Marine mammals are a common sight during the survey, and if they are present when we're setting up to fish, we hold operations until they leave the area. While preparing for a trawl in southern California, over 50 common dolphins (Delphinus) swam by the Bell M. Shimada, and their vocalizations were visible on the acoustic echograms. The acoustic image illustrates that the dolphin sounds were "heard" primarily by the 120 kHz, so they may have been primarily higher frequency "clicks" rather than lower frequency "whistles" (listen to common dolphin sounds).
Two common dolphins (Delphinus) seen off the Bell M. Shimada in southern California. Photo: Steve de Blois
Acoustic echogram, with horizontal x-axis showing time/distance for 38 kHz (top) and 120 kHz (bottom). Vertical y-axis shows water column from surface to bottom (shown as bright green line) with 2 additional bottoms (where signal bounces off surface, back down to bottom, and back up to surface) marked. Inferences from dolphin vocalization clicks appear as short vertical marks, primarily on the 120 kHz. Photo: NOAA Fisheries
