Minke whale feeding rate limitations suggest constraints on the minimum body size for engulfment filtration feeding

Bulk filter feeding has enabled gigantism throughout evolutionary history. The largest animals, extant rorqual whales, utilize intermittent engulfment filtration feeding (lunge feeding), which increases in efficiency with body size, enabling their gigantism. The smallest extant rorquals (7-10 m minke whales), however, still exhibit short-term foraging efficiencies several times greater than smaller non-filter-feeding cetaceans, raising the question of why smaller animals do not utilize this foraging modality. We collected 437 h of bio-logging data from 23 Antarctic minke whales (Balaenoptera bonaerensis) to test the relationship of feeding rates (λ_f) to body size. Here, we show that while ultra-high nighttime λ_f (mean ± s.d.: 165 ± 40 lunges h^-1; max: 236 lunges h^-1; mean depth: 28 ± 46 m) were indistinguishable from predictions from observations of larger species, daytime λ_f (mean depth: 72 ± 72 m) were only 25-40% of predicted rates. Both λ_f were near the maxima allowed by calculated biomechanical, physiological and environmental constraints, but these temporal constraints meant that maximum λ_f was below the expected λ_f for animals smaller than ~5 m-the length of weaned minke whales. Our findings suggest that minimum size for specific filter-feeding body plans may relate broadly to temporal restrictions on filtration rate and have implications for the evolution of filter feeding.