El Niño related to changes in sardine spawning

[Toni Cruzado]

The Pacific sardine, an important species for commercial fishing, spawns off the coast of California. The area and quality of its spawning habitat have been observed to vary from year to year, sometimes changing with El Niño– Southern Oscillation conditions, but smaller- scale mechanisms also play a role. To sort out the physical forcing mechanisms affecting sardine spawning, Song et al. used data assimilation, combining observational data on sea surface height, sea surface temperature, and salinity data with a physical ocean model. They then looked at how the physical mechanics could explain observed interannual variations in sardine spawning range and egg density.

The researchers found that increased wind- driven offshore transport during the April 2002 and 2007 La Niña conditions led to extension of the sardine spawning habitat farther offshore. In contrast, in April 2003, under El Niño conditions, spawning habitat was smaller but of higher quality, leading to a higher density of eggs and greater survival of larvae. Although there are still unknown factors that control sardine egg distribution, the work advances understanding of interannual variability in sardine spawning. (Journal of Geophysical Research- Oceans, doi:10.1029/ 2011JC007302, 2012) —EB

(From Eos, Vol. 93, No. 17, 24 April 2012)