"There are some other ways to avoid catching fish. Looking good out there can definitely be a handicap. White hats and shirts, flashy rod finishes, gleaming rod jewelry, and bright metal fly reels are all big sellers among fashionable fly fishers, but they are reliable trout spookers. Combine such high visibility with any sudden movement, such as false casting and it's "Hasta la vista, Mister Trout." Bob Wyatt - What Trout Want -The Educated Trout And Other Myths
The practice of using a stomach pump seemed to rear it's head about 30 to 40 years ago, stuck around for a while, then sank without a trace. Now it seems to be re-emerging, a pseudo scientific exercise used to reinforce debunked theories and impress others. It's also harmful to trout.
We know the drill: "If done properly stomach pumping is safe and not harmful to the trout" the saying goes. The words If done properly are key here. Just because the trout is caught, admired, photographed, then pumped and released and swims away does not mean that harm has not been done. A safe release may be the case for trained fisheries personnel but not for your average untrained, ham handed Joe. (years ago, while working at a private trout hatchery, I assisted with egg stripping under the watchful eye of the hatchery manager. We were very careful and egg stripping is a lot less invasive than stomach pumping!!)
Injury to trout - Abrade the esophageal membrane of a trout and that trout isn't going to have a sore throat for a day. It's going to die and you will not even know it because it will swim away but will not be able to feed. "That doesn't happen to MY fish" the story goes but HOW DO YOU KNOW THAT? The answer is you don't! The answer may have been found on the bottom of the Tree Pool last Sunday (2 dead trout) and down through the top of Cady Lane (over a dozen since August). These fish were played out, photographed while lying on wet rocks and then lovingly released and then never recovered. Chances are they were not pumped but it is reasonable to assume that pumping may have happened and that would add to the mortality rate. Gastric Lavage (pumping) has been used by trained fisheries people and in one study done in British Columbia all fish were anaesthetized before getting pumped. Hmm....Why is that??
How Much Food - According to the late Robert Behnke, considered by most to be the world's best authority concerning trout and salmon, a one ounce trout (approximately 30 grams) would need 1 gram of food daily to not only maintain size but to also promote growth (approximately 3.3% of body weight consumed daily). A one pound trout (453 grams) would need to consume approximately 15 grams of food daily to survive. Now, this doesn't sound like a lot but when the available prey (aquatic insects) are weighted in milligrams (1000 milligrams in a gram) it comprises a vast number of insects especially in rivers like the Swift. What is pumped out could of taken hours to consume. We make the trout start all over again!!!
"I get to know what the trout are feeding on and can use the right fly" is the stale truism that props up this quackery. "Match the Hatch" followers and those who actually believe that trout are selective can be pom-pom wavers for stomach pumping. (Please read Wyatt's book quoted at the top before you contact me concerning selective trout).
Last June I did a video on the Swift. I caught a LOT of trout in that hour and almost all of them were packed to the gills with sulphur nymphs. All I had to do was look inside their mouths and see many nymphs that had not even been swallowed. Was I using a sulphur nymph as the hatch match folks preach? No. I used a size 14 partridge and olive which imitates the prey form seen in many aquatic insects. No need to take out the turkey baster!! You'll find plenty of size 28 stuff if you bother to look inside a trout's mouth too!
In short, if you care about releasing trout with the least amount of harm done then dump the plunger and become an observer. Look at what's in the air, on the water and on the shore. Know your seasons and what each brings to us in the way of insects. You will probably be able to predict what the trout has been eating without pumping. Start with the fly on your line if you want a clue!!