Derived lagrangian statistics on the Vancouver island continental shelf and implications for Salmon migration

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Abstract
Lagrangian trajectories derived from time series data from a small array of current meters are simulated using objective analysis to estimate the velocity field and a fourth‐order Runge‐Kutta scheme to integrate the velocity field to form the particle tracks. This procedure is verified by a direct comparison of actual drifter tracks with simulated tracks; the comparison is excellent. Lagrangian statistics are then computed and used to examine the effects that eddies might have in retaining freely drifting particles. Finally, the implications for the retention of juvenile salmon are discussed. The results suggest that the energy advantage conveyed to juvenile salmon is considerable and significant. Dense aggregations of juvenile Chinook salmon form over certain fishing banks each year off the west coast of Vancouver Island. It is hypothesized that the retention capability of eddies over these banks confers an energy advantage to the juvenile salmon while they wait for the fall transition in the current field and hence a low energy trip on their northward migration.