All classes of vessels were not implicated equally in the increased level of interactions which occurred in 1978. Cruise ship visitations actually decreased 14 percent in 1978 from the 1977 high, while charter/pleasure craft visitations increased 120 percent between 1976 and 1978. Commercial fishing vessel traffic decreased 30 percent between 1976 and 1978. Charter/pleasure craft were often observed to change direction and travel toward whales for a closer look. Cruise ships and commercial fishing vessels, on the other hand, neither paused for nor actively followed whales. Thus the most likely source for increased interaction would appear to be the increased visitations by charter/pleasure craft in 1978.

This conclusion seems to agree with the perceptions of scientists examining other similar situations. The workshop on problems related to Hawaiian humpback whales, sponsored by the Marine Mammal Commission in 1977, concluded that vessel traffic not oriented toward whales did not ordinarily seem to disturb them. Indeed, it was concluded that whales seem readily to habituate to constant or familiar noises such as those produced by ships of passage. A recent review on the possible effects of noises emanating from offshore oil and gas development concluded that, unlike the abrupt response to sudden disturbances, most whales become habituated to low-level background noises such as would be associated with ship traffic (Geraci, J. R., and D. J. St. Aubin, "Possible Effects of Offshore Oil and Gas Development on Marine Mammals," prepared for the Marine Mammal Commission, August 1979.) Moreover, it was noted that such behavior forms the underlying basis for the success of whale watching cruises. Thus the erratic actions of charter/pleasure craft rather than the more constant action of cruise ships may be the major factor in possible harassment by vessels within Glacier Bay.

Cruise ships also may be implicated as potential sources of disturbance due to the physical setting within Glacier Bay. A direct analogy may be seen in the lagoons of Baja California where gray whales calve. Heavy barge and freighter traffic associated with the salt industry, as well as a dredge operating continuously in the lagoon's mouth, apparently drove gray whales out of Laguna Guerrero Negro between 1957 and 1967. The whales reinvaded in substantial numbers when vessel traffic was eliminated. The continued high use of Laguna Ojo de Liebre by gray whales suggests that the movement of salt barges, beginning there in 1967, may not have been such a nuisance. However, since Laguna Ojo de Liebre is a much larger area than Laguna Guerrero Negro and has a much wider entrance, the whales there may simply have been able to move and coexist next to the barges. Such luxury of space may not be available to the humpback whales of Glacier Bay and, due to geological configurations of its basin, vessel noise may be accentuated there. These factors may account for the unexpected reaction of humpbacks to cruise ships in Glacier Bay.

The apparent departure of humpback whales from Glacier Bay in 1978 and 1979 may also be due in part to a change in the availability of food. Euphausiids have historically been the primary feed within Glacier Bay in July-August, although little research has been done to compare yearly levels of this feed or to determine what level is necessary to support the whales. The only available information derives from vertical plankton tows by the REGINA MARIS in August 1979, which indicated that fewer euphausiids (5 percent) occurred in Glacier Bay as compared to Frederick Sound-Stephens Passage. The humpbacks may have found the Glacier Bay food levels to be too low, particularly in the face of continued high vessel use, and simply departed to search for better concentrations elsewhere.

A similar abandonment of a prime feeding area, the Grand Banks, was observed for the Northwest Atlantic humpback population and was thought to be associated with the overfishing of capelin stocks there. Consequently, the occurrence and distribution of humpback whales may be generally dependent upon the occurrence and availability of its desired prey species.

In a worst case analysis, Glacier Bay is a feeding ground, and its long-term abandonment would not be conducive to the conservation of the humpback whale. Up to 20 or 25 individual whales would relocate to other areas, increasing competition for food there. In such case a greater expenditure of energy might be required to obtain the same quantities of food than would be required in Glacier Bay. An increased energy expenditure would tend to decrease the likelihood of humpbacks successfully increasing their numbers, since growth and the onset of sexual maturity would be delayed.

Conclusions

Our present interpretation of the available data is that uncontrolled increase of vessel traffic, particularly of erratically traveling charter/pleasure craft, probably has altered the behavior of humpback whales in Glacier Bay and thus may be implicated in their departure from the Bay the past two years. Our conclusion, then, is that continued increase in the amount of vessel traffic, particularly charter/pleasure craft, in Glacier Bay is likely to jeopardize the continued existence of the humpback whale population frequenting Southeast Alaska. The alteration in the distribution of the whales in Southeast Alaska can be expected to appreciably reduce the likelihood of the recovery of the North Pacific humpback population, especially when viewed as an incremental aggravation of the problem of humpback/human interaction in general.

Recommendations

Until research reveals the need for more specific action, if any, we offer the following as reasonable and prudent alternatives that the NPS should institute in Glacier Bay to avoid jeopardizing the continued existence of the North Pacific population of humpback whales: