Body condition impacts blood and muscle oxygen storage capacity of free-living beluga whales (Delphinapterus leucas)

Abstract

Arctic marine ecosystems are currently undergoing rapid environmental changes. Over the past 20 years, individual growth rates of beluga whales (Delphinapterus leucas) have declined, which may be a response to climate change; however, the scarcity of physiological data makes it difficult to gauge the adaptive capacity and resilience of the species. We explored relationships between body condition and physiological parameters pertaining to oxygen (O 2 ) storage capacity in 77 beluga whales in the eastern Beaufort Sea. Muscle myoglobin concentrations averaged 77.9 mg g −1 , one of the highest values reported among mammals. Importantly, blood haematocrit, haemoglobin and muscle myoglobin concentrations correlated positively to indices of body condition, including maximum half-girth to length ratios. Thus, a whale with the lowest body condition index would have ∼27% lower blood (26.0 versus 35.7 ml kg −1 ) and 12% lower muscle (15.6 versus 17.7 ml kg −1 ) O 2 stores than a whale of equivalent mass with the highest body condition index; with the conservative assumption that underwater O 2 consumption rates are unaffected by body condition, this equates to a >3 min difference in maximal aerobic dive time between the two extremes (14.3 versus 17.4 min). Consequently, environmental changes that negatively impact body condition may hinder the ability of whales to reach preferred prey sources, evade predators and escape ice entrapments. The relationship between body condition and O 2 storage capacity may represent a vicious cycle, in which environmental changes resulting in decreased body condition impair foraging, leading to further reductions in condition through diminished prey acquisition and/or increased foraging efforts.

Year-Round Dive Characteristics of Male Beluga Whales From the Eastern Beaufort Sea Population Indicate Seasonal Shifts in Foraging Strategies

“…The aerobic dive limit (ADL) of adult belugas with a high body condition index is estimated at 17.4 min (Choy et al, 2019), which is close to the average dive durations of the two deepest dive classes reported here (Deep Benthic = 16.25 min and Deep Pelagic V = 17.25 min, Table 2). Deep Pelagic W dives were instead shorter than the belugas' ADL on average, and rarely exceeded this limit (median duration = 13.75 min, see Table 2).…”

Myoglobin Concentration and Oxygen Stores in Different Functional Muscle Groups from Three Small Cetacean Species

“…In marine mammals, the amount of muscle O 2 has traditionally been calculated by measuring the Mb concentration (g Mb • 100g −1 muscle) at a single location within a primary locomotor muscle and assuming a homogeneous distribution of Mb across all the body's muscles. Most previous studies have calculated total Mb from a single biopsy or muscle sample extrapolated to the locomotor muscle mass (epaxial group, hypaxial group and rectus abdominis) or the entire muscle mass, e.g., [13][14][15][16][17]. Nevertheless, several studies have shown significant differences in Mb concentration between muscles [18][19][20][21] and even within a single muscle [22][23][24] in marine mammals.…”

The immune response and diving: conservation considerations for belugas (Delphinapterus leucas) in a changing Arctic environment

“…Belugas are diving deeper and longer during foraging (Hauser 2016;Stafford et al 2016) and it is unknown if this will push animals-such as smaller belugas, which make shallower, shorter dives, with longer inter-dive intervals at the surface (Heide-Jørgensen et al 1998)-past their physiological limits. Reduced dive ability has also been linked to reduced O 2 stores in animals with poor body condition (Choy et al 2019). Poor nutrition affects both dive ability and immune function (e.g., Chandra 1999).…”

“…However, despite belugas' increased blood O 2 stores, Hedrick & Duffield (1991) report limited O 2 transport and conclude that belugas may be limited in their activity level (speed) during a dive. Belugas also possess increased capacity for muscle O 2 storage (myoglobin), muscle buffering capacity, red blood cell counts, haemoglobin and haematocrit, which have been reported to reach mature levels prior to weaning in belugas, which is faster than observed in other marine mammals (Noren & Suydam 2016;Noren et al 2018;Choy et al 2019).…”