Forgive me posting this in two places. This seems like big news that would likely apply to many or most species of fish.
Scientists in Oregon were catching steelhead on flies (nice work if you can get it) in order to tag them with radio tracking devices. They were alarmed to find that many of the fish were drifting dead or unconscious a half-hour or so after release. They were able to recover fish for autopsies that showed the fish died of brain trauma or concussion. They concluded the fish injured themselves by flopping on gravel after being led into shallow water for landing. Since fish would never suffer a blow to the head in the course of normal living, their brains are not armored and cushioned the way land animals’ brains are.
It seems the same thing could happen if you let a fish flop on a boat bottom or a pier deck or an oyster bar. Ever since I learned this, I’ve found it really disturbing to watch fishing videos where a landed fish is to be released. Much of the time I’m going, “Nooooooo!”
Seems like regular use of a fish gripper could help.