The catch of ribbonfish Trichiurus lepturus in the coastal waters of south-western Taiwan has significantly declined in recent years. To examine the effects of exploitation on the feeding habits of ribbonfish, 1570 specimens were collected on a monthly basis during March 2002-March 2003 from the landings by trawlers operating in the coastal waters of south-western Taiwan. The size of the ribbonfish ranged from 83-298 mm preanal length (PL), with a peak at 201-250 mm PL. Although they fed on shrimps and squid, fishes including Benthosema pterotum, Bregmaceros lanceolatus and Encrasicholina heteroloba were their main food items. In particular, B. pterotum was the most important food all year except during summer. No evidence of cannibalism was found in this study. No differences between day and night were found in the feeding activity of T. lepturus. However, B. pterotum and Acetes intermedius were the most important prey in the daytime, whereas B. lanceolatus, B. pterotum and E. heteroloba were at night. Feeding activity and the number of food items increased with increasing size of ribbonfish. Their feeding intensity in February to June, the main spawning season, was significantly greater than in other months. Changes in the food and feeding habits of this species before and after the recent period of heavy exploitation are discussed in detail in this study.

SUMMARY: Spatio‐temporal variation of the sergestid shrimp Acetes intermedius in the coastal waters of southwestern Taiwan was investigated based on 1546 samples collected by 13 commercial fishing vessels from July to October 1996. Adult sergestid shrimp started a down‐estuary migration with the increased river discharge associated with heavy summer rainfall. Fishing season for this species was to commence after that. In July, the shrimp stock was found on the shallow continental shelf off Tungkang and Fangshan. They mainly aggregated in Kaoping Canyon off Tungkang during August and September occurring at very high densities. In October, the shrimp returned to the coastal waters off Tungkang and Fangshan at lower densities. The heavy rainfall is a factor that triggers the shrimps to make a down‐estuary migration that could reduce competition for food between adults and their offspring during the period of high river discharge. When the northeast monsoon prevailed, the sergestid shrimp moved back to the estuaries and the fishing season was terminated.

Kawakawa Euthynnus affinis is the most abundant species among the small tuna in the coastal waters of Taiwan. The migration pattern of kawakawa to Taiwan was determined in the present study based on the species' feeding habits and reproductive biology and on temporal variation of catch for kawakawa and its prey fishes. Schools of this species successively migrate to Taiwan from September to May, and then move away in June. They travel to the waters off Taiwan with the warm Kuroshio current, migrate toward coastal waters for feeding and move away for spawning. It is suggested in the present study that the kawakawa spawning ground is in the waters of the northern Philippines. The migration of kawakawa exhibits size-segregating behavior. Schools of immature young fish first arrive in the coastal waters around Taiwan, followed by the adults.

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.

The stomach contents and feeding habits of the Taiwan mauxia shrimp Acetes intermedius were examined based on 420 specimens collected in the costal waters of south-western Taiwan. Two 24-h periodic samplings of specimens were completed to describe the diel feeding periodicity of this species. Phytoplankton was the main food for the Taiwan mauxia shrimp, and the dinoflagellates was the most important food. They also fed on zooplankton and amorphous materials. Their diet changed with the seasons. The feeding activity of this species mainly occurred at night. The results obtained in this study supported the hypothesis that A. intermedius performs a nocturnal vertical migration to avoid predators and to allow for safe feeding.