Daily migrations of a coral reef fish in the Red Sea (Gulf of Aqaba, Israel): Initiation and orientation

Brown surgeonfish (Acanthurus nigrofuscus) in the Red Sea near Eilat, Israel, undergo daily migrations of up to 1.5 km to feeding sites throughout the year and to spawning sites during June through August. We investigated, by observation and experimentation, the cues that initiate migrations to spawning and feeding sites. We also examined the possible roles that odors, the sun, electromagnetic detection, and landmarks have in determining the routes fish take to the various sites. Initiation of spawning migrations to one spawning site was correlated to the time of sunrise, sunset, and tidal cycle. Fish feeding north of this same site initiated their migrations simultaneously, whereas those feeding south of the site initiated migrations in order of their distance from the site, from distal to proximal, so as to arrive on the spawning grounds more or less simultaneously. This latter observation, and the fact that group size increased as fish move closer to the spawning site in the south but not the north, indicated that social interactions may also play an important role in initiating migrations in some local groups. We were unable to identify factors that influenced initiation to a second spawning site. Migrations to feeding sites appeared to be initiated by sunrise and sunset. Routes to feeding or spawning sites were not determined by odor, sun compass, or electromagnetic detection. Fish key on specific landmarks during migration, but their reliance on particular landmarks can be reduced if the landmarks were moved more than 6 m from their original location. Although surgeonfish usually followed a sequence of landmarks to particular sites, their ability to navigate to feeding or spawning sites after key landmarks were manipulated suggests that there were redundancies in the cues used.