DIVING AND SWIMMING PERFORMANCE OF WHITE WHALES, DELPHINAPTERUS-LEUCAS - AN ASSESSMENT OF PLASMA LACTATE AND BLOOD-GAS LEVELS AND RESPIRATORY RATES

The white whale Delphinapterus leucas is an exceptional diver, yet we know little about the physiology that enables this species to make pro longed dives. We studied trained white whales with the specific goal o f assessing their diving and swimming performance. Two adult whales pe rformed dives to a test platform suspended at depths of 5-300 m. Behav ior was monitored for 457 dives with durations of 2.2-13.3 min. Descen t rates were generally less than 2 m s(-1) and ascent rates averaged 2 .2-3 m s(-1). Post-dive plasma lactate concentration increased to as m uch as 3.4 mmol l(-1) (4-5 times the resting level) after dives of 11 min. Mixed venous PO2 measured during voluntary breath-holds decreased from 79 to 20 mmHg within 10 min; however, maximum breath-hold durati on was 17 min. Swimming performance was examined by training the whale s to follow a boat at speeds of 1.4-4.2 m s(-1). Respiratory rates ran ged from 1.6 breaths min(-1) at rest to 5.5 breaths min(-1) during exe rcise and decreased with increasing swim speed. Postexercise plasma la ctate level increased to 1.8 mmol l(-1) (2-3 times the resting level) following 10 min exercise sessions at swimming speeds of 2.5-2.8 m s(- 1). The results of this study are consistent with the calculated aerob ic dive limit (O-2 store/metabolic rate) of 9-10 min. In addition, whi te whales are not well adapted for high-speed swimming compared with o ther small cetaceans.