1Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, 2Graduate School of Fisheries Sciences, Hokkaido University, Sapporo, Hokkaido 060-0810, 3Aji Marine Station, Seto Inland Sea Regional research Center, Kagawa University, Takamatsu, Kagawa 761-0130 Japan
We conducted 21 replications of sediment trap experiments at a yellowtail Sariola quinqueradiata farm in Uwajima Bay, Shikoku Island, western Japan. Settling fluxes (mass per unit time and unit area) varied from 2.52 to 62.8 g/m2/day and those of the low temperature season (November, December and January) were higher than those of the warm and stratified season (March to August), probably due to vertical mixing in the water column. Yellowtail were provided food as either dry or moist pellets. The settling fluxes where dry pellets were used were lower than those where moist pellets were used. Additionally, the settling flux was determined under an alternative feeding method where fishermen gradually fed yellowtail by hand. Although this technique requires more effort at first, fish neither struggled nor jumped as they acclimated to the feeding regime (non-jump aquaculture method). Our results indicate that organic loading is limited if fish are provided dry pellets under the non-jump aquaculture method.