Hierarchical foraging movement of humpback whales relative to the structure of their prey

Abstract

Movement within and between prey patches can influence the fitness of a predator, and understanding such foraging decisions is an important topic in ecology. Most research has found sustained foraging in dense prey patches but has focused on the movement of raptorial predators that feed on single prey items, or suspension-feeders foraging on comparatively immobile zooplankton. The goal of this study was to investigate the fine-scale movement of a suspension-feeding marine vertebrate species while foraging for mobile prey. Using animal-borne tags and surface observations, we analyzed the movement of foraging humpback whales Megaptera novaeangliae within and among acoustically detected patches of sand lance Ammodytes spp. in the water column in the southern Gulf of Maine, USA. Analyzing data from 9 whales tagged between 2008 and 2012, we found hierarchical whale foraging movements that paralleled a complex, hierarchically structured prey landscape. For 7 out of 9 whales, feeding bout scales corresponded to prey patch scales. For 6 out of 9 whales, movement between sequential feeding events was not significantly different from distances between neighboring prey schools. Targeting neighboring schools during sequential feeding events, as opposed to sustained foraging in profitable patches, may increase foraging success in marine suspension-feeders targeting mobile prey, which confirms findings from many other marine predator taxa feeding on mobile prey species. Our study presents novel evidence for the high behavioral plasticity of an intermittent suspensionfeeder targeting mobile prey, adapting its movement to the behavior of its prey and the structure of its prey field.

New views of humpback whale flow dynamics and oral morphology during prey engulfment

“…There are many humpback foraging behaviors that were not observed in our study. Nonetheless we have found-throughout all the sequences we analyzed, and relative to other published accounts of humpback feeding behavior (Jurasz and Jurasz 1979;Hain et al 1981;D'Vincent et al 1985;Hays et al 1985;Goldbogen et al 2008;Friedlaender et al 2009Friedlaender et al , 2013Hazen et al 2009;Ware et al 2010;Simon et al 2012;Kirchner et al 2018)-certain common aspects that appear to be largely or entirely invariant. These include high (>80 ) gape angle with a large contribution from cranial elevation, rapid (within 2 s) filling of the oral (ventral) pouch, and initial expulsion of excurrent water from the anterior-most baleen (unless the whale's head is raised at an angle above the water surface, when water pours out closer to the angle of the mouth).…”

“…; Kirchner et al . )—certain common aspects that appear to be largely or entirely invariant. These include high (>80°) gape angle with a large contribution from cranial elevation, rapid (within 2 s) filling of the oral (ventral) pouch, and initial expulsion of excurrent water from the anterior‐most baleen (unless the whale's head is raised at an angle above the water surface, when water pours out closer to the angle of the mouth).…”

“…The study of feeding in humpback whales and other mysticetes has been revolutionized by digital tagging , Goldbogen and Meir 2014, Kirchner et al 2018. Small, unobtrusive devices temporarily affixed to a whale's body by suction cups measure a whale's acceleration, depth, and body position/motion in various directions while cameras record close-up features.…”

“…Fortunately, just as digital tags have gained new capabilities while decreasing in size and cost (Goldbogen et al , 2017aGoldbogen and Meir 2014), other recent technological advances have made it easier to capture and analyze video recordings of marine mammal behavior (Nowacek et al 2001(Nowacek et al , 2016Anderson and Gaston 2013;Hunt et al 2013;Karnowski et al 2016;Pirotta et al 2017Pirotta et al , 2019Johnston 2019), and particularly of humpback whales (Ware et al 2006, Christiansen et al 2016a, Kirchner et al 2018. Simple, user-friendly, and inexpensive video cameras and editing software enable researchers to document feeding and other activities (Letessier et al 2015, Raoult et al 2016, Brooks 2017.…”

“…, Kirchner et al . ). Simple, user‐friendly, and inexpensive video cameras and editing software enable researchers to document feeding and other activities (Letessier et al .…”