Structure and Organization of Local Migrations in Brown Surgeonfish ( Acanthurus nigrofuscus)

In the northern Red Sea (Gulf of Aqaba, Israel), brown surgeonfish (Acanthuridae: 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 additional migration of up to 1 km to and from sites of mass‐spawning aggregations. The total number of fish migrating to the Laromme feeding site was relatively stable (X̄ = 1018) throughout the study period (1988–1990). By contrast, the number of fish arriving at the Lighthouse spawning site fluctuated drastically (˜50‐ > 2000), with the largest number of fish recorded around the new moon and the lowest 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 arriving and departing the feeding site. In contrast, the duration of migration and number of groups were much greater during arrivals at the spawning site than during departure, due to an explosive emigration from the site following mass spawning. Arrival and departure routes differed at both feeding and spawning sites, demonstrating that simple route‐reversal is not practiced by these fish. Exchanges of position by leading and following fish in groups were rare, suggesting that leadership may play important roles in determining specific routes. Surgeonfish returning from spawning in early evening ceased migrating at a specific time, rather than a specific place, and completed their homeward‐bound migrations the next morning.