Zooplankton resources and humpback whale (Megaptera novaeangliae) feeding ecology in South-East Alaska

Recent population changes on the SE-Alaska humpback whale (Megaptera novaeangliae) feeding ground may be explained as being primarily due to large-scale oceanographic variations that locally affect plankton productivity. It is suggested that the 1978 whale decline in Glacier Bay was due to localized nutrient limitation caused by climate (El Nino)-induced changes in this fjord's circulatory pattern. An assessment of zooplanktonic prey in Frederick Sound in summer 1983 was integrated into a long-term monitoring project of the area, and showed generally similar conditions as the previous season. A slight increase in the krill proportion of plankton swarms, small changes in krill species composition, and the occurrence of a Southern-origin copepod species were the notable exceptions. A comparison between zooplanktonic feeding and non-feeding targets suggested euphausiid biomass (mainly Thysanoessa raschii) to be the most likely stimulus for whale feeding activity. Examination of humpback whale fecal material proved a valuable method to identify dietary components. The local developmental pattern of T. raschii was investigated with regard to its noted importance in humpback whale diet. Dominant life history stages found in 1983 indicated sub-optimal environmental conditions, possibly related to increased coastal warming. Three sub-cohorts were identified in the spring spawning cohort, and developmental timing appeared to be correlated with the whales' migratory pattern.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat