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

GK Silber,RR Reeves,DW Weller,TJ Moore,JD Adams

doi:10.3354/esr01093

Abstract

All species of large whales are susceptible to vessel strikes, 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 whalesEschrichtius robustusby vessels, by comparing patterns of whale distribution with the density of vessel traffic seasonally throughout the North Pacific 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, southbound migration, wintering, and northbound migration periods. Areas of apparently high risk were in the Russian Far East (Kamchatka peninsula and Okhotsk Sea), Bering Sea (including the Aleutian Islands), Gulf of Alaska, and along the entire west coast of North America. Risk appeared greatest during south- and northbound migration when much of the gray whale population is moving through waters near shore. Tanker, container, and bulk-carrier ships represent considerable risk to 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.

Highlights

All species of large whales are susceptible to being struck by vessels (Clapham et al 1999, Van Waerbeek et al 2007) and vessel strike is regarded as an important conservation concern for most of the populations that are recovering from commercial exploitation (Bettridge et al 2015, Monnahan et al.2015, Thomas et al 2016)
Vessel traffic was extensive throughout the entire North Pacific Ocean (NP) in 2019 (Fig. 1), as thousands of vessels made tens of thousands of trips
While our study focused on the risk of vessel strikes, areas of high vessel-strike risk indicate where gray whales are most exposed to elevated underwater noise from vessels

Summary

Introduction

All species of large whales are susceptible to being struck by vessels (Clapham et al 1999, Van Waerbeek et al 2007) and vessel (or ship) strike is regarded as an important conservation concern for most of the populations that are recovering from commercial exploitation (Bettridge et al 2015, Monnahan et al.2015, Thomas et al 2016). Ship-strike risk has been modeled for each of these species (except gray whales) in specific portions of the NP (e.g. Williams & O’Hara 2010, Redfern et al 2013), but in all cases, the range-wide effects of vessel-strike mortality (and morbidity) on abundance and population growth are uncertain. In April 2020, the Red Data Book of the Russian Federation listed the ‘Okhotsk Sea population of the gray whale’ as critically endangered (Reeves et al 2020).

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Discussion

Conclusion