The harp seal, <i>Pagophilus groenlandicus</i> (Erxleben, 1777)

Abstract

Three types of fibre, dark (type 1), light (type 2) and intermediate, were distinguished in the caval sphincter muscle of the diaphragm in the harp seal (Pagophilus groenlandicus) using histochemical and electron-microscopic techniques. The dark fibre contained large peripheral aggregations of mitochondria, numerous lipid droplets and dense aggregates of glycogen granules. The same features were observed in the dark fibre of the diaphragm muscle too. In the light of the low oxidative enzyme activity and high lipase activity observed in the diaphragm and other skeletal muscles of the harp seal in previous studies, it is postulated that these mitochondrial aggregations and lipid droplets represent an adaptation for the generation of heat through non-shivering thermogenesis comparable to that in the brown adipose tissue. Such ability to generate and maintain heat by uncoupling the oxidative phosphorylation process should enable the caval sphincter muscle to function efficiently in regulating the cardiac return of blood from the inferior vena cava during a dive when the body temperature as a whole drops. The lack of the regional differences in the fibre composition of the harp seal diaphragm, as were reported in the rat diaphragm, is attributed to the seal’s large body size, lower metabolic rate and diving habit.

Extreme physiological adaptations as predictors of climate‐change sensitivity in the narwhal,Monodon monoceros

“…Based on histochemical and biochemical profiles, the major locomotory skeletal muscle of the narwhal, the longissimus dorsi, indicates an animal built for slow, endurance swimming. Mean fiber diameters for slow twitch fibers (62.6 ± 20.0) and fast twitch fibers combined (60.3 ± 16.2) were 19%-162% larger than that reported for the same muscle in harp seals (George and Ronald 1973), but were similar in size to the locomotory muscle (quadriceps) of humans (Dubowitz 1985). Although both fast twitch and slow twitch fibers were identified (Table 2, Fig.…”

Comparative Muscle Physiology of Ringed (Pusa hispida), Bearded (Erignathus barbatus), and Spotted (Phoca largha) Seals from the Bering and Chukchi Seas

“…Our findings suggest a potential pattern in fiber type proportions between the Phocinae and Monachinae subfamilies. Hooded and ribbon seals are now the only Phocinae seals for which comparable fiber type data remain unavailable, but species from this lineage typically have a predominance of fast-twitch fibers in locomotor muscles (George et al, 1971;Reed et al, 1994;Watson et al, 2003). This pattern is opposite to that exhibited by the few Monachinae species that have been measured (i.e., elephant and Weddell seals), which have primarily slow-twitch fibers (Kanatous et al, 2002(Kanatous et al, , 2008Moore et al, 2014).…”

“…The locomotor muscles of deep, long-duration divers like elephant (Mirounga angustirostris) and Weddell (Leptonychotes weddellii) seals are almost exclusively composed of slow-twitch fibers and have particularly high myoglobin content ([Mb]) (Kanatous et al, 2002(Kanatous et al, , 2008. In contrast, species with more moderate dive profiles, like generalist harbor seals (Phoca vitulina), have a more even mix of slow-and fast-twitch fibers and have relatively lower [Mb] in locomotor muscles (George et al, 1971;Reed et al, 1994;Watson et al, 2003). Although much is known about the muscle profiles of a few wellstudied pinniped species, there are many seal species for which data are limited or lacking altogether.…”

Acoustic Monitoring of Professionally Managed Marine Mammals for Health and Welfare Insights

“…Behavioral hearing tests have been successfully trained in bottlenose dolphins, (e.g., Tursiops sp. [ 55 ]; killer whales ( Orcinus orca, [ 56 , 57 ]); false killer whales ( Pseudorca crassidens, [ 58 ]); Pacific white-sided dolphins ( Lagenorhynchus obliquidens , [ 59 ]); Tucuxis ( Sotalia fluviatilis , [ 60 ]); harbor porpoises ( Phocoena phocoena, [ 61 ]); California sea lions ( Zalophus californianus, [ 62 , 63 ]); Stellar sea lions ( Eumetopias jubatus , [ 64 , 65 ]); harbor seals ( Phoca vitulina, [ 62 , 63 ]); Harp seals ( Pagophilus groenlandicus, [ 66 ]); spotted seals ( Phoca largha , [ 63 ]); ringed seals ( Pusa hispida , [ 67 ]); bearded seals ( Erignathus barbatus; [ 68 ]); northern elephant seals ( Mirounga angustirostris , [ 62 ]); northern fur seals ( Callorhinus ursinus , [ 69 ]); Hawaiian monk seals ( Neomonachus schauinslandi, [ 70 ]); Pacific walrus ( Odobenus rosmarus divergens , [ 71 ]); belugas ( Delphinapterus leucas , [ 72 ]); Florida manatees ( Trichechus manatus latirostris , [ 73 ]); polar bears ( Ursus maritimus , [ 74 ]); and sea otters ( Enhydra lutris , [ 75 ]). Behavioral hearing tests are the “gold-standard” of tests to determine individual animal sensitivity and range.…”