presentation that each category is discussed sep- 

 arately below. 



Offshore Migrations 



Noctu^-nal fishes. — In many seas, certain reef 

 fishes are known to make extensive feeding mi- 

 grations away from the reef at nightfall; out- 

 standing examples include certain clupeids, po- 

 madasyids, carangids, and other schooling fishes 

 in the Gulf of California (Hobson, 1965, 1968) 

 and tropical Atlantic (Starck and Davis, 1966). 

 These migrations are best known among those 

 nocturnal predators that school on or near the 

 reef during their inactive periods. Although 

 such schooling fishes and their offshore migra- 

 tions during twilight are a major characteristic 

 of some areas, they are not prominent on Kona 

 reefs. This is understandable. The reefs where 

 these schooling fishes and their offshore migra- 

 tions are so pronounced in the Gulf of California 

 and in the tropical Atlantic are surrounded by 

 extensive open sand flats or grass beds. These 

 vast stretches are nocturnal feeding grounds of 

 the fishes that migrate away from the reefs. 

 The importance of proximate feeding grounds 

 of this sort to such fishes is well known (Longley 

 and Hildebrand, 1941; Randall, 1963; Hobson, 

 1968) . Similar feeding grounds do not surround 

 Kona reefs, which are instead bordered by a 

 precipitious drop into deep water. Not surpris- 

 ingly, the relatively few species that migrate off- 

 shore at nightfall from Kona reefs, including 

 Priacanthus cruentatus and Myripristis spp., 

 seek open-water prey. Furthermore, whereas 

 fishes migrating over the extensive sand flats and 

 grass beds adjacent to reefs elsewhere often 

 travel considerable distances (Starck and Davis, 

 1966; Hobson, 1968) , comparable data are not 

 available for Priacanthus and Myripristis. It 

 is possible that these fishes do not go much be- 

 yond the outer edge of the reef, an area known 

 to be a rich feeding ground for diurnal plankton- 

 feeding fishes (see below). 



Diurnal fishes. — Offshore feeding migrations 

 comparable to those made by nocturnal fishes 

 have not been reported for diurnal fishes. In 

 the Gulf of California, the exodus of fishes away 



FISHERY BULLETIN: VOL. 70, NO. 3 



from the reef during twilight, transforming the 

 stretches of open sand offshore into centers of 

 activity, is strictly a nocturnal phenomenon; 

 there is no diurnal equivalent, as these open ex- 

 panses are comparatively without active fishes 

 in daylight (Hobson, 1968). 



In Kona, several diurnal fishes, including some 

 individuals of the surgeonfish Naso hexacanthus 

 and the damselfish Chromis verater, migrate to 

 the offshore edge of the reef during morning 

 twilight. They swim to where the seaward reef- 

 face drops abruptly to great depths and here 

 become part of a large assemblage of plankton- 

 feeding fishes. Apparently plankton is excep- 

 tionally rich in this area. The migrations seem 

 to terminate here, but the larger Naso hexacan- 

 thus, and perhaps other species, periodically 

 range farther offshore during the day. During 

 evening twilight many individuals of these spe- 

 cies return inshore to the shallower parts of the 

 reef, a pattern obscured by the many other in- 

 dividuals of these species that shelter themselves 

 on the offshore parts of the reef, below their mid- 

 water feeding grounds. It may be that there is 

 not enough suitable cover here to accommodate 

 all of the many fishes that concentrate to feed 

 in this location. This would account for the fact 

 that while some shelter themselves here, others 

 migrate from other areas. 



Intrareef Migrations 



Conspicuous elements of the transition period 

 are the long drawn-out processions that migrate 

 from one point on the reef to another, following 

 the same routes day after day. Although the re- 

 distribution pattern achieved by these move- 

 ments remains undefined, the phenomenon seems 

 limited to herbivorous fishes, especially the small 

 to medium-sized acanthurids and scarids, and to 

 some plankton feeders. Herbivorous reef fishes 

 are widely reported to be strictly diurnal (Hob- 

 son, 1965, 1968; Starck and Davis, 1966). The 

 migratory patterns shown by these fishes are ob- 

 scured by the many other individuals of the mi- 

 grating species that do not join these move- 

 ments. 



Some herbivorous species, for example certain 

 parrotfishes (see Bardach, 1958), range far 



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