The Hawaiian filefish, Pervagor spilosoma, is normally a rare fish on the reefs, but several times each decade it reproduces en masse and juveniles become one of the most abundant species around.
New research from John Stimson, of the University of Hawaii's Department of Zoology has looked at the long-term abundance of the fish on Hawaiian reefs in an effort to explain why it breeds episodically.
Stimson's paper, which has just been published in the journal Environmental Biology of Fishes, explains that P. spilosoma breeds infrequently in the shallow waters off Hawaii, but when it does, the numbers of offspring can be so large that the species becomes the most common one on the reefs.
Previous records have shown that the filefish bred massively in 1944, 1975 and between 1982 and 1987. At these times, the fish was so abundant that it was found in the off-shore pelagic environment and in deeper benthic habitats, as well as on the shallow coral reefs.
No other species has been found to become so abundant on Hawaii's reefs at specific times, and the times at which the fish bred, didn't see other species spawning en masse at the same time.
When the fish last spawned en masse, between 1982 and 1988, scientists found that the earliest fish to breed were those on the northwest Hawaiian islands. Later on, in 1983, the P. spilosoma on the island of Hawaii started to breed, with those further away on the southeast end of the Hawaiian island chain finally spawning in 1985.
Stimson says that the strong episodic recruitment (or mass production of offspring) seen in spilosoma can't be explained by ocean currents, since strong recruitment hasn't been recorded in other species at the same time.
Instead, Stimson believes that other factors could be responsible for this unusual reproductive event.
Says Stimson: "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.
For more details see the paper: Stimson, J. (2005) - Archipelago-wide episodic recruitment of the file fish Pervagor spilosoma in the Hawaiian Islands as revealed in long-term records. Environmental Biology of Fishes, 72 (1): 19-31, January 2005.