Another explanation for the lack of significant correlation between mesozooplankton biomass and the SOI is related to the choice of the SOI monthly value, (http://www.cpc.ncep.noaa.gov/data/indices/soi) which, in this form, does not take into account the duration of the climatic regime and its consequences on the effect of wind or rainfall anomalies: it is clear that the longer the positive (or negative) SOI, the stronger the effects of La Niña (or El Niño) on western tropical Pacific climate.