The density of odontocete integument depends on blubber lipid composition and temperature

Abstract

Cetacean integument serves many functional roles, including contribution to whole body buoyancy. The blubber of the integument of different cetacean species contains varying concentrations of triacylglycerols (TAG) and wax esters (WE); generally, these lipid classes have different densities. Integument can also experience a wide range of temperatures during a dive, so its density may change with depth. The goals of this study were to measure integument density and isolated blubber lipid density in three deep‐diving odontocete species (n = 3–4)—short‐finned pilot whales (Globicephala macrorhynchus), pygmy sperm whales (Kogia breviceps), and Gervais' beaked whales (Mesoplodon europeaus)—at different temperatures (6°C–35°C), and to relate these densities to lipid content and composition. Kogia and Mesoplodon integument and isolated lipids had high WE content (78.7–99.5 wt%) and were less dense (by 1.7%–9.3%) than those of Globicephala, which were composed predominately of TAG. Generally, densities increased as temperature decreased. Changes in integument densities mirrored those of isolated lipid densities, suggesting that blubber lipids are largely responsible for the buoyant properties of cetacean integument. These data demonstrate that the contribution of the integument to whole body density depends on lipid class and temperature, and therefore may provide useful, species‐specific correction factors for diving energetics models.

Estimating body mass of sperm whales from aerial photographs

“…Model 3 . The relative weight proportions of each tissue type (blubber, muscle, bones, viscera) were used in combination with tissue‐specific densities (grams per millileter) to calculate the mean relative tissue density, D relative (Charrondiere et al, 2012; Lockyer, 1976; Lonati et al, 2019). Based on these proportions and the gas correction factor, the mean relative total tissue density, D relative , was calculated to be 886.7 kg/m 3 , and the predicted body mass of the free‐ranging sperm whales varied from 521 to 21,604 kg ( M = 7,929, SD = 5,014; Table S5, Figure 6C).…”

“…Using a published weight‐length relationship (Lockyer, 1976) adjusted for 25% fluid loss (Rice, 1989), Miller et al (2004b) were then able to predict the weight of the tagged whales, and ultimately, estimate the mean tissue density using data from animal‐borne tags: For the third approach (Model 3), we assumed a nonhomogenous body composition, as the body consists of several tissue types (blubber, muscle, bones, viscera). To account for these variations, we obtained the average body density of sperm whales, D relative , using the relative proportions of each tissue type, combined with tissue‐specific weights (Lockyer, 1976) and published tissue densities (grams per milliliter; Charrondiere et al, 2012; Lonati et al, 2019): (1) blubber accounts for 33% of body weight with a density of 0.87 g/ml (Lonati et al, 2019); (2) muscle accounts for 34% of body weight with a density of 0.96 g/ml; (3) bones account for 10% of body weight with a density of 0.72 g/ml; (4) visceral and organ tissue accounts for 9% of body weight with a density of 0.93 g/ml; and fluids comprise the remaining 14% of body weight with a density of 1.00 g/ml. The tissue density estimate from this approach was also adjusted to include gas components, similar to Model 2: For the fourth approach (Model 4) we modeled the estimated total body density (tissue and gas) of the three caught whales as a function of body volume (Lockyer, 1991) to examine the effect of body size on body density, and obtained a volume‐specific body density estimate, where D i ,estimated is the density of whale i for a given body volume: …”

“…(1) blubber accounts for 33% of body weight with a density of 0.87 g/ml (Lonati et al, 2019); (2) muscle accounts for 34% of body weight with a density of 0.96 g/ml;…”

“…For the third approach (Model 3), we assumed a nonhomogenous body composition, as the body consists of several tissue types (blubber, muscle, bones, viscera). To account for these variations, we obtained the average body density of sperm whales, D relative , using the relative proportions of each tissue type, combined with tissue-specific weights (Lockyer, 1976) and published tissue densities (grams per milliliter; Charrondiere et al, 2012;Lonati et al, 2019):…”

“…The data points represent the different reproductive classes (see color legend; 23 calves, 11 juveniles, 55 adults and 13 mothers). The solid black lines represent the predicted values from our study, where the measured body volume of free-ranging sperm whales (black points) was converted to body mass different body density values based on: (a) the mean density estimates from three caught whales (Lockyer, 1991); (b) the mean density estimate based on digital tags (Miller et al, 2004b); (c) the mean density estimated from relative tissue densities and proportions (Charrondiere et al, 2012;Lockyer, 1976Lockyer, , 1991Lonati et al, 2019); and (d) volume-specific body density estimates (Lockyer, 1991). The dashed red lines represent 95% confidence intervals.…”