Humpback whale sightings were first reported in Glacier Bay in 1899; by the 1930s they were commonly seen in the Bay. Whale numbers typically rise in mid-June, peak in July and August, are somewhat lower in April, May and September and are lowest from October through March. The NPS has monitored and reported on humpback whale population characteristics from June 1 to August 31 each year since 1985 to document the number of individuals identified, residence times, spatial and temporal distribution, calf production, feeding behavior and human/whale interactions including strandings, entanglements in fishing gear and behavioral disturbance. The whale monitoring program also generates whale distribution data used to determine where and when "whale waters" vessel operating restrictions are needed during the summer visitor season. The whale monitoring program covers Glacier Bay and most of Icy Strait, but park waters west of Dundas Bay are not monitored.
Biologists' overall concern is that disturbed whales use energy in reacting to ships, are diverted from previous activity (in Glacier Bay, mainly feeding) and may temporarily move away from preferred habitat or prey patches. It is not known whether whales that tolerate chronic noise exposure undergo stress or are otherwise deleteriously affected. As noted in the NMFS 1993 Biological Opinion, the long term effects of chronic disturbance on the whales' survival and reproduction may never be known. To protect endangered humpback whales from chronic disturbance in Glacier Bay, vessel management regulations are designed to allow NPS the flexibility to incorporate the latest knowledge about underwater noise, whale distribution and behavior into its management actions.