A spatially explicit model of the movement of humpback whales relative to a source

Abstract

When measuring the response of large whales to a noise source, multiple measures of behavior are often used (e.g. horizontal movement, dive profile and surface behavior). Although this helps to determine finescale changes in behavior, using numerous measures means an adjustment of significance level. In addition, many of these behavioral measures do not account for the position of the source vessel relative to the animal or group. This paper develops a new measure, the 'DDsv, which compares the distance of the group to the source vessel had they continued on their original path (expected) to their observed distance to the source vessel. An increase in DDsv implied avoidance. Baseline movements of humpback whales were then compared to a set of controls (where the vessel was moving but the air guns were not operating) and two 'active' treatments: vessels towing a 20 cu in air gun and a 140 cu in array of air guns, air guns firing every 11 sec. This spatially explicit model takes into account the alteration in group horizontal movement relative to the source vessel. It is a measure of displacement behavior that can be applied to other marine mammal behavioral response studies.