Board Thread:Game Updates/@comment-1820055-20150930021406/@comment-26850872-20151009150935

http://akankore.doorblog.jp/archives/45654471.html

Apparently there's also another quest that if you manage to catch up to 30 sauries, you'll get a "Big Catch Flag" (大漁旗) and the Type 4 Passive Sonar.