Confronting the challenges of whale avoidance by large vessels to reduce collision risk: A quantitative approach

Abstract

Disturbance of wildlife by human transportation infrastructure is ubiquitous. This type of human-wildlife conflict has the potential to negatively impact wildlife population growth rates, especially for at-risk species like large whales. While many whale populations are rebounding as a result of a moratorium on commercial whaling, increasing ship traffic constitutes a significant threat to whale conservation efforts in the form of ship-whale collisions (“ship strikes”). Ship strike avoidance is difficult because vessel operators can only see whales when they are breaking the surface of the water, or “available for detection,” and even then, they will only see them a fraction of the time (the “perception process”). We investigated the ability of ship operators to detect and actively avoid whales by quantifying two processes: the ability of vessel operators to ascertain the direction of travel of whales (Chapter 2), and the varying detection challenges faced by vessel operators as whales move through the “strike zone” (Chapter 3). In Chapter 2, we modeled the ability of vessel operators to congruously determine whale direction of travel as a function of ship-to-whale distance and the number of surfacings in a bout. We found that the probability of making a congruous DT assignment increased as surfacing bout length increased and as ship-to-whale distance decreased. We also modeled the time it took vessel operators to make a DT assignment after the first sighting of a whale, and found that the probability of making a DT assignment was around 0.5 after three minutes had passed. In Chapter 3, we modeled the probabilities of whales entering and exiting the upper portion of the water column where they are at risk of ship strike (the “strike zone”), as well as the availability probability. We found that whales are present and undetected in the strike zone far more frequently than they are available for detection, which has important consequences for ship strike avoidance protocols and regulations