How Baleen Whales Feed: The Biomechanics of Engulfment and Filtration

Abstract

Baleen whales are gigantic obligate filter feeders that exploit aggregations of small-bodied prey in littoral, epipelagic, and mesopelagic ecosystems. At the extreme of maximum body size observed among mammals, baleen whales exhibit a unique combination of high overall energetic demands and low mass-specific metabolic rates. As a result, most baleen whale species have evolved filter-feeding mechanisms and foraging strategies that take advantage of seasonally abundant yet patchily and ephemerally distributed prey resources. New methodologies consisting of multi-sensor tags, active acoustic prey mapping, and hydrodynamic modeling have revolutionized our ability to study the physiology and ecology of baleen whale feeding mechanisms. Here, we review the current state of the field by exploring several hypotheses that aim to explain how baleen whales feed. Despite significant advances, major questions remain about the processes that underlie these extreme feeding mechanisms, which enabled the evolution of the largest animals of all time.

A behavioural framework for the evolution of feeding in predatory aquatic mammals

“…Cetaceans with relatively short and inflexible necks use ram feeding to overtake and engulf prey (figure 2d), irrespective of whether the latter consists of an individual fish, as in the case of oceanic dolphins, or entire swarms/schools of krill, copepods and forage fish, as in most baleen whales [1]. Right whales and rorquals are both ram feeders, but differ in employing this behaviour in a continuous (also known as skim feeding) and intermittent (lunge, gulp or engulfment feeding) fashion, respectively [22,30,31].…”

“…These two types of filter may work in different ways, with at least some mysticetes (e.g. right whales) employing longitudinal cross-flow, rather than transverse throughput filtration [22,44].…”

Oral cavity hydrodynamics and drag production in Balaenid whale suspension feeding

“…In contrast, and again during filtration, the baleen of rorquals (Balaenopteridae) are exposed not to the open ocean (except momentarily, during engulfment) but to the intraoral water-prey mixture engulfed during a lunge and contained within the closed buccal cavity [11–13]. And so the movement of water past and out through baleen is instead enabled by internal pressure buildup within the buccal cavity, as caused by the contraction of musculature embedded within the ventral groove blubber (VGB) [14, 15].…”

Multiaxial movements at the minke whale temporomandibular joint

“…Rorquals include humpback ( Megaptera novaeangliae ), fin ( Balaenoptera physalus ), and blue whales ( Balaenoptera musculus ), the largest animals that have ever lived. During ram‐propelled lunge feeding on schooling zooplankton and fish (Figure ), the mouth opens wide to engulf enormous volumes (5–80+ m 3 ) of prey‐laden water (Goldbogen, ; Goldbogen et al, ; Lambertsen, ; Pivorunas, ; Potvin, Goldbogen, & Shadwick, ; Werth et al, ; Werth & Ito, ).…”

“…This elaborately outlined scheme of mandibular movements notwithstanding, the precise ways in which the distinct types of triaxial motion actually occur during basic gape change (Δ‐rotation) has been almost wholly unknown, even in the Lambertsen et al () account. However, based on our preliminary knowledge of rorqual mandibular motion, as concluded from (a) manipulation of numerous deceased specimens of different rorqual species (Figure ), (b) observation of gape in living whales (both in vivo and via videorecorded sequences), and (c) the limited published accounts of rorqual gape action (e.g., Arnold, Birtles, Sobtzick, Matthews, & Dunstan, ; Brodie, ; Cade, Friedlaender, Calambokidis, & Goldbogen, ; Goldbogen et al, ), we hypothesized that these three types of motion, along intersecting X, Y, and Z axes (Figure ), represent a complex system. Specifically, we define this complexity as having five discrete aspects.…”