Social structure of killer whales (Orcinus orca) in a variable low‐latitude environment, the Galápagos Archipelago

Abstract

Killer whales (Orcinus orca) have strong social matrilineal bonds and form groups and long‐lasting associations, but little is known about their population or social structure in an equatorial setting such as the waters around the Galápagos Islands. Using 91 encounters and identification photographs from 1991 to 2017, we identified 64 killer whales of which 18 individuals were locals with high resighting rates. Group size was small, ranging from 1 to 15 animals, with 69% of the groups containing four or fewer animals. Using social network analysis (SOCPROG 2.7) whales grouped into three distinct units and one loose association with frequent exchange between different groups. One male–male unit showed a strong association (association strength = 0.55). Overall, associations lasted over at least 3 years. Our data give first evidence of a loose social organization of Galápagos killer whales, similar to fission‐fusion societies.

Ecological aspects of killer whales from the Mexican Central Pacific coast: Revealing a new ecotype in the Eastern Tropical Pacific

“…The diversity of prey items suggests that KW within the Mexican Pacific are generalist predators, which differs from the specialist ecotypes found in the ENP (Dahlheim et al, 2008;Ford et al, 1998;Herman et al, 2005;Krahn et al, 2007). However, a similar generalist predatory behavior was suggested for KW from Caribbean (Bolaños-Jiménez et al, 2014), New Zealand (Visser & Mäkelänen, 2000), and most recently for KW from the ETP (Testino et al, 2019), and from the Galápagos Archipelago (Denkinger et al, 2020), where the existence of KW ecotypes remains unclear .…”

“…However, inferring that ETP mammal-eating KW are "transient" could be wrong. First, the reported feeding behavior of KW groups from the ETP indicates that they do not feed exclusively on marine mammals; they also prey on sea turtles, elasmobranchs (sharks and manta rays), and bony fish (Guerrero-Ruiz, 1997;Guerrero-Ruiz, Urbán, Gendron, & Rodríguez, 2007;Pacheco et al, 2019;Sánchez-Díaz & Meráz, 2001); as has been suggested for tropical populations of KW elsewhere (Denkinger et al, 2020). Second, photographic matches between KW individuals from the ENP and the ETP have been limited to a few individuals, and no "transient" KW populations have been documented further south than California; therefore, it has been suggested that there is a southern distribution boundary for KW from the ENP (Black, Schulma-Janiger, Ternullo, & Guerrero-Ruiz, 1997).…”

A new sighting of killer whale, Orcinus orca, in Caribbean inshore waters off Colombia

“…Whenever the pod size surpasses the optimum maximizing energy, subadult males often disperse permanently and become loners (Baird and Dill 1995, Baird and Whitehead 2000, Ford and Ellis 2006, Dalla-Rosa and Secchi 2007. This is the case for sightings in the Caribbean (Bolaños-Jiménez et al 2014) and other tropical areas, such as Perú (García-Godos 2004), Brazil (Lodi and Farias-Junior 2011), and the Galápagos Islands (Denkinger et al 2020). Since no ecotype has yet been determined for Caribbean killer whale populations, it is likely their structure and behavior resemble the transient type.…”

Fission–fusion dynamics of a pelagic delphinid in the arctic: the white‐beaked dolphin (Lagenorhynchus albirostris)

“…Social structure within and between cetacean species is quite varied depending on a number of factors including environmental conditions, habitat preference, human pressures, and presence of predators (Rendell et al 2019). Consequently, there is variation among cetacean species as shown by the community of bottlenose dolphins of Doubtful Sound, New Zealand, showing long-lasting and constant associates (Lusseau et al 2003) and by orcas around the Galápagos Islands (Denkinger et al 2020) characterized by fission-fusion dynamics. It is vital to focus on the range of species and environments, especially those extreme changing habitats like the one inhabited by white-beaked dolphins (Lagenorhynchus albirostris) in Iceland.…”

“…2003) and by orcas around the Galápagos Islands (Denkinger et al . 2020) characterized by fission–fusion dynamics. It is vital to focus on the range of species and environments, especially those extreme changing habitats like the one inhabited by white‐beaked dolphins ( Lagenorhynchus albirostris) in Iceland.…”