South Korean fishing boats in the Yellow Sea
April 3, YEONPYEONG Island, South Korea — South Korean fishing boats sail toward a blue crab fishing ground in the Yellow Sea on April 3 amid heightened tensions over North Korea’s planned rocket launch. (Yonhap)

Notice the ROK Navy ship in the background.  These fishermen work along the Northern Limit Line (NLL), across which is the north Koreans.  Blue Crab is expensive, and battles in 1999 and 2002 prove that both sides are willig to die to enforce their maritime claims.