Miniaturization of ovigerous female pink shrimp Pandalus eous off Kanazawa, Ishikawa

Pink shrimp Pandalus eous is an important species and the catch in Ishikawa prefecture (Japan) reaches 700 tons each year. The survey of the young shrimp resources by Ishikawa prefecture fisheries research center revealed that brooding females, includind those caught by commercial Danish seiners, have been miniaturized since 2013, when the year class of 2010, the dominant year class, matured as male. The shrimps of the family Pandalidae are protandrous hermaphrodites and the age of sex transition of some of these shrimps reportedly fluctuates under the influence of sex ratio in the population. The result confirmed that both the miniaturization of the brooding female and the maturation of the male dominant year class occurred simultaneously. Based on the above, we concluded that the brooding female is caused by the lowering of the age of sex transition and spawning in order to increase the female ratio in the population and improve the reproduction efficiency.