from random association using a compiled version of SOCPROG 2.7. Group fission and fusion dynamics depended on group behavior, the main activity after the groups' fusion was feeding, and they never fission before socializing. The social structure of dusky dolphins included long‐term preferred companions in the cold season; during the warm season, there were no preferred companions. This seasonal difference in social structure could be related to an accompanying shift in foraging behaviors that appears to be driven by changes in prey availability. If so, then a loosening of bonds among individuals during the warm season, when prey is more available, would reflect these social structure changes.

Intra-Population Variability in Group Size of Indo-Pacific Humpback Dolphins (Sousa chinensis)

“…Such positive impact of nursery behavior on enlarging group size has not only been reported for the IPHDs in the eastern Taiwan Strait (Dungan et al, 2016), and also for other dolphin species such as bottlenose dolphins (Tursiops spp.) (Gibson and Mann, 2008b), dusky dolphins (Lagenorhynchus obscurus Gray, 1828) (Degrati et al, 2019), and Guiana dolphins (Sotalia guianensis) (Azevedo et al, 2005;Santos and Rosso, 2007;Emin-Lima et al, 2010). This social strategy i.e., dolphin group became larger when calves were present, could bring a variety of added benefits such as enhanced calf-assistance, cooperative calf-caring, reduced maternal investments, and increased calf-protection (against predators or intraspecific aggression) (Mann et al, 2000;Gibson and Mann, 2008a;Kent et al, 2008).…”

“…This increase in feeding, traveling, or socializing group size has been reported for the bottlenose dolphins (Heithaus and Dill, 2002), common dolphins (Delphinus spp.) (Neumann, 2001;Stockin et al, 2009), and dusky dolphins (Degrati et al, 2019). IPHDs tended to form large, temporary, and functional gathering of different social units when they were not resting or milling (Würsig et al, 2016), which might help strengthen group added benefits (Baird and Dill, 1996;Neumann, 2001;Yeater et al, 2013).…”

“…Intra-specific variability in IPHD group sizes is not fully investigated, although some previous studies have basically described social characteristics of humpback dolphins. Previous studies suggested dolphin group sizes and composition may be associated with species characteristics, habitat structure, and social-environmental aspects of populations (Baird and Dill, 1996;Gibson and Mann, 2008b;Degrati et al, 2019). Changes in humpback dolphin group size, such as annual (Koper et al, 2016), seasonal (Chen et al, 2011;Wang et al, 2016), and behavioral variations (Würsig et al, 2016), are often habitat-specific and affected by a series of environmental variables at a regional scale.…”

Diversity and Consequences of Social Network Structure in Toothed Whales

“…In common bottlenose dolphins (T. truncatus), for example, reported values range from 0.29 in Bahia San Antonio (Vermeulen, 2018) to 1.08 in the northern Adriatic Sea (Genov et al, 2019). Some studies have also reported variations within populations between seasons, such as dusky dolphins (Lagenorhynchus obscurus) in Golfo Nuevo, where social differentiation is considerably higher during the winter (Degrati et al, 2018).…”

Integrating Multiple Techniques to Estimate Population Size of an Impacted Dusky Dolphin’s Population in Patagonia, Argentina

“…Only adult and juvenile dolphins with a pattern of nicks and notches along the trailing edge of a dorsal fin to allow future No. biopsied dolphins --5 ( 2) 4 ( 1) 20 ( 7) 2 ( 1) 5 (3) -17 ( 6) 3 (1) 14 ( 7) 13 (2) ---re-identification were included in the photo-identification data set (Degrati et al, 2019b).…”