Effects of lunar phase and habitat depth on vertical migrationpatterns of the sergestid shrimp Acetes intermedius

ABSTRACT:   The effects of lunar phase and habitat depth on the verticalmigration patterns of the sergestid shrimp Acetes intermedius wereexamined based on seven field observations in coastal waters offsouth-western Taiwan. The results indicate that the pattern of nocturnalvertical movement of A. intermedius depends on the lunarphase. The shrimp evaded moonlight during the ascending period andthen the moon was used as a trigger for resuming an ascent towardsthe sea surface or descending towards the 10 m water layer.During the descending period, A. intermedius moved rapidlyto the bottom or to a middle water depth at 50–80 mbefore sunrise. However, A. intermedius in waters of deepKaoping Canyon can also perform a slow descending migration thatcoincides with photosynthetically active radiation of 4 µmol/sper m². Because the density of A. intermedius onthe surface layer is affected by moonlight, the lunar phase is oneof the factors affecting the catch rate of large-skimming nets duringthe night in waters off south-western Taiwan.