No abstract

Diel vertical migrations are commonly undertaken by juvenile sockeye salmon within pelagic lake nursery environments. Data from hydroacoustic surveys in British Columbia lakes are used to compare predictions from sensory mechanism and selective advantage theories for diel vertical migration with the performance of the animals under field conditions. The observations suggest that light and temperature controlled juvenile sockeye day and night depth positions respectively. A multifactor hypothesis, which interprets the migration as a three-way compromise between foraging, predator avoidance, and the optimization of nocturnal metabolic efficiency, provides the most realistic explanation for the selective advantage of the behavior.

Large numbers of juvenile chinook salmon (Oncorhynchus tshawytscha), chum salmon (O. keta), and pink salmon (O. gorbuscha) were present within tidal channels of a marsh area in the Fraser Estuary between March and June 1978. The tidal channels investigated dewatered at low tide, necessitating daily emigrations by juvenile salmon out of the channels. While pink fry emigrated from tidal channels at the early and middle stages of ebbing tides, most chum and chinook fry emigrated near the later stages of ebbing tides. Mark–recapture studies demonstrated that chinook and chum fry resided temporarily in the marsh prior to migrating into the Pacific Ocean and returned to the same channel on several tidal cycles. Pink fry were abundant in the channels, but appeared to be transient. Chinook and chum showed an increase in average length which was attributable to estuarine growth.Key words: chinook salmon, chum salmon, pink salmon, juvenile residency, marsh tidal channel, Fraser Estuary, estuary growth

Simultaneous comparison of planktivore and crustacean zooplankton distribution patterns in a set of British Columbia lakes suggested coupled diel vertical migration behavior in the two adjacent trophic levels. In lakes where juvenile sockeye salmon performed diel vertical migrations, most zooplankton were non-migratory and concentrated in shallow surface waters over the diel cycle. In contrast, in one lake where pelagic threespine sticklebacks were present, and where juvenile sockeye diel vertical migrations were periodically reversed, most zooplankton undertook diel vertical migrations. The presence of diel vertical migration behavior in zooplankton thus appears to be related to the presence or absence of the behavior in the predominant planktivores.

Dual-beam acoustic surveys of Okanagan Lake suggested active diel vertical migrations of Mysis relicta and kokanee (Oncorhynchus nerka) within the pelagic zone. Mysis relicta were situated between 90–150 m during the day and migrated upwards into the thermocline region of the water column at night. Two groups of kokanee targets were detected. The first undertook a diel vertical migration and coalesced at dusk with a second, shallow-oriented group of targets. Daytime target strength estimates taken while the two groups were vertically segregated in the water column suggested an 8–12 db lower target strength of the deeper group. The results provide acoustic evidence for a smaller body size in the deeper group and the occurrence of an ontogenetic shift in diel migratory behavior of kokanee within Okanagan Lake. Diel comparisons of depth distribution suggested spatial segregation of Mysis and kokanee over much of the diel cycle.