Lunge filter feeding biomechanics constrain rorqual foraging ecology across scale

Abstract

Fundamental scaling relationships influence the physiology of vital rates, which in turn shape the ecology and evolution of organisms. For diving mammals, benefits conferred by large body size include reduced transport costs and enhanced breath-holding capacity, thereby increasing overall foraging efficiency. Rorqual whales feed by engulfing a large mass of prey-laden water at high speed and filtering it through baleen plates. However, as engulfment capacity increases with body length (Engulfment Volume ∝ Body Length 3.57), the surface area of the baleen filter does not increase proportionally (Baleen Area ∝ Body Length1.82), and thus the filtration time of larger rorquals predictably increases as the baleen surface area must filter a disproportionally large amount of water. We predicted that filtration time should scale with body length to the power of 1.75 (Filter Time ∝ Body Length1.75). We tested this hypothesis on four rorqual species using multi-sensor tags with corresponding unoccupied aircraft systems (UAS) -based body length estimates. We found that filter time scales with body length to the power of 1.79 (95% CI: 1.61 - 1.97). This result highlights a scale-dependent trade-off between engulfment capacity and baleen area that creates a biomechanical constraint to foraging through increased filtration time. Consequently, larger whales must target high density prey patches commensurate to the gulp size to meet their increased energetic demands. If these optimal patches are absent, larger rorquals may experience reduced foraging efficiency compared to smaller whales if they do not match their engulfment capacity to the size of targeted prey aggregations.

Rorqual Lunge-Feeding Energetics Near and Away from the Kinematic Threshold of Optimal Efficiency

“…5 ), which turns out dominated by the duration of the water expulsion and prey retention stage ( T purge ; Goldbogen et al 2011 ; Guilpin et al 2019 , 2020 ; Kahane-Rapport et al 2020 ). Here, and intra-specifically ( Kahane-Rapport et al 2020 ), body size and swim speed appear as secondary factors in determining T lunge , as compared to other, environmentally and behaviorally driven factors ( Goldbogen et al 2013 ; Hazen et al 2015 ; Lesage et al 2017 ; Guilpin et al 2020 ). Thus, two tag-informed bounding values of the lunge duration are used instead in the upcoming expenditure scaling analysis.…”

“…This would go a long way in not only determining the efficiency on a lunge-to-lunge basis, but also in documenting the minimal patch densities that rorquals are known to avoid ( Hazen et al 2015 ). Patch geometry, along with dive depth, may also turn out as essential to the understanding of the duration of the purging/filtration stage ( Kahane-Rapport et al 2020 ), and by extension, lunge duration in relation to other expenditure metrics and environmental factors ( Goldbogen et al 2013 ; Hazen et al 2015 ; Lesage et al 2017 ).…”

Evidence for Size-Selective Predation by Antarctic Humpback Whales

“…Lunge feeding events-the rapid engulfment of a mouthful of prey-laden water followed by subsequent filtrationwere identified from the tag record (Figures 3A,B) via the identification of stereotyped maneuvers, typified by acceleration followed by rapid deceleration (Cade et al, 2016;Kahane-Rapport et al, 2020) as the whale is slowed from the engulfed water mass (Potvin et al, 2020). Tag ID mn200313-62, which only had a pressure sensor, was treated separately and lunge counts were estimated from the shape of the dive profile in combination with the vertical speed of the animal (similar to the method of Croll et al, 2001).…”

Biomechanically distinct filter-feeding behaviors distinguish sei whales as a functional intermediate and ecologically flexible species

“…1, photo C, and Fig. 3C), and the relatively short filtration times (Table 1; relative to Kahane-Rapport et al, 2020) further suggest that the buccal cavity was not fully inflated. Other planktonfeeding rorqual species lunge at faster speeds, open their mouth at the fastest point in their trajectory, stop fluking, and use their momentum to inflate their buccal pouch while foraging at depth (Cade et al, 2016) and near the surface (movie 1 from Segre et al, 2016;Torres et al, 2020, but kinematic data from surface lunges is limited).…”