Annual change of spotted mackerel Scomber australasicus fishing sea-son and fishing grounds in central and southern East China Sea in summer and autumn

Abstract

Annual change of spotted mackerel Scomber australasicus cluster starting time,duration of fishing season,fishing grounds and catch yield were studies and the related impact factors were further explored based on the production data by state-owned large purse-seine in central and southern East China Sea in summer and au-tumn of 2003 2008.The results showed that: the spotted mackerel average starting colony date of fishing season were July 12 in the central and southern East China Sea in summer and autumn.The fishing season usually started in the mid of July and ended by early September,lasting two months,though sometimes it was postponed until late September.The peak of catch mainly occurred in late July and August.Scope of fishing ground varied in the six years with larger fishing grounds in 2005,2006 and 2008,and smaller ones in the remaining three years.Concen-trative degree of central fishing ground was higher in 2003,2004 and 2008.Annual output has great volatility.Catches for the most productive year(2005) was nearly five times that of the least productive year(2007),while the annual difference is more prominent in high-yield fishing areas.The time of spotted mackerel clustering in summer was closely related with the warming speed of water temperature.When temperature increased fast,the fishing season may start earlier.The fishing season duration was in consistent with duration of high temperature.Besides isothermal lines,the central fishing ground was also closely related with the flow direction of Kuroshio Current in East China Sea.The intense volatility of output was not only relevant with its own biomass level,but also with changes in marine environment and fishing factors.