Feeding rhythm and vertical migration of the euphausiid Euphausia pacifica in coastal waters of north-eastern Japan during fall

We investigated the feeding rhythm and diel vertical migration of Euphausia pacifica in coastal waters of north-eastern Japan in September 2000. The euphausiids arrived at the surface early in the night and sank just after satiation. Gut pigment contents and stomach fullness were higher in the food-rich surface layer at night than in the food-poor deep layer during the day. Feeding activity of E. pacifica during daytime was low even if food organisms were abundant in the ambient water in the top 50 m. Therefore, the feeding rhythm of E. pacifica is explained by decreased feeding activity during the day rather than by reduced food availability.