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

SEASONAL VARIATION OF BLOOD ANALYTES ASSOCIATED WITH SKIN HEALTH IN ALASKAN ICE SEALS

Recent unusual mortality events involving skin pathology in bearded (Erignathus barbatus), ringed (Pusa hispida), and spotted seals (Phoca largha) in Alaska highlight the potential sensitivity of ice-associated species to the complex effects of climate change. The regulation of thyroid hormones, cortisol, and vitamin A have been shown to play essential roles in skin health and seasonal molt in some pinnipeds. Unfortunately, the lack of available reference data for healthy Alaskan ice seals has prevented the adequate evaluation of these factors in cases associated with mortality events. To improve understanding of blood analytes that may serve as useful markers of skin health, we compiled diagnostic information for individuals in long-term managed care following short-term rehabilitation. Thyroid hormones (TT4, TT3, and FT4d), cortisol, and vitamin A levels are reported for four ringed seals, four spotted seals, and three bearded seals at the Alaska SeaLife Center in Seward, Alaska, with serial samples obtained when possible and referenced to time of year. For ringed and spotted seals, the thyroid hormones and vitamin A showed a strong seasonal pattern with peak values obtained during the annual molt in spring, whereas cortisol values did not vary predictably between molting and non-molting periods. Trends were similar for individuals across both sex and species. Bearded seals had fewer available data for younger individuals only, but observed analyte values are provided for this understudied species. Collectively, these measurements can be used to support veterinary management of ice seals under human care and to provide initial baselines for skin health monitoring in wild populations and in stranded individuals with known skin lesions or pathology.

Breaking the fast: first report of dives and ingestion events in molting southern elephant seals

Southern elephant seals (SES) experience a 'catastrophic molt', a costly event characterized by the renewal of both hair and epidermis that requires high peripheral vascular circulation. Molting animals are therefore constrained by high metabolic heat loss and are thought to fast and remain on land. To examine the ability of individuals to balance the energetic constraints of molting on land we investigate the stomach temperature and movement patterns of molting female SES. We find that 79% of females swam and 61% ingested water or prey items, despite the cost of cold-water exposure while molting. This behavior was related to periods of warm and low wind conditions, and females that dived and ingested more often, lost less body mass. We conclude that the paradigm of fasting during the molt in this species, and the fitness consequences of this behavior should be reconsidered, especially in the context of a changing climate.

What are the Metabolic Rates of Marine Mammals and What Factors Impact this Value: A review

Over the past several decades, scientists have constructed bioenergetic models for marine mammals to assess potential population-level consequences following exposure to a disturbance, stressor, or environmental change, such as under the Population Consequences of Disturbance (pCOD) framework. The animal's metabolic rate (rate of energy expenditure) is a cornerstone for these models, yet the cryptic lifestyles of marine mammals, particularly cetaceans, have limited our ability to quantify basal (BMR) and field (FMR) metabolic rates using accepted 'gold standard' approaches (indirect calorimeter via oxygen consumption and doubly labeled water, respectively). Thus, alternate methods have been used to quantify marine mammal metabolic rates, such as extrapolating from known allometric relationships (e.g. Kleiber's mouse to elephant curve) and developing predictive relationships between energy expenditure and physiological or behavioral variables. To understand our current knowledge of marine mammal metabolic rates, we conducted a literature review (1900-2023) to quantify the magnitude and variation of metabolic rates across marine mammal groups. A compilation of data from studies using 'gold standard' methods revealed that BMR and FMR of different marine mammal species ranges from 0.2 to 3.6 and 1.1 to 6.1 x Kleiber, respectively. Mean BMR and FMR varied across taxa; for both measures odontocete levels were intermediate to higher values for otariids and lower values of phocids. Moreover, multiple intrinsic (e.g. age, sex, reproduction, molt, individual) and extrinsic (e.g. food availability, water temperature, season) factors, as well as individual behaviors (e.g. animal at water's surface or submerged, activity level, dive effort and at-sea behaviors) impact the magnitude of these rates. This review provides scientists and managers with a range of reliable metabolic rates for several marine mammal groups as well as an understanding of the factors that influence metabolism to improve the discernment for inputs into future bioenergetic models.