Recent publications have shown that river runoff and wind mixing are two major environ¬mental factors affecting productivity of fish populations in subtropical and tropical areas, as op¬posed to water temperature in colder waters. In the present paper, we compare the variability of seawater temperature, river runoff and wind mixing in three different seas: a subtropical sea (the Mediterranean) and two cold seas (the North Sea and the Baltic). Temperature variability de¬creased from colder to warmer areas. The highest temporal variability in the river runoff corre¬sponded to rivers flowing into the Mediterranean, and the lowest corresponded to rivers flowing into the North Sea and the Baltic Sea. The variability in the wind mixing index (cube of the wind speed) depended on the area under consideration, and attained maximum values in the Cap Bear station (northwestern Mediterranean). The effect of these regional variability differences in environmental factors on fisheries production is briefly discussed.Investigaciones recientes demuestran que las descargas fluviales y los vientos son factores ambientales cla¬ve para la productividad de las poblaciones explotadas en zonas subtropicales y tropicales, mientras que en mares frios la temperatura del agua constituye el factor ambiental m^6^s importante para la productividad pes¬quera. Este estudio compara las diferencias geogrάficas en la variabilidad temporal de tres factores fisicos (tem¬peratura del agua,, aportes fluviales y velocidad del viento) en un mar subtropical (Meditermneo) y dos ma¬res frios (Mar del Norte y Baltico). La variabilidad temporal de la temperatura del agua es mayor en los dos mares frios que en el subtropical. Asi mismo, los rios que desembocan en el Mediterrάneo presentan mayor va-