Literature Review of Ship Strike Risk to Whales
William D. Halliday
Large whales are at risk of being struck by ships, which at a minimum can lead to injury, but can also cause death. Given that many species of large whales have low populations and are considered of conservation concern, mortality from ship strikes can have devastating consequences for these species. In this literature review, we address three themes in the scientific literature regarding whales and ship strikes: 1) estimates of the frequency that whales are struck by ships; 2) calculations of the risk and lethality of ship strikes to whales; and 3) modeling the risk of ship strikes to whales based on ship tracking data and whale data. Many studies have quantified the number of whales being struck and killed by ships, typically using whale strandings databases from a region. Fin whales are often the most commonly struck whale in the records, although right whales are typically struck often. There is a positive, linear relationship between ship speed and the probability of a whale being struck, and a logistic relationship between ship speed and the probability of a ship strike killing a whale. According to one study, ships traveling at 11.8 knots have a 50% probability of a strike being lethal, increasing to 80% at 15.3 knots. These probability relationships can then be used to model ship strike risk in different regions with appropriate data on ship traffic and whale distribution, typically obtained through automatic identification system (AIS) ship track data and through whale telemetry or aerial surveys. Overlap between whales and ships is estimated by overlaying ship density with whale density, and risk of a lethal collision is then modeled by applying the logistic relationship between ship speed and probability of mortality. At least one study verified this modeling approach by examining spatial patterns from the strandings databases, and found a good match between their ship strike risk model outputs and the strandings of whales down to the species level. Overall, current methodology in assessing ship strike risk is robust, following a few assumptions, and can easily applied to different systems where the appropriate data are available.
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Halliday, W.D. (2020). Literature Review of Ship Strike Risk to Whales. Report written for Fisheries and Oceans Canada. Toronto, Canada: Wildlife Conservation Society, Canada, 1-11.