Whats needed are huge robotic winged beach marshals carrying state of the art salt water fish tanks and weigh scales. They could patrol the beach by flying up and down hunting out fish for weighing as they are being landed. They could catch and return as well as communicate weights and sizes to a central computer that runs on contestants farts and bait fumes. Any angler who tries to kill there fish could be tasered, handcuffed to there rod stands and drowned at high tide. This sustainable practice would provide food for the crabs, good berley and clog commercial fish nets, thus reducing catch rates and improving fish abundance..

If that seems a bit impractical alternatively a couple of ideas to improve.
Set size limit on the day based on conditions to limit unnecessary bycatch of smaller fish when conditions are good..
Encourage catch and release as a separate category of the competiion, for those who don't want there fish, by running a camera competition with a small prize say $100 for best size with camera photo.

Indicate and update by whiteboard at various points along the beach, the size of the lowest leading fish so contestants know what the standard is and can make informed decisions on whether to keep or return the fish.
And in these heady days of smart phones an app or similar is not impossible. I'm sure you could screen a picture of a whiteboard with up to date competition weights to a website for people with smart phones to log into to get updates. Very achievable for big comps I'm sure.

Think about the huge time and effort the organisers put into running these comps often with very little thanks for it from either the competitors or the public and appreciate no ones perfect but they do try bl**dy hard. Volunteers like fish are a scarce resource that also need to be looked after.