Nice and simple.
But, What if someone catches a skinny disease conger, then someone else lands a nice healthy big Moki which is slightly shorter. Should a moderate length conger really defeat a big Moki?
Maybe have a prize for Longest fish, Most caught and most surprising overall.
The most surprising could be a vote by all that are present. Could get a bit controversial deciding between a 50kg skate and a 600g Gurnard. .