Natural changes in the environment and/or in the behavior of whales have occurred concurrently with increased human/vessel activity in Glacier Bay. Such natural changes include spatial and temporal trends or cycles in the physical (temperature, tides, currents, turbidity, etc.), chemical (salinity, dissolved gases, inorganic/organic substances—nutrients, etc.) or biological (primary productivity, zooplankton, nekton, benthic species, predators, etc.) properties or characteristics of the waters within and outside the Bay. Temporal and/or spatial differences in relative abundance of three different prey species within and outside the Bay may have occurred and been responsible, at least in part, for the movement of humpbacks from Glacier Bay. At this time, data are inadequate to relate the movement of humpback whales from Glacier Bay in 1978 and 1979 to physical, chemical, or biological factors. Meeting participants felt that physical and chemical factors were unlikely to have changed sufficiently between 1976 and 1978 to affect humpback whales, while biological factors, perhaps as a result of physio-chemical changes, could have changed sufficiently to have caused or contributed to the movement.
Human activity may have caused changes in the physical, chemical, or biological environment, effecting humpbacks directly or indirectly. Human and vessel activities may have occurred such that the space (vertical and/or horizontal) available to whales for normal activities was less than that necessary (below some threshold level or value). "Too many" vessels may have transited an area and/or approached whales "too closely" for "too long" a period of time, producing visual, acoustic, tactile, chemical, or other as yet unknown stimuli at levels or values (magnitude, intensity, duration, frequency, interval, etc.) greater than the whales would tolerate. The physical-acoustic environment may have changed as a result of sounds produced by vessels. Vessel sounds may be modified, amplified, intensified, etc., as a result of the geological/topographical features of Glacier Bay (and perhaps Lynn Canal as well). Direct interference with the whales' own sounds may have occurred or "environmental" sound levels may have exceeded certain thresholds. Basic data on the acoustic properties and characteristics of Glacier Bay with and in the absence of vessels are lacking.
Changes in water quality may have occurred through pollution. Data are insufficient to document the past or present levels of pollution, but they were thought by meeting participants to be relatively low.
Changes in the biological environment induced by human activity may be contributory to the movement of whales. Movement from Lynn Canal may have resulted from direct competition for the same resource at the same time, by depletion of the resource below levels sufficient to support humpbacks or as a result of noise or the presence of fishing vessels. Fishing activity or overharvesting (depletion of resource) of other species at other trophic levels may indirectly impact humpbacks through the food web/chains. There are insufficient data to prove or disprove such hypotheses at this time.
In summary, a best interpretation of the available data is that uncontrolled increase of vessel traffic, particularly of erratic charter/pleasure craft, may have adversely altered the behavior of humpback whales in Glacier Bay and thus may be implicated in their departure from the Bay the past two years. The causal mechanism of this adverse reaction to increased vessel traffic remains unknown. The effects of increasing vessel traffic apparently are exacerbated by the narrow physical confines of Glacier Bay. This analysis is not clear-cut, however, and may be confounded, at least in 1979, by possible shifts in the occurrence and availability of preferred prey species of humpback whales.
[5] This summary is based on information presented at the meeting and resulting discussions.
ADEQUACY OF EXISTING DATA
In the Background and Possible Cause and Effect sections it was stated that insufficient data exist to indicate cause and effect relationships. Data are not sufficient in many areas, e.g.: