Abstract Seabirds cue into other birds and marine mammals to amplify their foraging success. Consequently, changes to the community (e.g. as the climate warms) can impact foraging success and potentially fitness. For example, flying birds that use groups of seals or penguins as cues might decline if the seal or penguin population declines, owing to fewer opportunities for positive foraging associations with one another. To test this idea, we leveraged data from transect surveys spanning 38 years (data collected in 1985, 1991, 1993 and 2023) in waters surrounding the subantarctic island South Georgia. We asked: ‘Has the frequency with which seabirds form statistically significant pairings with other species declined over time?’ We found such changes have occurred: network connectivity (the percentage of species pairings out of all possible pairs) decreased from approximately 40 to 7%, although the overall impact of warming on the community in 2023 was complicated by the arrival of a 100 km iceberg from the Weddell Sea. Possible fitness impacts from reduced associations could have broad-ranging consequences as the ocean continues to warm and the community changes. The results presented here represent one of just a handful of at-sea surveys documenting the winter seabird community at South Georgia. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.
Abstract 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 pelagic waters’.
Abstract Multi-predatory feeding aggregations (MPFAs) occur when several predator species concurrently exploit shared, spatially and temporally aggregated prey. Although MPFAs are well described in some marine ecosystems, their prevalence in the Norwegian Sea has historically been underestimated. Here, we synthesize existing biological, acoustic, visual and behavioural evidence to reinterpret classical predator–prey observations through the lens of MPFAs. Our reassessment revealed that numerous events previously described as single-predator interactions actually represent multi-species feeding assemblages involving marine mammals, large predatory fishes and seabirds. These MPFAs primarily target highly abundant pelagic schooling fishes, such as Norwegian spring-spawning herring, northeast Atlantic (NEA) mackerel, blue whiting and capelin. We compiled, to our knowledge, the first region-wide overview of documented and inferred MPFAs in the Norwegian Sea, characterizing species assemblages, ecological settings and behavioural mechanisms. We further discussed how predator physiology, group foraging strategies, prey schooling dynamics and oceanographic features interact to create conditions favourable for MPFAs. Recognizing MPFAs as common and ecologically influential phenomena has important implications for understanding food webs and ecosystem-based fisheries management. Therefore, we recommend that future research in the region explicitly incorporate MPFAs through multi-sensor observational approaches, behavioural analyses and integration into ecosystem models to better represent the functional role of predators in the NEA. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.
Abstract Multi-predator feeding aggregations (MPFAs) are ocean events whereby two or more species forage on the same or co-occurring prey. Such communities are dynamic, with community structure reflecting the connections between species and the benefits and costs of associations. The analysis of MPFAs provides an overview of ecosystem health, with social networks reflecting prey and available resources. Demographic analyses of MPFAs can act as process-based indicators of community responses to rapid change. To understand complex community dynamics, we identified community types in MPFAs using hierarchical clustering and determined the social associations and roles of the different species present. We collected data on 179 MPFA events, recording 55.4 hours of behavioural observations from 33 843 individuals belonging to 19 seabird and three cetacean species in the Hauraki Gulf, New Zealand. Eight MPFA community types were identified, representing planktivorous, scavenger or polytrophic aggregations. Seabird–cetacean and seabird–seabird associations dominated species associations. We interpret the species’ roles by combining our observations of behavioural states with knowledge from the literature. The study of marine MPFAs offers a community-level perspective for understanding community dynamics and food-web organization under future ecosystem changes. Using social network analyses, we advance the understanding of species interconnectedness to better inform ecosystem-based conservation management. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.
Abstract The formation of groups by prey is one of the most widespread evolutionary responses to predation. However, while the anti-predation benefits provided to prey within groups have been extensively explored in the literature, the subsequent response of predators to grouping behaviour has lacked attention. In particular, what strategies predators use to attack grouping prey, and whether predation strategies have evolved to explicitly exploit the behaviour of prey groups, remains underexplored. In this review, we discuss the behavioural strategies predators have evolved to counteract the collective defences of prey groups, and in some cases capitalize on the prey's grouping behaviour. Specifically, we focus on the different strategies predators use to break apart and disrupt groups, while also exploring how predators capitalize on cohesion and coordinated movement to increase the likelihood of a successful attack. Overall, this review challenges the assumption that grouping is universally advantageous for prey, showing that predators have evolved a variety of successful strategies to overcome, and even exploit, grouping prey. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.
