Flow visualization showing the pathlines of PIV particles seeded in the water as well as the swimming organisms. The depicted particle and animal streaks are the result of overlaying a 30-s sequence of raw PIV images recorded during the middle of a vertical migration. The generated large-scale flow structures next to the downward jet (e.g., blue oval) are significantly larger than the individual organisms. The vignetting of the image is due to the narrow-band laser filter on the camera, which becomes apparent when zoomed out to capture the larger-scale flow structures.