For many years I have fished for River Carp, which could all most be a different species.
They fight to a stand still and ofen require long recovery times.
I should say now that I dont use sacks on still waters, prefering to take a quick photo and return the fish imediately.
But on river it's completely different, having caught a carp, I keep it in the Landing net and make sure it's okay.
Then I place it in a Sack, checking the fish at intervals, making sure it's upright and facing into the river flow.
Modern weigh slings/carp sacks are good as they can be staked at both ends.
This way I'm sure when the carp is released it swims away safely.
My reason for doing this are simple, River carp fight hard, after a resting period in the landing net they may seem ready to be released.
Once released into the river they swim of appearing to be in good condition and turn belly up.
What can you do? the answer is very little, okay in the summer you may be able to recover the carp and nurse it back to good health.
But in the winter, with the river running high you dont get that option.
Many of the carp i catch are never photographed, and I only retain the fish on the grounds of safety.
It's certaintly not the sacks that are at fault, it's bad angling practice.
Bob