Archipelago-wide episodic recruitment of the file fish Pervagor spilosoma in the Hawaiian Islands as revealed in long-term records
The endemic filefish, Pervagor spilosoma, has long been known to recruit infrequently but in large numbers to shallow water habitats in Hawaii. When it does recruit, as it did in 1944, 1975 and 1982–1987, it becomes the most abundant or one of the most abundant species on Hawaiian reefs. At these times of high abundance, juvenile individuals also become abundant in the off-shore pelagic environment and in deeper benthic habitats. The results of two previously published studies and this one show that the last heavy recruitment occurred throughout the Hawaiian Island chain in the period from 1982–1988. The earliest strong recruitment in this interval occurred on the leeward, or northwest Hawaiian Islands in 1982, then on Oahu in 1983, then on the island of Hawaii, at the southeast end of the island chain in 1985. At the Kaneohe Bay, Oahu, sampling site, strong recruitment occurred in 1983–1987. Fish that had recruited in the summer of a year survived less than a year at these shallow (<15 m) sites or moved off the reefs. No other fish species among the 30 species censused in a 20 year period at Kaneohe Bay has shown the extremes of abundance displayed by this species, nor did any other species recruit so strongly in the 1983–1987 period. The latter event suggests that the pattern of recruitment in this species was not solely due to a particular pattern of ocean circulation, because if that were the case, other species would also show strong recruitment. The rarity of large recruitment events in this species, the high density of the recruits, the length of individuals at recruitment, the observation by others of juveniles and possibly young adults in the water column, and the sequential nature of the recruitment down the length of the island chain may in part be the result of metamorphosis in the pelagic environment and a pelagic juvenile stage in this species.