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Co-occurrence of gray whales and vessel traffic in the North Pacific Ocean

Gregory K. Silber*, David W. Weller, Randall. R. Reeves, Jeffery D. Adams, Thomas J. Moore

*Corresponding author:

ABSTRACT: All species of large whales are susceptible to being struck by vessels. Instances of vessel strikes of gray whales Eschrichtius robustus are reported every year but the true scale and geographical extent of such strikes is not known. This paper provides a qualitative assessment of the range-wide risks posed to gray whales by vessels by comparing patterns of whale distribution with the density of vessel traffic (displayed in grid cells as vessel hours of operation) seasonally throughout the North Pacific in 2019. Thousands of vessels made tens of thousands of trips in 2019. Areas of very high vessel density were evident year-round near many coastlines, along inter-continental trade routes, and at hubs of commercial shipping near port entrances. Gray whales were exposed to vessel strikes throughout their range and in their feeding, south-bound migration, wintering, and north-bound migration periods. Areas of apparently high risk were in the Russian Far East (along the Kamchatka Peninsula and in the Okhotsk Sea), Bering Sea (including near the Aleutian Islands), Gulf of Alaska and along the entire west coast of North America. Risk appeared greatest during south- and north-bound migration when much of the gray whale population is moving through waters near shore. Tanker, container and bulk-carrier ships represent considerable risk to gray whales (as well as some other large whales in the North Pacific Ocean), but the large geographical extent of commercial fishing activities suggests that fisheries are also a substantial source of risk. Vessel-strike risk maps indicate the relative extent of exposure of gray (and other) whales to underwater vessel noise. The number of gray whales killed by ship strikes each year may be in the tens, or perhaps the low hundreds. Additional analyses, including quantitative assessments, are warranted to further clarify the risk of vessel strikes to gray whales.