Simulation of juvenile sockeye salmon (Oncorhynchus nerka) migrations in the Strait of Georgia, British Columbia

Abstract

Previous research has documented two main migratory routes of juvenile sockeye salmon (Oncorhynchus nerka) through the Strait of Georgia, British Columbia, Canada, and large interannual variability in marine survival rates of the Chilko Lake stock. Simulation models were used to explore the influence of surface currents on the migratory route of juvenile sockeye salmon (smolts) through the Strait of Georgia. We used a model of downstream migration to generate daily numbers of Chilko Lake sockeye salmon smolts entering the Strait of Georgia, based on daily counts of smolts leaving the rearing lake. A numerical hydrodynamic model (driven by surface wind, tide, and Fraser River discharge) hindcasted surface currents in the Strait of Georgia on a 2 km × 2 km grid. A smolt migration model simulated fish moving through the Strait with different compass‐oriented migratory behaviours (i.e. swimming speed and directional orientation) within the time‐varying surface advection field. Results showed that surface currents within the Strait of Georgia can affect the migratory route of sockeye salmon smolts in spite of their large size (8 cm). Wind is the forcing mechanism primarily responsible for determining which migratory route would be used. Under prevailing wind conditions (i.e. toward the north‐west), most sockeye salmon smolts would use the eastern migratory route; however, relatively brief south‐eastward wind events (lasting about 2 days) would force most smolts into the western migratory route. Given the heterogeneity of food for salmon within the Strait, we hypothesize that wind‐driven variability in the annual proportion of smolts that use the western and eastern migratory routes in the Strait of Georgia affects early marine survival rates of Fraser River sockeye salmon.

Fraser river sockeye salmon marine survival decline and harmful blooms of Heterosigma akashiwo

“…mainland coast with no stock-specific route preference (Groot and Cooke, 1987;Groot et al, 1989;Welch et al, 2009). Simulation models indicated that surface currents within the Strait affect the seaward migratory route of Fraser River sockeye smolts (Peterman et al, 1994). Prevailing northwest wind conditions in spring and early summer would force smolts along the eastern shore of the Strait.…”

An evaluation of the potential influence of SST and currents on the oceanic migration of juvenile and immature chum salmon (Oncorhynchus keta) by a simulation model

“…These results suggest that in winter, the effect of wind on the migration pattern of the Asian and East Kamchatkan chum salmon is greater than that on the North American chum salmon. Peterman et al. (1994) also suggested that the most important physical factor that influences the migratory route of juvenile sockeye salmon is the direction and strength of the surface winds during their early marine life stage.…”

“…Modeling studies have been shown to be an appropriate method to investigate the influences of several factors upon salmon migration. Peterman et al. (1994) showed the influence of surface currents on the migratory routes of juvenile sockeye salmon ( O. nerka ) using a model that was coupled with a two‐layer hydrodynamic model.…”

Effects of tidal currents on Pacific salmon migration: results from a fine-resolution coastal model

“…Spatially explicit individualbased models (where spatial locations are included) have been used in fisheries oceanography to investigate the fate of eggs and larvae (e.g., Bartsch et al 1989;Davidson and deYoung 1995;Hermann et al 1996;Hinckley et al 1996) and in fish migration studies (e.g., Fiksen et al 1995). This methodology has been applied to study sockeye salmon both in the ocean (e.g., Dat et al 1995) and in estuaries (e.g., Peterman et al 1994). The method used for these spatially explicit models was to combine a hydrodynamic model (yielding current fields) with a model of larval or fish behaviour (tracking particles and adding behaviours).…”