Vessel Collisions With Whales: The Probability of Lethal Injury Based on Vessel Speed

Abstract

Historical records demonstrate that the most numerous, per capita, ocean‐going‐vessel strikes recorded among large‐whale species accrue to the North Atlantic right whale (Eubalaena glacialis). As vessel speed restrictions are being considered to reduce the likelihood and severity of vessel collisions with right whales, we present an analysis of the published historical records of vessels striking large whales. We examine the influence of vessel speed in contributing to either a lethal injury (defined as killed or severely injured) or a nonlethal injury (defined as minor or no apparent injury) to a large whale when struck. A logistic regression model fitted to the observations, and consistent with a bootstrap model, demonstrates that the greatest rate of change in the probability of a lethal injury (Plethal) to a large whale occurs between vessel speeds of 8.6 and 15 knots where Plethal increases from 0.21 to 0.79. The probability of a lethal injury drops below 0.5 at 11.8 knots. Above 15 knots, Plethal asymptotically approaches 1. The uncertainties in the logistic regression estimates are relatively large at relatively low speeds (e.g., at 8 knots the probability is 0.17 with a 95% CI of 0.03–0.6). The results we provide can be used to assess the utility of vessel speed limits that are being considered to reduce the lethality of vessels striking the critically endangered North Atlantic right whale and other large whales that are frequent victims of vessel strikes.

Vessel collisions with small cetaceans worldwide and with large whales in the Southern Hemisphere, an initial assessment

“…A model fitted to around 100 observations where vessel speed and the fate of the whale was known suggests that at vessel speeds above 15 knots almost all collisions are likely to be lethal (Vanderlaan and Taggart, 2006). Multiple, complete and comminuted fractures of postcranial and cranial bones are common.…”

Predicting the acoustic exposure of humpback whales from cruise and tour vessel noise in Glacier Bay, Alaska, under different management strategies

“…The effect of adding a second ship was greatly reduced by having the ships travel at a slower speeds, as illustrated by the lower median values of MSPL and CSEL for simulations with 2 slow cruise ships compared to those with a single fast cruise ship. Available information also indicates that a benefit of reducing vessel speed is a lower probability of whale mortalities from ship strikes (Laist et al 2001, Vanderlaan & Taggart 2007. Most, if not all, marine protected areas with concerns about baleen whales could thus experience a twofold benefit from lower ship speeds.…”

“…Temporary or permanent hearing loss is theoretically possible in cases of extreme or chronic exposure to loud noises, but is not expected in these conditions. Substantial evidence indicates that vessel speed is an important factor affecting the likelihood and lethality of ship strikes (Laist et al 2001, Jensen & Silber 2003, Vanderlaan & Taggart 2007. Therefore, managers sometimes rely on vessel speed limits to mitigate the risks of ship strikes.…”

Harbour seals (Phoca vitulina) around an operational tidal turbine in Strangford Narrows: No barrier effect but small changes in transit behaviour

“…For this study, the turbine was considered to be on at times when either rotor was turning at or above 5 rpm. This threshold equates to a tip speed of 4 m s −1 , which is the lower end of the range of speeds considered to produce a significant risk of mortality to large cetaceans during collisions with ships (Vanderlaan & Taggart, 2007). A binary variable (turbine on or off) was defined from 5 minute averages of rotor speeds.…”