Increases in foraging performance of humpback whales in multi-predator feeding aggregations with California sea lions.

Marine predators frequently form ephemeral multi-predator feeding aggregations around dense prey patches, yet the mechanisms and outcomes of these dynamic events remain poorly resolved. We quantified how California sea lion (Zalophus californianus) presence influenced humpback whale (Megaptera novaeangliae) foraging using 46 multi-sensor video tags (mean duration: 7.4 ± 7.1 h) deployed on fish-feeding whales in Monterey Bay, California, USA (2014-2023). Across 1808 lunge-feeding events, whales foraging with sea lions exhibited a 23% higher feeding rate and a 16% shorter inter-lunge interval, while the overall percentage of time spent foraging did not change. Across deployments, humpback whale lunge speeds, manoeuvring metrics, and energetic proxies (overall dynamic body acceleration) did not differ with sea lion presence, indicating no detectable increase in per-lunge locomotor cost. When body size was accounted for in a lunge-level linear mixed-effects analysis, sea lion presence was associated with a 35% reduction in approach duration, an 8% increase in approach mean speed and a 25% shorter total lunge duration. Collectively, these results support the interpretation that sea lion-associated bait ball foraging increases humpback whale feeding frequency primarily by compressing search and approach time rather than altering engulfment mechanics or increasing per-lunge energetic expenditure, indicating a potential contribution of sea lions to prey concentration. This article is part of the theme issue 'Multi-predator feeding aggregations in the pelagic waters'.