Body density and diving gas volume of the northern bottlenose whale (Hyperoodon ampullatus).

Patrick Miller,Katsufumi Sato,Sophie Smout,Kagari Aoki,Saana Isojunno,Tomoko Narazaki

doi:10.1242/jeb.137349

Patrick Miller, Katsufumi Sato + Show 4 more

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https://doi.org/10.1242/jeb.137349

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Abstract

ABSTRACTDiving lung volume and tissue density, reflecting lipid store volume, are important physiological parameters that have only been estimated for a few breath-hold diving species. We fitted 12 northern bottlenose whales with data loggers that recorded depth, 3-axis acceleration and speed either with a fly-wheel or from change of depth corrected by pitch angle. We fitted measured values of the change in speed during 5 s descent and ascent glides to a hydrodynamic model of drag and buoyancy forces using a Bayesian estimation framework. The resulting estimate of diving gas volume was 27.4±4.2 (95% credible interval, CI) ml kg−1, closely matching the measured lung capacity of the species. Dive-by-dive variation in gas volume did not correlate with dive depth or duration. Estimated body densities of individuals ranged from 1028.4 to 1033.9 kg m−3 at the sea surface, indicating overall negative tissue buoyancy of this species in seawater. Body density estimates were highly precise with ±95% CI ranging from 0.1 to 0.4 kg m−3, which would equate to a precision of <0.5% of lipid content based upon extrapolation from the elephant seal. Six whales tagged near Jan Mayen (Norway, 71°N) had lower body density and were closer to neutral buoyancy than six whales tagged in the Gully (Nova Scotia, Canada, 44°N), a difference that was consistent with the amount of gliding observed during ascent versus descent phases in these animals. Implementation of this approach using longer-duration tags could be used to track longitudinal changes in body density and lipid store body condition of free-ranging cetaceans.

Highlights

Body condition is expected to affect and be affected by numerous aspects of the behavioral ecology of animals, including antipredator, foraging, migration and reproductive behavior (McNamara and Houston, 1990; Houston et al, 1993; Miller et al, 2012a; Crossin et al, 2014)
We describe how precisely body density can be estimated, how it is influenced by compression at the depths experienced by beaked whales, how it relates to gliding patterns during descent and ascent phases of dives, and some patterns of variability across individuals
In this study, we were able to effectively decompose the drag and buoyancy forces that operate on the beaked whale H. ampullatus body during gliding phases, enabling estimation of the speciestypical volume of gas carried from the surface and each animal’s tissue body density

Summary

Introduction

Body condition is expected to affect and be affected by numerous aspects of the behavioral ecology of animals, including antipredator, foraging, migration and reproductive behavior (McNamara and Houston, 1990; Houston et al, 1993; Miller et al, 2012a; Crossin et al, 2014). Recent research has indicated that beaked whales are sensitive to anthropogenic disturbance Measurement of body condition of beaked whales may be helpful as a research tool to quantify the risk that disturbance (from noise or other sources) or habitat changes could lead to a reduced ability of individuals to grow, reproduce or survive as a result of effects on their energy budget (NRC, 2005; New et al, 2013). Visual assessment of body condition appears to be effective for determining body condition of certain whale species (Bradford et al, 2012)

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