Ontogenetic allometry and body composition of harbour porpoises (Phocoena phocoena, L.) from the western North Atlantic

Abstract

North Atlantic harbour porpoises Phocoena phocoena (L.) face considerable energetic challenges, as they are relatively small marine mammals with an intense reproductive schedule and a cold-water habitat. Postnatal growth of these porpoises was described using ontogenetic allometry and body composition techniques. The cross-sectional sample contained robust calves, immature, and mature porpoises (n = 122) incidentally killed in commercial ®shing operations between 1992 and 1998. Total mass and the mass of 26 body components were measured using a standard dissection protocol. Most body components grew similarly in female and male porpoises. Blubber, brain and skull were negatively allometric, while muscle and reproductive tissues exhibited positive allometry. Female heart, liver, intestine and mesenteric lymph node grew at signi®cantly higher rates than in males. Male locomotor muscle and pelvic bones grew signi®cantly faster than in females. High growth rates for visceral and reproductive organs in porpoises, relative to other mammals, may underlie their early maturation and support their intensive, annual reproductive schedule. Relative to other cetaceans, porpoises seem to allocate a larger percentage of their total body mass to blubber. This allocation to blubber, which is greatest in calves (37% of body mass), may provide harbour porpoises with the thermal insulation required to live in cold water. The factors in¯uencing growth rates and differential investments in body composition seem to change at various stages of a porpoise's life. Energy allocation in porpoises seems to shift from an emphasis on developing an insulative blubber layer in young animals to preparing the body for annual reproduction at sexual maturity.

Topographical variation in lipid content and morphological structure of the blubber in the striped dolphin

“…To minimize post-mortem degradation of blubber, only animals with a Smithsonian Institute code of 1 (live stranded and died naturally or by euthanasia) or 2 (fresh dead) (Geraci and Lounsbury 1993) were considered. Dolphins showed a normal to robust body condition, according to Cox et al (1998) and McLellan et al (2002) (Table 1). Blubber samples, including the entire thickness, were excised from a total of 11 body positions from each individual: four dorsal positions (1, 3, 6 and 9), three lateral positions (4, 7 and 10), and four ventral positions (2, 5, 8 and 11), as shown in Figure 1.…”

Seasonal and Ontogenetic Variation in Subcutaneous Adipose Of the Bowhead Whale (Balaena mysticetus)

“…Composed primarily of low-melting temperature unsaturated fatty acids, cetacean blubber is an effective, lowmaintenance insulator in cold water and may be so effective that bowheads have specialized organs that cool them down (K€ akel€ a and Hyv€ arinen, 1996;Pabst, 1996;Iverson, 2002;Dunkin et al, 2005;Ford, 2013). Biomechanically, blubber reduces energetic costs of locomotion via streamlining cetacean baupl€ ane and contributing to the maintenance of buoyancy (Pabst, 1996;Dearolf et al, 2000;Iverson, 2002;Kipps et al, 2002;McLellan et al, 2002).…”

Approaches for assessing the presence and impact of thyroid hormone disrupting chemicals in delphinid cetaceans

“…Blubber is dynamic and multifunctional, serving many roles: it functions biomechanically to provide support during locomotion and increases efficiency by streamlining the body surface (Hamilton et al, 2004;Pabst, 2000); it contributes to buoyancy (Dearolf et al, 2000;Kipps et al, 2002;McLellan et al, 2002); it is a primary site for lipid storage, which the animal utilizes during periods of energetic stress Koopman et al, 1996;Koopman et al, 2002;Struntz et al, 2004). The high lipid content also provides insulation, decreasing the heat loss from the body core to the external environment (Dunkin et al, 2005;Worthy and Edwards, 1990).…”

“…It has been hypothesized that adults display significantly lower total blubber lipid content, smaller adipocyte areas, higher structural fiber areas, and lower adipocyte numbers compared to subadults because as the dolphin's surface-area-to-volume ratio decreases with growth, there is less demand for insulation but greater demand for energy to support growth (Dunkin et al, 2005;McLellan et al, 2002;Struntz et al, 2004).…”

“…One possible explanation is that as the dolphin's surface-area-to-volume ratio decreases with growth, there is less demand for insulation but greater demand for energy to support growth (Dunkin et al, 2005;McLellan et al, 2002;Struntz et al, 2004). Furthermore, both male and female adults expend energy for reproduction, and this may decrease the lipid content of blubber and mobilize AHR agonists, inducing CYP1A1.…”