Humpback whale habitat use patterns and interactions with vessels at Point Adolphus, Southeastern Alaska

Abstract

Humpback whales at Point Adolphus, in southeastern Alaska, are faced with the challenge of maximizing their energy gain from feeding and minimizing energy losses that can occur due to disturbance by vessel traffic. Point Adolphus is unique because of abundant prey resources that attract high concentrations of humpback whales during the summer and high levels of vessel activity. Using scan sampling and focal behavior observation sessions data were collected from an elevated shore station on the northern coast of Chichagof Island in 2001. Humpback whale numbers peaked during early ebb tide. Whales were distributed west during ebbing tides and east during flooding tides. During flood tides, humpback whales exhibited non-directional movement. Differences in humpback whale numbers, distribution and movement patterns in relation to tide appeared related to small-scale fronts and headland wake effects associated with Point Adolphus. Overall, humpback whale swimming speeds were faster when the number of vessels present was greater and distance to the nearest vessel was smaller. However, responses of individual whales differed. Humpback whales at Point Adolphus appear to have developed strategies to exploit predictable times to feed which are tidally-induced and practice short-term avoidance strategies that may reduce the effects of vessel traffic.