Energetic requirements and prey consumption of five different-sized cetaceans in Icelandic waters

Securing enough energy for maintenance, movement, and storage is fundamental to animal survival. Cetaceans face this challenge in the marine environment where prey availability varies, with some species feeding year-round and others only during brief seasonal periods. Here, we estimated energetic requirements and prey consumption for five cetacean species inhabiting the productive subarctic waters around Iceland: harbour porpoises ( Phocoena phocoena ), white-beaked dolphins ( Lagenorhynchus albirostris ), common minke whales ( Balaenoptera acutorostrata ), humpback whales ( Megaptera novaeangliae ), and blue whales ( Balaenoptera musculus ). Body size and condition were estimated for each species using unoccupied aerial vehicle photogrammetry. For baleen whales, seasonal energy storage was inferred from daily changes in body condition and expressed as blubber mass gain. Field metabolic rate was predicted from published allometric relationships. Energetic requirements were calculated using 10,000-iteration simulations incorporating parameter uncertainty, and were converted to prey biomass using published diet composition and prey energy density. Absolute energetic requirements and prey intake increased with body size, whereas mass-specific requirements declined. Harbour porpoises and white-beaked dolphins consumed the equivalent of 5.4% and 4.2% of their body mass per day, respectively, corresponding to ~ 20x and ~ 15x their body mass annually. In comparison, minke whales consumed 2.6% per day (~ 7x annually), humpback whales 1.3% (~ 4x) and blue whales 2.0% (~ 3x). Despite lower relative intake rates and lower abundance, large baleen whales accounted for 73.7% of total annual prey consumption in Icelandic waters; however, their combined consumption of commercially exploited fish species remained at ~ 40% of that of fisheries catches.\.