Stock separation study using otolith Sr/Ca ratio on ayu Plecoglossus altivelis captured from the Ioki River and the Monobe River

Abstract

A stock separation study on ayu Plecoglossus altivelis captured from the Ioki and the Monobe rivers was conducted using the otolith Sr/Ca concentration ratio method. Discrimination among amphidromus, hatchery-cultured and landlocked populations was possible by comparing with chart patterns during early life stage, because the rearing salinity of hatchery-cultured fish is intermediate between those of amphidromus and landlocked populations. When stock separation was carried out by both otolith Sr/Ca ratio and mark-releasing with 85 individuals, disagreement between them occurred for only 9 individuals. It is indicated that stock separation by the method of otolith Sr/Ca ratio is as effective as the conventional mark-releasing method.