Date of Award
Fall 2024
Project Type
Thesis
Program or Major
Biological Sciences
Degree Name
Master of Science
First Advisor
Michelle EH Fournet
Second Advisor
Easton R White
Third Advisor
Russell G Congalton
Abstract
Vessel disturbance impedes the resilience and recovery of humpback whale (Megaptera novaeangliae) populations. Many management strategies in Southeast Alaska aim to protect whales and their habitat. However, it is difficult to measure the effectiveness of management strategies without understanding the state of an ecosystem with minimal vessel traffic. The thesis examines two situations with reduced vessel activity to understand humpback whale behavioral and acoustic ecology. We first use the Beardslee Island Complex and adjacent waters in Glacier Bay National Park and Preserve (Glacier Bay), an area with minimal vessel traffic, to understand habitat use by foraging and traveling whales. Using data from theodolite surveys, we conducted a kernel density estimation to identify areas associated with each behavior state. We then analyzed environmental characteristics associated with each habitat using generalized linear mixed models (GLMMs). With minimal vessel disturbance, we found whales minimize energy expenditure by foraging along islands in shallow water and minimizing travel distance in a high-current channel. Quantifying how whale space use varies with behavior state can inform mitigation measures on other foraging grounds, particularly those with high levels of vessel traffic. For the second part of the thesis, we focused on a period with reduced tour vessel traffic, the Anthropause, to compare the soundscape (all sound in an ecosystem) of two humpback whale foraging areas with contrasting vessel management strategies: Glacier Bay (stringent vessel management) and North Pass in Juneau (standard vessel management). Passive acoustic data were recorded at each site during the summers of 2020-2022 (Anthropause Year, Transitionary Year, and Rebound Year). We calculated broadband (dBRMS 50Hz-12kHz re 1 μPa) and power spectral density (PSD; dB50Hz- 12kHz re 1 μPa2 Hz-1) sound levels for each year and site. We then manually annotated the acoustic presence of whales and vessels. Changes in the soundscape were driven by changes in vessel traffic. Even in the absence of cruise ships, smaller vessels still substantially impacted sound levels and humpback whale detectability. Ambient sound levels increased in both sites following the Anthropause, but Juneau was louder than Glacier Bay across all years. We also found that whales vocalizations were less likely to be detected when vessel noise was present in all deployments. Overall, we detected more whale vocalizations in Glacier Bay than in Juneau. Management strategies in Glacier Bay (i.e., daily vessel quotas, dynamic and static slow zones, etc.) mitigated the impact of vessels on the soundscape substantially better than Juneau. To reduce the acoustic disturbance of vessels, managers outside of Glacier Bay could evaluate how to implement some of these mitigation measures. The findings presented in the thesis can be used to inform potential management practices in the entirety of Southeast Alaska and have broad implications for other humpback whale feeding grounds.
Recommended Citation
Smith, Melanie Anabel, "Understanding Ecological Baselines to Inform Humpback Whale (Megaptera novaeangliae) Management Strategies in Southeast Alaska" (2024). Master's Theses and Capstones. 1900.
https://scholars.unh.edu/thesis/1900