Metabolic cost of thermoregulation decreases after the molt in developing Weddell seal pups

Growth in marine mammals: a review of growth patterns, composition and energy investment

Growth of structural mass and energy reserves influences individual survival, reproductive success, population and species life history. Metrics of structural growth and energy storage of individuals are often used to assess population health and reproductive potential, which can inform conservation. However, the energetic costs of tissue deposition for structural growth and energy stores and their prioritization within bioenergetic budgets are poorly documented. This is particularly true across marine mammal species as resources are accumulated at sea, limiting the ability to measure energy allocation and prioritization. We reviewed the literature on marine mammal growth to summarize growth patterns, explore their tissue compositions, assess the energetic costs of depositing these tissues and explore the tradeoffs associated with growth. Generally, marine mammals exhibit logarithmic growth. This means that the energetic costs related to growth and tissue deposition are high for early postnatal animals, but small compared to the total energy budget as animals get older. Growth patterns can also change in response to resource availability, habitat and other energy demands, such that they can serve as an indicator of individual and population health. Composition of tissues remained consistent with respect to protein and water content across species; however, there was a high degree of variability in the lipid content of both muscle (0.1-74.3%) and blubber (0.4-97.9%) due to the use of lipids as energy storage. We found that relatively few well-studied species dominate the literature, leaving data gaps for entire taxa, such as beaked whales. The purpose of this review was to identify such gaps, to inform future research priorities and to improve our understanding of how marine mammals grow and the associated energetic costs.

Maintaining control: metabolism of molting Arctic seals in water and when hauled out

Seals haul out of water for extended periods during the annual molt, when they shed and regrow their pelage. This behavior is believed to limit heat loss to the environment given increased peripheral blood flow to support tissue regeneration. The degree to which time in water, particularly during the molt, may affect thermoregulatory costs is poorly understood. We measured the resting metabolism of three spotted seals (Phoca largha), one ringed seal (Pusa hispida) and one bearded seal (Erignathus barbatus) during and outside the molting period, while resting in water and when hauled out. Metabolic rates were elevated in spotted and ringed seals during molt, but comparable in water and air for individuals of all species, regardless of molt status. Our data indicate that elevated metabolism during molt primarily reflects the cost of tissue regeneration, while increased haul out behavior is driven by the need to maintain elevated skin temperatures to support tissue regeneration.

Using a combination of midazolam and butorphanol is a safe and effective reversible field sedation protocol for Weddell seal (Leptonychotes weddellii) pups

BACKGROUND

Weddell seals (Leptonychotes weddellii) are a well-studied species of phocid with an apparent sensitivity to immobilising agents. Mortality as high as 31% has been reported during field immobilisation. This study investigated the use of a benzodiazepine in combination with an opioid agonist/antagonist for sedation in Weddell seal pups as part of a physiological study.

METHODS

During the 2017 and 2019 Antarctic pupping seasons, 18 Weddell seal pups were sedated by intramuscular administration of a combination of midazolam and butorphanol or intravenous midazolam alone. Individuals were sedated at 1, 3, 5 and 7 weeks of age. Naltrexone and flumazenil were used to reverse sedation. The combination was 100% effective in providing appropriate sedation for the intended procedures.

RESULTS

Analyses were performed to investigate relationships between dose administered, age, individual reactions, adverse effects and changes in dive physiology. Transient apnoea (10-60 seconds) was the most frequently observed adverse effect. No sedation-associated morbidity or mortality occurred.

LIMITATIONS

The sample size is small and there is no pharmacokinetic information for either sedative or reversal in phocid species.

CONCLUSIONS

The combination of midazolam (0.2-0.3 mg/kg) and butorphanol (0.1-0.2 mg/kg) provided safe and effective sedation, with reversible effects, in Weddell seal pups.