The availability of these and other feeding areas in southeastern Alaska has not been constant over the years. Although Glacier Bay has lately been a prominent feeding area, this was not always so since the area was covered by an ice sheet during the 18th century; at that time the humpback population was presumably at its maximum pre-exploitation level. There is some indication that a seasonal feeding area in Lynn Canal was avoided by humpbacks coincident with the onset of a herring fishery in 1972. With the cessation of that fishery, humpbacks reoccupied the area in 1979. The possibility cannot be discarded that these events are related.
Present Glacier Bay Situation
The NPS records indicate that during 1976 and 1977, 20-24 individual humpback whales moved into Glacier Bay during June and remained there into August. In 1978 this pattern of use changed when most of the animals departed by mid-July. In 1979 this use was modified further with fewer whales entering the Bay and very few of those remaining in the Bay. Observations prior to 1976 are more general in nature, rather than numerical counts of record.
Human use of the Bay is reflected in NPS records, to wit:
| Year | Visitor Days | Large Ships | Private Boats | Fishing Vessels | ||||
| 1965 | 1,800 | |||||||
| 1969 | 16,000 | 115 | ||||||
| 1970 | 30,000 | 165 | ||||||
| 1975 | 72,000 | 113 | 353 | 824 | ||||
| 1976 | 85,000 | 123 | 318 | 656 | ||||
| 1977 | 120,000 | 142 | 534 | 523 | ||||
| 1978 | 109,000 | 123 | 699 | 458 | ||||
Most visitor use is via water access, with cruise ship and recreational craft visitation levels increasing rapidly in recent years.
The recent NPS study indicates that increasing vessel traffic in Glacier Bay may be implicated in the apparent departure of whales from Glacier Bay in 1978 and 1979. Data on the number of observed whale-vessel interactions in Glacier Bay enables calculation of the following "interaction" index (data for 1979 not available):
| Year | Whale-vessel Interactions | Hours Observed | Index (interactions/hour) | |||
| 1976 | 98 | 261.1 | 0.38 | |||
| 1977 | 201 | 407.1 | 0.49 | |||
| 1978 | 268 | 397.5 | 0.67 |
Thus the occurrence of whale-vessel interactions increased 29 percent and 76 percent respectively in 1977 and 1978 over the 1976 base level. Despite mitigative regulations in 1979, observers noted that whale-vessel interactions continued at substantial frequencies.
The NPS data indicate that behavior of the humpback whales in Glacier Bay changed significantly in 1978. Comparison of the frequency distributions of behavioral responses indicates that, whereas distributions were the same in 1976 and 1977, both years were statistically different from 1978. In 1978, more avoidance behavior occurred than in previous years, suggesting that the whales reacted to the increased level of vessel traffic in 1978. However, the causal mechanism for these reactions (whether it be increased noise or visual stimuli) remains unknown.