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Vessel speed restrictions have three potentially beneficial effects on the risk of right whale ship strikes: a better chance for the whale to avoid the ship, a better chance for the crew to spot and avoid the whale, and less energy imparted to the whale in the event of a collision. We have developed a model of the first of these effects, using data from observed encounters of right whales with vessels and from whale diving activity. Using a probabilistic description of right whale response based on these observed behaviors, we estimate the likelihood of a strike given that the ship is initially on a collision course with the whale. Model results suggest that more than half of right whales located in or swimming into the path of an oncoming ship traveling at 15 knots or more are likely to be struck even when they do take evasive action. The model also suggests that the strike risk posed by a conventional ship moving at 20 to 25 knots can be reduced by 30 percent by slowing to 12 or 13 knots, and by 40 percent at 10 knots. Whales are likely to be largely safe from ship strike if they detect and react to an oncoming vessel at a distance of 250 m or more. Strike risk is considerable if the detection distance drops below 100 m