Recherches sur la situation trophique d'un groupe d'organismes pélagiques (euphausiacea). II. Comportements nutritionnels

Analysis of the fluctuations of the repletion index of stomachs over a 24 h period allowed us to establish the main features of the feeding behaviour for the most abundant species of euphausiids inhabiting the equatorial and south tropical Pacific Ocean. Although feeding activity never stops completely, its intensity shows usually a rhythm, revealed by a sinusoid-type curve of the repletion index. This rhythm, in most cases, is not synchronous with the day-night alternation; for several species, an increase of the feeding activity is evident as early as 14.00 hrs, i.e., long before the nocturnal ascent of animals toward the surface, when they are still concentrated in the 300 to 600 m water layer. By integrating the data for 9 species, it is shown that the search for food is, as a whole, most active by night (20.00 to 6.00 hrs) in the subsurface layers, but is also quite intense between 14.00 and 20.00 hrs in intermediate and deep layers (300 to 600 m).