I’ve always wondered about fish mortality when catch and release is practiced.  I have seen mortality numbers ranging from a few percent to over 40%, and I worry about playing the fish too long.  I’ve also wondered about the effectiveness of barbless hooks.  Do they really help and are they worth the trouble?  I am always forgetting to crimp down the barb before casting the fly. 

I got some interesting information the other evening on these issues as I was reading Robert Behnke’s wonderful collection of articles from Trout Magazine.  Dr. Behnke, in his essay “Putting Them Back Alive” reported on some studies that were carried out  in 1964-65 by aquatic biologist Leo Marnell at Yellowstone Lake as part of his Ph. D. research.  This is perhaps the most comprehensive research ever carried out on hooking mortality of wild trout. 

In this study, many hundreds of Yellowstone cutthroat were caught using various hooks and lure types and then held for 10 or 30 days to document mortality.  Some of the results surprised me.  With all factors constant except hook and lure type, 3 of 75 (4%) of trout died after release from barbed flies, 2 of 60 (3.3%) died after being hooked with barbless flies, 3 of 113 (2.7%) on barbed treble hooks (spoon lures) and 6 of 100 (6%) on barbless treble hooks.  Statistical analysis of this data shows no significant difference between the different hook types; the differences are explained by random chance. 

A significant difference in mortality did occur with fish caught on trolled worms and released.  In this case, out of 161 fish caught, 78 (48%) died after release.  If the trout did not swallow the bait, only 8% died, while 73% died if the bait was swallowed. 

A stress test was also done.  For fish caught on a treble hook, 4 of 100 died after landing quickly, 6 of 100 died after playing for 5 minutes and 5 of 100 died after 10 minutes of playing.  So, again, there was no difference among groups that experienced different levels of exhaustion. 

The cause of mortality was detailed.  Marnell found that of the 33 deaths out of 652 trout caught on artificial flies and lures, 30 were due to the hooks causing bleeding, usually from the gills.  Only 3 deaths were from unknown causes, which might suggest lethal stress. 

Temperature is  a  much more serious concern in mortality of released trout.  A study was carried out in Heenan Lake.  Fish were caught on artificial lures during early June, mid-July and September.  Released fish were held in live boxes for four days to determine mortality.  In June and September (with water temperature ranging from 50-600 F), 1.3% of the fish died.  During the July trial, when water temperature was near 700 F, 48.5% of the fish died.  Interestingly, the highest mortality (55%) occurred with a single barbless hook.  When I was recently fishing the Williamson River, our guide, Marlon Rampy mentioned that trout that are caught in Klamath Lake are usually holding in cold areas near subterranean springs.  When they are hooked and played near the surface in the warm summertime water, their chances of survival are poor due to the stress of the warm water environment. 

This article was very interesting and answered a lot of the questions that I have been asking myself since I took up fly fishing.  I have caught a lot of fish in the past on spoons with treble hooks and always released them.  I am comforted now to know that their survival rate was just as good as the fish I catch now on tiny flies.  Maybe we should review our contempt for “hardware bubbas” with their spoons and nasty looking treble hooks.  As long as they release the fish, it looks like they are doing no more harm than we are. 

Mike Brinkley

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