SUMMARY Rorqual baleen whales lunge feed by engulfment of tons of prey-laden water in a large and expandable buccal pouch. According to prior interpretations, feeding rorquals are brought to a near-halt at the end of each lunge by drag forces primarily generated by the open mouth. Accelerating the body from a standstill is energetically costly and is purported to be the key factor determining oxygen consumption in lunge-feeding rorquals, explaining the shorter dive times than expected given their sizes. Here, we use multi-sensor archival tags (DTAGs) sampling at high rates in a fine-scale kinematic study of lunge feeding to examine the sequence of events within lunges and how energy may be expended and conserved in the process of prey capture. Analysis of 479 lunges from five humpback whales reveals that the whales accelerate as they acquire prey, opening their gape in synchrony with strong fluke strokes. The high forward speed (mean depth rate: 2.0±0.32 m s−1) during engulfment serves both to corral active prey and to expand the ventral margin of the buccal pouch and so maximize the engulfed water volume. Deceleration begins after mouth opening when the pouch nears full expansion and momentum starts to be transferred to the engulfed water. Lunge-feeding humpback whales time fluke strokes throughout the lunge to impart momentum to the engulfed water mass and so avoid a near or complete stop, but instead continue to glide at ~1–1.5 m s−1 after the lunge has ended. Subsequent filtration and prey handling appear to take an average of 46 s and are performed in parallel with re-positioning for the next lunge.

The Greenland shark (Somniosus microcephalus), an iconic species of the Arctic Seas, grows slowly and reaches >500 centimeters (cm) in total length, suggesting a life span well beyond those of other vertebrates. Radiocarbon dating of eye lens nuclei from 28 female Greenland sharks (81 to 502 cm in total length) revealed a life span of at least 272 years. Only the smallest sharks (220 cm or less) showed signs of the radiocarbon bomb pulse, a time marker of the early 1960s. The age ranges of prebomb sharks (reported as midpoint and extent of the 95.4% probability range) revealed the age at sexual maturity to be at least 156 ± 22 years, and the largest animal (502 cm) to be 392 ± 120 years old. Our results show that the Greenland shark is the longest-lived vertebrate known, and they raise concerns about species conservation.

The largest animals are marine filter feeders, but the underlying mechanism of their large size remains unexplained. We measured feeding performance and prey quality to demonstrate how whale gigantism is driven by the interplay of prey abundance and harvesting mechanisms that increase prey capture rates and energy intake. The foraging efficiency of toothed whales that feed on single prey is constrained by the abundance of large prey, whereas filter-feeding baleen whales seasonally exploit vast swarms of small prey at high efficiencies. Given temporally and spatially aggregated prey, filter feeding provides an evolutionary pathway to extremes in body size that are not available to lineages that must feed on one prey at a time. Maximum size in filter feeders is likely constrained by prey availability across space and time.

Balaenid whales perform long breath-hold foraging dives despite a high drag from their ram filtration of zooplankton. To maximize the volume of prey acquired in a dive with limited oxygen supplies, balaenids must either filter feed only occasionally when prey density is particularly high, or they must swim at slow speeds while filtering to reduce drag and oxygen consumption. Using digital tags with three-axis accelerometers, we studied bowhead whales feeding off West Greenland and present here, to our knowledge, the first detailed data on the kinematics and swimming behaviour of a balaenid whale filter feeding at depth. Bowhead whales employ a continuous fluking gait throughout the bottom phase of foraging dives, moving at very slow speeds (less than 1 m s 21 ), allowing them to filter feed continuously at depth. Despite the slow speeds, the large mouth aperture provides a water filtration rate of approximately 3 m 3 s 21 , amounting to some 2000 tonnes of water and prey filtered per dive. We conclude that a food niche of dense, slow-moving zooplankton prey has led balaenids to evolve locomotor and filtering systems adapted to work against a high drag at swimming speeds of less than 0.07 body length s 21 using a continuous fluking gait very different from that of nekton-feeding, aquatic predators.