Swimming depth of migrating silver eels Anguilla japonica released at seamounts of the West Mariana Ridge, their estimated spawning sites

Five hormone-treated female Japanese silver eels Anguilla japonica were tag ged with ultrasonic transmitters and released by submersible in the West pa cific at seamounts of the West Mariana Ridge, their supposed spawning groun ds. Four eels were tracked for 60 to 423 min in the vicinity of the seamoun ts. They did not settle at the seamounts but swam at a mean speed of 0.37 m s(-1) into open water above deep ground. Their mean swimming depth ranged from 81 to 172 m. Experiments suggest that pre-matured A. japonica migrate to their spawning grounds in temperate warm water and at shallow depths.