Intraspecific variation in the feeding habits of short-finned pilot whales based on blubber fatty acid profiles.

Understanding trophic interactions in deep-sea ecosystems is challenging and still largely unexplored. Here, fatty acid (FA) profiles were used as biochemical tracers to explore intraspecific feeding specialization in a deep-diving apex predator. The FA profiles of free-ranging short-finned pilot whale (Globicephala macrorhynchus) biopsies from two archipelagos (Canary Islands, n = 30; Madeira Island, n = 25) of the Macaronesia biogeographic region were determined to infer the dietary preferences, ecological adaptations, and population dynamics, considering geographic location, sex, and residency patterns (HIA: highly island-associated vs. "others": visitors or transients). Intraspecific variability (inferred through the representation of PERMANOVA analyses) was observed between HIA groups from the two archipelagos which exhibited distinct trophic niches. The "others" FA profiles largely overlapped with both groups, showing significant differences with HIA from the Canary Islands. This suggests that the "others" travel and forage across a broader area, likely encompassing these archipelagos. The differences between archipelagos were mainly attributed to a higher presence of the FA 20:1n-11 and 22:1n-11 in the animals from the Canary Islands, in contrast with a higher presence of 22:6n-3, 22:5n-3 and 20:5n-3 in the animals from Madeira. These findings suggest that short-finned pilot whales in Madeira may prefer a more pelagic diet, likely leveraging on nocturnal migrations of the Deep Scattering Layer and/or performing wider-ranging movements, while the animals in the Canary Islands may forage closer to the bottom and/or occupy a smaller core area. Overall, this study supports intraspecific feeding specialization by a deep-diving apex predator in two geographically related oceanic archipelagos.