So, this round some of the mermaids are living, some are dead. Wei Wuxian would only really get remit over the dead ones. And not all of them.

All that said, I can give you a few. Call it 10 for two hours?

Given you're dealing with a heavy-duty number of mermaids ready to swarm, I'd say your idea to have them going ahead and spooking the incoming boats is probably more cost-effective. If you pit them against their sisters, they'll probably get killed quicker.

You can keep replenishing them up to 10 if they die off during the two-hour interval? But I would say no more than 20 dead mermaids used for this endeavour.