I fish Northern NSW beaches and fish one particular beach, have done so for over 20 years.
On this beach last week the netters hauled 16 tonne of mullet. The mullet had not spawned.
This beach then shut down completely, no dart, whiting, or tailor in gutters . Conditions were there and the gutters were there for fish but nothing.
After about a week a school of baitfish moved in travelling north. There was no predatory fish ie. dart tailor.
Fishing at night in the same gutter produced one small chopper tailor in a 3 hour session.
I have 2 points:
1. Removing 16 tonne of mullet before spawning has to have a huge effect on the marine enviroment as far as the food chain goes.
2. Beach netting does shut down the fishing on the beach.
I cannot comment on the distance but from experience 1-2 klms either side of the netting area shuts down.
This is experience, a study would be easy to prove just by anglers fishing the beach after netting.
Furthemore after 20 years of fishing the same beach the fishing is getting worse.
Please do not say this is because of recreational anglers as in my experience only a small number actually catch a lot of fish.
And before I get jumped on, I fish for fun and only keep a small quantity of fish.