SIDE-SCAN SONAR RECORDS AND DIVER OBSERVATIONS OF THE GRAY WHALE (ESCHRICHTIUS ROBUSTUS) FEEDING GROUNDS

¹ Moss Landing Marine Laboratories, Moss Landing, California 95039

Gray whales (Eschnichtius robustus) excavate infaunal invertebrates and sediment by suction, producing many large depressions in the sea floor. Diver observations indicate that side-scan sonar provides accurate estimates of the size of feeding excavations and the area of bottom covered by excavations (> 30% of the bottom). Although side scan does not detect some excavations because of small size (particularly < 3 m²) or their orientation with respect to the side-scan track, it gives a quantitative impression of the relative intensity of bottom disturbance by whales. This disturbance is directly related to habitat and prey utilization by whales.