Stocking effectiveness of Japanese Spanish mackerel Scomberomorus niphonius in the eastern Seto Inland Sea

Abstract

In order to estimate the stocking effectiveness of Spanish mackerel Scomberomorus niphonius 36-40 mm (40 mm group) and 93-150 mm (100 mm group) in total length were marked on the otolith with alizarin complexone and stocked in the eastern part of the Seto Inland Sea in 2002 and 2003. Through a survey at the major landing markets in the area, the contribution rates of stocked fish to the total landings for 0 and 1 year-old fish were estimated to range from 4-42% and the total amount of landings from stocked fish ranged from 8.3 to 21.6 tons. Stock enhancement of Spanish mackerel was shown to substantially contribute to the fisheries production of this species. Recapture rates until 1 year-old fish were estimated at 0.89-15.75% and the economic efficiency ranged from 0.14 to 1.60, showing that stocking the 100 mm group in 2003 was profitable even for 1 year-old fish.