Composition and Analysis of Vessel Speeds off the Coast of Washington State

Abstract

Most species of whales are vulnerable to vessel collisions, and the probability of lethality increases logistically with vessel speed. Spatially explicit risk assessments can inform the marine management process about the potential for vessel collisions. We used Satellite Automatic Identification Systems data from 2013 and 2014 to calculate vessel speed over ground around the Olympic Coast National Marine Sanctuary. Nearby shipping lanes connecting the Ports of Vancouver, Seattle, Tacoma, and Portland have the greatest density of vessel traffic, and these densely traveled routes continue outside the US Exclusive Economic Zone. We characterized speed and density based on vessel type and for areas of interest, including the Cetacean Density and Distribution Working Group’s Biologically Important Areas. Cargo and tanker vessels constitute the majority of distance traveled at the greatest speeds. We found that calculated speed is higher and less variable than broadcast speed for most vessel types. Temporal gaps in the SAIS data led to uncertainty in transit path and a resulting systematic underestimation of vessel speed. Calculating vessel speed is important so that risk to cetaceans from collisions is not underestimated by using broadcast speed in risk assessments.