POPULATION BIOLOGY OF GNATHOPHAUSIA-LONGISPINA (MYSIDACEA, LOPHOGASTRIDA) FROM A CENTRAL NORTH PACIFIC SEAMOUNT

Large numbers of the lophogastrid mysid Gnathophausia longispina were discovered in 1984 over Southeast Hancock Seamount on the northern Haw aiian Ridge. Additional specimens were collected from the same area du ring subsequent surveys in 1985, 1987, and 1988 to obtain new informat ion on the life history of this species. Estimates of growth suggest t hat G. longispina reaches sexual maturity by its second year. Young ar e brooded by the female for nearly a year and released in late winter- early spring. It is doubtful if G. longispina live longer than 2 yr or produce more than one brood. Most G. longispina are found within 100 m above the seamount summit. The modal progression of size classes ove r time indicates that this species is dependent on local processes rat her than recruitment from other areas to maintain its populations at t he seamount.