All I know is that it means you lost a fish. People have been saying that forever on the party boats in So-Cal.

We used to call people sabanero when they missed a fish too. That one came from a guy we knew in high school who had a huge mullet. We figured he was growing his hair out to sell it so we called him sabanero de pelo, or just sabanero for short. Try it out on your friends when they miss a fish some time. Just yell sabanero! Utter confusion.

You may also be interested in the fishing slang guide:
http://www.calfishing.com/barni/fishing_slang.html