Swimming velocities, breathing patterns, and estimated costs of locomotion in migrating gray whales, Eschrichtius robustus

Abstract

This study was conducted to determine the swimming velocities and breathing patterns of south-migrating gray whales (Eschrichtius robustus) and to estimate their minimum costs of transport during migration. Swimming velocities and breathing patterns were monitored with theodolite techniques from a coastal vantage point on Point Loma, San Diego County, CA. Estimates of energy expenditures were based on observed breathing rates and on extrapolations of tidal lung volume and oxygen uptake measurements made on unrestrained and on captive gray whales. The results of 74 whales monitored over 354 whale∙km yielded mean velocities of 2.0 m∙s⁻¹ and mean breathing rates of 0.72 breaths∙min⁻¹. The regression of breathing rates on swimming velocities (V) by the method of least squares is best described by the equation, breathing rate = 0.5 + 0.024 V^3.0. The calculated minimum cost of transport for a 12-m, 15-t whale was 0.046 W∙s∙N⁻¹∙m⁻¹ at the observed mean swimming velocity of 2 m∙s⁻¹ during the southward migration. The coefficient of total drag was estimated to be 0.06. Rates of lipid depletion approximate 6% of body weight per month if no supplementary food intake occurs for the 4- to 6-month period each year that gray whales are presumed to fast.