PERSISTENCE OF EGG POCKET ARCHITECTURE IN REDDS OF CHUM SALMON, ONCORHYNCHUS-KETA

Analysis of frozen cores of gravel surrounding the egg pockets of chum salmon, Oncorhynchus kern, collected in the fall revealed that spawni ng activity by females purged about 75%, of the fine sediments from th e stream bed. The egg pocket was one of four distinct vertical strata detected in the cores. There was an undisturbed layer below the egg po cket, and separate bridge and cover strata above the egg pocket, all d efined by different particle size distributions. However, by spring mo st of the egg pockets had been infiltrated with fine sediment and the particle size distribution approached background levels. The most like ly physical factors responsible for these results were: (1) intrusion of fine sediments through the cleaned surface gravel, (2) lateral subs urface migration of fine sediment into interstitial voids, (3) scour o f the surface gravel and subsequent deposition of a sand rich bedload: and (4) superimposed spawning activity of other fish, causing disturb ance of the cleaned surface gravel and exposing the egg pocket to intr usion of fine particles. We conclude that, while female salmon substan tially affect the physical environment of their embryos, subsequent se diment transport processes and fine bedload flux tend to return this e nvironment to pre-spawning conditions.