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Journal of Experimental Biology partnership with Dryad

SUMMARY

Lunge feeding by rorqual whales (Balaenopteridae) is associated with a high energetic cost that decreases diving capacity, thereby limiting access to dense prey patches at depth. Despite this cost, rorquals exhibit high rates of lipid deposition and extremely large maximum body size. To address this paradox, we integrated kinematic data from digital tags with unsteady hydrodynamic models to estimate the energy budget for lunges and foraging dives of blue whales (Balaenoptera musculus), the largest rorqual and living mammal. Our analysis suggests that, despite the large amount of mechanical work required to lunge feed, a large amount of prey and, therefore, energy is obtained during engulfment. Furthermore, we suggest that foraging efficiency for blue whales is significantly higher than for other marine mammals by nearly an order of magnitude, but only if lunges target extremely high densities of krill. The high predicted efficiency is attributed to the enhanced engulfment capacity, rapid filter rate and low mass-specific metabolic rate associated with large body size in blue whales. These results highlight the importance of high prey density, regardless of prey patch depth, for efficient bulk filter feeding in baleen whales and may explain some diel changes in foraging behavior in rorqual whales.

FOOTNOTES

  • Funding was provided by the United States Navy (SERDP Robert Holst, CNO-N45 Frank Stone, ONR Bob Gisiner) and NSERC to R.E.S. We thank J. A. Hildebrand for financial and logistical support related to the digital tags and tagging operations. J.A.G. was supported by the Scripps Institution of Oceanography Postdoctoral Fellowship Program. N.D.P. is supported by funds from the University of California Museum of Paleontology Remington Kellogg Fund, an NSF Graduate Research Fellowship, an NSERC Postdoctoral Research Fellowship and the Smithsonian Institution. We thank Donald Croll and Kelly Newton for providing the hydroacoustic prey map used in Fig. 2.

  • LIST OF ABBREVIATIONS

    Abody
    cross-section area of the body (closed-mouth, empty-cavity configuration)
    ac
    acceleration of an empty whale
    Ac
    instantaneous (vertical) cross-section mouth area
    afluke
    fluking acceleration
    Amouth
    mouth area
    AMR
    active metabolic rate
    aw
    acceleration of engulfed water
    BLFM
    basic lunge-feeding model
    BMR
    basal metabolic rate
    d
    travel distance
    EK
    kinetic energy
    FB
    buoyancy
    FBC
    buccal cavity wall force
    FED
    engulfment drag force
    Fext
    whale's weight minus buoyancy, projected along the direction of motion
    FMR
    field metabolic rate
    FSD
    shape drag force
    Fww
    water-to-water drag force
    kclose
    reaction constant used in Eqn A7 to calculate the cavity wall force during mouth closing
    kopen
    reaction constant used in Eqn A7 to calculate the cavity wall force during mouth opening
    L0
    length of the VGB (from the anterior end of the mandible to the umbilicus)
    Lbody
    body length
    Ljaw
    length of the jaw
    Mbody
    body mass
    Mc
    mass of an empty whale
    Mw
    mass of engulfed water
    Pdrag
    Energy loss
    Qdrag
    whale drag energy
    t
    time
    T
    fluking thrust
    TADL
    theoretical aerobic dive limit
    TE
    engulfment fluking thrust
    tengulf
    engulfment time
    TMJ
    temporomandibular joint
    TPE
    pre-engulfment fluking thrust
    Vc
    whale speed
    VGB
    ventral groove blubber
    Vw
    engulfed water speed
    W
    whale weight
    Γ
    proportionality constant used in Eqn A8, ∼6/5
    θgape
    gape angle
    ρw
    density of seawater
    φglide
    glide angle during descent
    ψ
    proportionality constant used in Eqn A3, =4/3
    ωhead
    width of the head
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