Mate that is an old wives tale and is totally untrue! There is plenty of data out there now thanks to sat tagging and survival rates are very good. A tagged marlin after being tagged generally heads straight for the bottom where it sulks for a few hours but by the end of the day it's up feeding again. This was shown clearly by a skipper on gold coast to be true, he recaptured a marlin he had tagged only 5 hrs earlier! I have never understood where the 10% figure can from but i've heard it from many sorces , interesting though because before sat tagging started they had know idea and no way of telling what the survival rate was after capture! More than likely it was started by people who kept there marlin ( for what ever reason) to justify there decission to do so! But there is no way it was ever based on any real evidence as the data didn't exist!
Ian