Schools of Pacific sardines spawn in the cool waters off the California coast. Previous studies suggest that the fish would thrive in large-scale eddies that are common in the California current system, but the effects of eddies and streamers on sardine survival remain unclear. Do sardines survive there because eddies contain suitable habitat or because an inherent property of eddies confers some kind of advantage—and does this advantage translate into healthy adult populations?
Nieto et al. now demonstrate that eddies and streamers simply entrain coastal waters that form ideal sardine habitat, carrying the developing larvae offshore. To determine this, the researchers combined ship-based observations of sardine eggs with satellite measurements of sea surface temperatures, chlorophyll concentrations, and ocean circulation. They also used a statistical model to evaluate the importance of different environmental factors.
The researchers expected that expanded spawning habitat would benefit sardine populations, especially because the small fish can theoretically survive in the open ocean. However, their results showed just the opposite. When the scientists compared the offshore extent of spawning habitat to an index of sardine recruitment success, they found that larval sardines fared worse the farther from shore they were transported.
The researchers hypothesized that this may occur because it becomes increasingly difficult for young sardines to migrate back to coastal waters. Their results refocused the view that eddies are beneficial to survival to a new perspective that eddies and streamers are a sink for sardine offspring where offshore transport leads to poor survival. (Journal of Geophysical Research: Oceans, doi:10.1002/2014JC010251, 2014)
—Julia Rosen, Freelance Writer
Citation: Rosen, J. (2015), Survival of young sardines flushed out to open ocean, Eos, 96, doi:10.1029/2015EO025295. Published on 4 March 2015.