Killer whales (Orcinus orca) are marine apex predators distributed across the world’s oceans. In the last 40 years, researchers have increasingly differentiated killer whales into ecotypes based on genetics, morphology, behaviour, acoustic repertoire, habitat, and trophic ecology. While killer whale ecotypes in the Northern Hemisphere are well studied, the recognition of distinct killer whale forms in the Southern Hemisphere is mainly limited to Antarctic waters. Although present in less studied regions, such as along the Atacama Desert coast in the Southeast Pacific Ocean, limited information is available regarding their biology or trophic ecology. Herein, multiple lines of evidence are presented for killer whale predation on marine mammals in northern Chile. Using information from systematic boat-based surveys, whale-watching tour surveys, and reports from fishermen/citizen scientists, 19 killer whale sightings are reported along the coast of northern Chile (from the Arica and Parinacota region in the north to the Atacama region in the south). Killer whales were photo-identified as corresponding to the Southern Hemisphere Type A-like ecotype according to their dorsal fin shape and white eye patch. One killer whale pod, which included two males, one female, one juvenile, and one calf, was resighted six times from 2016 to 2021 in northern Chile and was observed hunting South American sea lions (Otaria flavescens), dusky dolphins (Lagenorhynchus obscurus), and long-beaked common dolphins (Delphinus cf. capensis). Killer whales were observed taking advantage of large aggregations of sea lions associated with the offshore purse-seine fishery. Adult killer whales used the hulls of fishing vessels to prevent sea lions from escaping. Photo-identification analysis of a fin whale (Balaenoptera physalus) catalogue from Mejillones Peninsula showed that 2.6% of all identified whales had apparent rake marks from killer whale teeth on their dorsal fins. These data show that Type A-like killer whales in northern Chile prey on several species of marine mammals.

Evidence of Type A-Like Killer Whales (Orcinus orca) Predating on Marine Mammals Along the Atacama Desert Coast, Chile

**The Intriguing Predatory Behavior of Killer Whales in Northern Chile**

Killer whales, also known as Orcas, are formidable predators that inhabit oceans across the globe. Although extensively studied in the Northern Hemisphere, Southern Hemisphere killer whale populations have received less attention. In particular, information about their biology and feeding habits in less explored regions, such as the coast of northern Chile, is scarce.

Recent research has shed light on the presence of killer whales in northern Chile and their predation on marine mammals. Through various sources, including systematic boat-based surveys, whale-watching tour surveys, and reports from fishermen and citizen scientists, researchers have documented 19 sightings of killer whales along the coastline, stretching from the Arica and Parinacota region in the north to the Atacama region in the south.

By analyzing the appearance of the killer whales' dorsal fins and white eye patches, researchers have identified these predatory creatures as belonging to the Southern Hemisphere Type A-like ecotype. A pod consisting of two male individuals, one female, one juvenile, and one calf was observed and tracked from 2016 to 2021 in the area. This pod was observed actively hunting South American sea lions, dusky dolphins, and long-beaked common dolphins.

Interestingly, the killer whales took advantage of the presence of large groups of sea lions that were associated with offshore purse-seine fishing operations. They cleverly used the hulls of fishing vessels to prevent the sea lions from escaping and successfully ambushed their prey. This behavior showcases the remarkable adaptability and resourcefulness of these marine predators.

Furthermore, researchers noticed that some fin whales in the area exhibited rake marks on their dorsal fins, seemingly caused by the teeth of killer whales. Analysis of a fin whale catalogue collected from Mejillones Peninsula revealed that approximately 2.6% of all identified whales had these distinct telltale signs of killer whale encounters. These findings provide additional evidence of killer whale predation in the region.

The significance of this research lies not only in shedding light on the predator-prey dynamics of killer whales in this particular region but also in expanding our knowledge of the ecology of Southern Hemisphere killer whale populations. By uncovering new information about their behavior, diet, and ecological interactions, we can gain a deeper understanding of the broader role killer whales play in marine ecosystems.

However, many questions still remain unanswered. What drives the distribution of killer whales in this region? Why do they specialize in hunting certain species? Are there any long-term implications for local marine mammal populations? Further investigation and continued monitoring of these killer whale communities are needed to unravel the complex web of life in the waters off northern Chile.

As we delve further into the study of marine ecosystems, each new discovery brings forth exciting possibilities and challenges our understanding of the natural world. The pursuit of knowledge about these majestic creatures continues to unfold before us, unraveling the mysteries of the depths one piece at a time.

Detecting killer whales preying on marine mammals in Chile