1. Are you keeping any fish? Check the stomach contents.
2. Just catch one fish and sample the throat with a stomach pump.
Before anyone gets up in arms, I posted about stomach pumps on another BB and the following post is addressing the issue that stomach pumps kill fish. Most of the readers of my post do not know that FAOL has an article on Stomach pumps.
http://flyanglersonline.com/articles/ldy/ldy9798.php
Here is my post:
The solution is the proper use of a stomach pump, more properly called a throat pump.
Secondly, before anyone posts that we are taking food out of the fish or that stomach pumps kill fish, allow me to provide a few facts.
First to the argument that we are taking food out of the fish and robbing it of energy. The fact is that the fish uses up more of its store of energy during the fight to escape us than we take by sampling its throat. The argument that we are "robbing" the fish of food and energy is a hollow argument when made by a fly fisher whose goal is to hook a fish and fight it until it can resist no longer.
As to the argument that stomach pumps kill fish, stomach pumps have been scientifically studied and they have very low mortality. Certainly catching the fish places the fish at greater risk than a stomach pump and much greater risk than doing a shocking survey on fish. I strongly believe they are less stressful that the grip and grin photos we all take from time to time.
"Strange and Kennedy (1981) assessed the survival of salmonids subjected to stomach flushing and found no difference between stomach-flushed fish and control fish that were held for 3 to 5 nights."
Stomach pump article:
http://digitalcommons.unl.edu/cgi/vi...%20Contents%22
In the article above, the goal was to remove stomach contents. The goal of a fly fisher is to remove the throat contents which are the last few items eaten. Throat sampling is less invasive than stomach sampling.
The New Fly Fisher - Tip #28: Throat Pumps - YouTube
Tom Rosenbauer talked about stomach pumps on a podcast. I was able to track it down.
Go to the URL below for Tom's Ten Tips for Identifying and Matching the Hatch
http://hw.libsyn.com/p/b/8/9/b89c2a2...&l_mid=2597234
Tom starts discussing stomach pumps at about 20:58 into the podcast. He says, ""I'm not so sure how safe that is for trout. ?? I don't think there have been any studies done on mortality of fish that have had their stomach pumped. Probably most of them survive but you never know?.."
I have corresponded with Tom Rosenbauer after he made those comments and I sent the research on stomach pumps to him. In his podcasts since then he endorses stomach pumps and in this last podcast (8/15/14 on Steelhead), in the fly box section, he talks about his findings when stomach pumping trout. So Rosenbauer is on board with stomach pumps.
Carl Richards and Doug Swisher of Selective Trout fame used stomach pumps to gain the knowledge to write that book. Carl Richards wrote the chapter titled What Trout Eat in the The Complete Guide to Fishing with a Fly Rod published by Fly Fisherman Magazine, ISBN: 0-87165-013-4. The stomach pump is given over 3/4ths of a page coverage in picture and text on page 46. I quote from the text, "If fish are feeding underwater, two methods can be used to discover what they are feeding on. The best way is to catch a fish (usually one dummy can be taken using an attractor, fished wet, such as a Coachman) and pump his stomach with a simple stomach pump." From the caption for the pictures, "Above, a stomach designed for trout is an effective way of discovering what the fish are feeding on without harming it."
More recently, Brian Chan has also recommended "stomach" pumps as a method of safe sampling. As a Senior Fisheries Biologist, he is probably aware of the above scientific article from reviews in Fisheries Science.
Ruby Mountain Fly Fishers: Throat Pumping Trout
This is the method that I use:
Fill the pump completely water and then push out 1/2 of the water by compressing the bulb. Insert the tube gently into the throat and release the bulb so the remaining 1/2 of the bulb re-expands sucking up the food into the plastic stem. If nothing comes out, then without pulling out the tube, compress the bulb gently push in some of the water and then suck it back but don't suck material back into the bulb. Now release the trout.
The material in the tube should come out in the order that the fish ate it with the last item out being the one the fish ate last. You should not have the items into the bulb or else they will get mixed up and you won't know for sure what was eaten last. If you did suck material into the bulb, examine the food and the freshest item was probably eaten last.
I rarely pump now since I usually know what the fish are eating. However, for the beginning fly fisher it is a wonderful educational tool. A portable sampling net and the stomach pump forms the two best methods of learning what the fish are eating.
The best way IMHO to sample a fish with stomach pump is first to net the fish, no matter what it's size. Then before even taking off the hook, keep it in the net and in the water. Turn the fish upside down. This is almost always disorients the fish and keeps it from struggling. Quickly sample the fish, then drop the pump into the net, remove the hook and release the fish.
You can then examine the sample after releasing the fish. This method is the least traumatic and I have found it to be the fastest way to release the fish. It rarely takes significantly longer than most people take to just remove the hook and release the fish. It is better than lifting the fish out of the water.
Like many techniques in fly fishing, I believe using a stomach pump is what could be termed a fairness issue. Some fly fishers feel that nymphing is somehow unfair, and some nymphers think nymphing with strike indicators is less fair than fishing without. The Dry Fly vs Nymphing ethical argument originated with Halford and Skues and in some circles that argument continues to this day.
Halford and Skues: "This Chalkstream Ain't Big Enough for the Both of Us" | MidCurrent
So if you don't want to use a stomach pump, don't. But research has shown that stomach pumps are not a resource issue.
The experienced fly fisher has little need to throat pump a fish. But for a beginner, I think it is a valuable learning tool that does not harm the resource.
A throat pump is especially valuable when used in the context of fishing emergers. Emergers can be a difficult for beginners to sort out and a throat pump is one of the best tools in figuring out what is actually happening. Hence my suggestion that a throat pump is a valuable tool to study emergence.
Truth be told, the greatest threat to a trout is the most effective fly fisher because they catch the most fish. Studies have shown that hooking mortality even with barbless hooks is 3.5 - 4%. We inadvertently kill 1 of every 25 fish we catch. Catch and release 1000 fish in a season and you have killed 40 fish. I have had 50 fish days on the San Juan and two trout probably died.
This site is dedicated to educating fly fishers on how to catch more and more fish, but we do not consider this an ethical issue. Fly fishers, and I include myself, tend to forget that even C&R fishing with a fly is a blood sport.
The reality is that as we become more adept at catching fish, more fish will die regardless of how careful we are.
Regards,
Silver
"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy