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| In the migrating case, upwelling advects surface waters offshore, but the individuals spend a part of the day in deeper waters which are advecting onshore. The initial seeding of the population was of small, relatively non-migratory individuals. As they grow, they develop increased ability to migrate vertically. Individuals initially seeded into deep waters with little food eventually starve and are removed from the model. Some individuals grow slowly, develop limited swimming ability and seek a mid-depth (balancing their prefered nighttime and daytime depths). Most reproduction of migrating individuals occurs nearshore where food concentrations (upper panel) are greatest. The ability of the progeny to remain nearshore depends on the dynamic balance between growth rate and offshore advection rate. If they grow fast, they start to migrate to deeper waters during the day, and this improves their chances of remaining nearshore. Note the near absence of individuals offshore. Shift-Click (Netscape Users) here to retrieve an flc animation of daily snapshots of the model output. |