STRUCTURE AND ORGANIZATION OF LOCAL MIGRATIONS IN BROWN SURGEONFISH (ACANTHURUS-NIGROFUSCUS)

In the northern Red Sea (Gulf of Aqaba, Israel), brown surgeonfish (Ac anthuridae: Acanthurus nigrofuscus) migrate, in small groups, up to 1. 5 km each day from nocturnal shelters to feeding sites in the morning, and from feeding sites back to shelters in the late afternoon. During the summer spawning season, groups of these fish undertake an additio nal migration of up to 1 km to and from sites of mass-spawning aggrega tions. The total number of fish migrating to the Laromme feeding site was relatively stable ((X) over bar = 1018) throughout the study perio d (1988-1990). By contrast, the number of fish arriving at the Lightho use spawning site fluctuated drastically (similar to 50 - > 2000), wit h the largest number of fish recorded around the new moon and the lowe st within 1-2 days of a full moon. Durations of the migrations to and from the feeding site were similar, as were the numbers of groups arri ving and departing the feeding site. In contrast, the duration of migr ation and number of groups were much greater during arrivals at the sp awning site than during departure, due to an explosive emigration from the sire following mass spawning. Arrival and departure routes differ ed at both feeding and spawning sites, demonstrating that simple route -reversal is nor practiced by these fish. Exchanges of position by lea ding and following fish in groups were rare, suggesting that leadershi p may play important roles in determining specific routes. Surgeonfish returning from spawning in early evening ceased migrating at a specif ic time, rather than a specific place, and completed their homeward-bo und migrations the next morning.