MYOGLOBIN SATURATION IN FREE-DIVING WEDDELL SEALS

Although the consumption of myoglobin-bound O-2 (MbO(2)) stores in sea l muscles has been demonstrated in seal muscles during laboratory simu lations of diving, this may not be a feature of normal field diving in which measurements of heart rate and lactate production show marked d ifferences from the profound diving response induced by forced immersi on. To evaluate the consumption of muscle MbO(2) stores during unrestr ained diving, we developed a submersible dual-wavelength laser near-in frared spectrophotometer capable of measuring MbO(2) saturation in swi mming muscle. The probe was implanted on the surface of the latissimus dorsi of five subadult male Weddell seals (Leptonychotes weddelli) re leased into a captive breathing hole near Ross Island, Antarctica. Fou r seals had a monotonic decline of muscle O-2 saturation during free d iving to depths up to 300 m with median slopes of -5.12 +/- 4.37 and - 2.54 +/- 1.95%/min for dives lasting <17 and >17 min, respectively. Th ere was no correlation between the power consumed by swimming and the desaturation rate. Two seals had occasional partial muscle resaturatio ns late in dives, indicating transfer of Oz from circulating blood to muscle myoglobin. Weddell seals partially consume their MbO(2) stores during unrestrained free diving.