Body oxygen stores, aerobic dive limits, and the diving abilities of juvenile and adult muskrats (Ondatra zibethicus)

Intraspecific variability in body oxygen reserves, muscle buffering capacit y, diving metabolic rate, and diving behavior were examined in recently cap tured juvenile and adult muskrats. Allometric scaling exponents for lung (b =1.04), blood (b=0.91), and total body oxygen storage capacity (b=1.09) did not differ from unity. The concentration of skeletal muscle myoglobin scal ed positively with mass in 254-600-g juveniles (b=1.63) but was mass-indepe ndent in larger individuals. Scaling exponents for diving metabolic rate an d calculated aerobic dive limit (ADL) were 0.74 and 0.37, respectively. Con trary to allometric predictions, we found no evidence that the diving abili ties of muskrats increased with age or body size. Juveniles aged 1-2 mo exh ibited similar dive times but dove more frequently than summer-caught adult s. Average and cumulative dive times and dive : surface ratios were highest for fall- and winter-caught muskrats. Total body oxygen reserves were grea test in winter, mainly due to an increase in blood oxygen storage capacity. The buffering capacity of the hind limb swimming muscles also was highest in winter-caught animals. Several behavioral indicators of dive performance , including average and maximum duration of voluntary dives, varied positiv ely with blood hemoglobin and muscle myoglobin concentration of muskrats. H owever, none of the behavioral measures were strongly correlated with the t otal body oxygen reserves or ADLs derived for these same individuals.