ST. PAUL, Minn. -- Your proudest fishing moment may have been when you released that trophy-size walleye instead of putting it on the wall.
You played the fish carefully, took a few pictures and gently slipped it back into the water. With an indignant flip of its tail, the walleye swam away seemingly unhurt.
Because it appeared healthy, you thought you did your part for conservation.
But did you?
Studies from across the United States have shown that a certain percentage of released fish will die after they swim away. In scientific circles, it's called "hooking mortality," and it's a fact of life in fishing.
Although hooking mortality rates vary according to species and fishing conditions, it's accepted that an average of 10 percent of all released fish die from being hooked.
"There have been numerous studies done around the country on different species, and it's surprising how often we come down to 10 percent hooking mortality," said Tim Goeman, Department of Natural Resources regional fisheries manager based in Brainerd. "The fact is, we know hooking mortality occurs."
The bodies of most fish that die of hooking mortality are not seen by anglers, Goeman said. The fish swim away from the boat and die later of internal injuries, infections or fungus. Some will settle to the bottom and decompose, while others will float to shore and be consumed by birds or raccoons, turtles or other scavengers.
In any case, the fish dies and disappears without the angler's knowledge.
The DNR conducted hooking mortality studies. One study was conducted by catching and releasing walleyes in ponds that later were drained. Anglers used Rapala artificial lures and jigs with leeches to compare the difference.
"The fish caught with artificial lures experienced 5 percent mortality, while those with live bait had mortality just under 10 percent," Goeman said. He said the survivability might have been increased slightly by the tests being done in April, when the water was cold.
Hooking mortality poses an ethical question for anglers, even highly skilled ones who practice catch and release.
If a walleye fisherman happens into good luck and catches 100 fish in a day or a few days, odds are that 10 fish died simply from being hooked. That's more than the six-fish daily limit allowed to Minnesota anglers.
Hooking mortality can increase, too, if fish are caught in deep water or released on warm days, when less oxygen is in the water. More-experienced anglers may be able to release 99 percent of their fish successfully, but less-experienced anglers might see that number drop to 85 percent, Goeman said.
"Let's say I'm the guy who caught 100 fish and released them and I'm feeling smug, but the fact is I've done more damage than the guy who caught and kept six fish and went home," Goeman said.
The 10 percent hooking mortality figure is so well-accepted that DNR biologists figure it into their models used to compute harvest on certain lakes.
Frank Schneider Jr., an avid muskie angler from St. Paul, said he often catches anglers spending too much time photographing fish or trying to subdue them before releasing them.
"I get totally disgusted with people who spend too much time playing a fish," he said. "You need to get it back into the water as quickly as possible, not hold it all day for a photograph."
Anglers who play large fish on light tackle may be endangering the fish, experts say. Prolonged struggles increase the amount of lactic acids in a fish's body, which can increase the chance of the fish dying in the days after it has been released.
Although light tackle can mean an exciting fight, it often means less survival for fish.
Anglers also often are mistaken when they assume that barbless hooks increase the survival of released fish.
Not true, Goeman said.
"There's been a lot of research done on this, including with trout fisheries out West," said Goeman. "It started to come out 10 or 15 years ago that barbless hooks didn't decrease mortality, and it was a shock to the scientific community. It makes sense to the layman that barbless hooks would be the answer, and it even makes sense to scientists, but the science doesn't bear it out.
"Barbless hooks do not reduce hooking mortality, period."
Barbless hooks accomplish one thing -- they aid the angler in removing the hook and perhaps reducing the time the angler spends holding the fish. But all things considered, the fish still fights and can sustain injuries that ultimately could kill it after its released.
Nevertheless, releasing fish -- and doing it quickly with less stress to the fish -- does more to keep a fishery healthy than killing a fish.
Most fish that are released survive to fight another day. There are many stories of fish that got away, perhaps breaking off the line, and end up being caught by another person the same day.
Goeman recalls a study he was conducting on muskies in the Mississippi River. The muskies were outfitted with special tags. One day in the fall, an angler stumbled across a deep hole in which numerous muskies were congregated.
"He caught six muskies from the hole and one of our tagged muskies twice in the same half-hour," Goeman said.
"With catch and release, the odds are still good for a fish to survive," he added. "It's conceivable there are fish out there that have been caught three or four times and will die of old age."
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