Just how do Trout eat their prey? Does this knowledge help us catch more fish?
It was a perfect night for fishing the rip. The current formed by streams or rivers entering, out into a lake. Pitch black and windless. There were large shoals of smelt in the water. Plenty of trout feeding too. Their splashing testifying to what we could not see.
Five or more of us, (seeing more than a man away was impossible), were flinging flies in the general direction of the sounds but none of us could achieve a hook-up.
For about the fifth time in an hour I felt a pluck on the line - I struck - but nothing. Again I stripped in the line to check the fly, a soft silicone number. For the fifth time I needed to replace it – the tail section gone again – the body section serrated by teeth marks.
"Damn pluckers," I hissed to the night.
"Yea," answered one of my shadowy companions, "they are just nipping at the flies."
General agreement rolled along the line of anglers.
The night continued that way. The casting irregularly interrupted by a "damn" or stronger, as the ‘nippers’ and ‘pluckers’ toyed with us.
I fished on, thinking about a couple of articles I had read. One in an English trout fishing magazine about a year before. The English article was written by a doyen of the U.K. fishing scene.
A proper fishing gent he is too – from the tweed coat to the tie he wears - while fishing!
The tone of the article closely matched this gentleman’s appearance – patronising to a nauseating extreme.
The article commenced with this little example of down my snobbish-nose drivel; "When I am fishing and I hear fellow anglers saying how hard it is to hook-up because they are just plucking at the tail of the fly, I smile and think to myself how little they know."
The writer went on for 3500 words to explain that trout do not ‘pluck at the tail’ because that is not the way they feed.
The writer theorised that trout engulf their prey. That is, trout approach their prey, open their mouths and flare their gills, and the prey is sucked in to the mouth.
O.K. so for the moment we accept this theory, but if it is true how does he explain the ‘nipping’ and ‘plucking.’
The tweed coated gent's theory was that this occurred because the fly is attached to a line and many times while being retrieved the line is relatively taunt to the fly. So when the trout approaches, opens its mouth and flares its gills the fly cannot be drawn into the mouth. So it only briefly catches the lip.
When I first read the English version of this theory my first reaction was, in English slang – ‘bollocks!.’ That reaction may well have been an adverse reaction to the patronising - "I know better than you" - tone of the article. However, even after reading the article again I remained unconvinced of the theory.
My skepticism was based on my own observations, and the fact that the English writer based much of his observation of trout feeding habits in hatcheries.
So how do trout feed? I delved into my own fishing book library, the public library, and searched the Internet. How much information did I get? Very little indeed. There are literally thousands of books on what, where and when trout feed, but very little that I could find on how trout feed.
What information I could find confirmed that trout do feed by ‘engulfing’ their prey, but not as our posh patronising theorist would have it, exclusively.
When trout are feeding on drifting or very slow moving prey, nymphs, shrimps, very small fish, and flies on the surface, engulfing is used almost exclusively.
The prey is approached or carried by the current in front of the trout which opens its mouth, flaring its gills and so sucking the prey into the mouth. The prey is trapped by the tongue against the roof of the mouth to ‘test’ the food, and then either swallowed or expelled.
This whole process takes place very quickly, almost in the blink of a figurative eye.
Feeding this way is not exclusive to trout. Many saltwater predator fish use similar techniques. For instance snapper, kingfish, bass and hapuku (groper) feed this way as well. But again not exclusively.
Some prey is not engulfed.
To engulf some prey would pose a very real life-threat to the fish. Freshwater crayfish must be grasped and turned tail-first toward the throat and then swallowed, otherwise the spikes and spines could catch in the throat and choke the fish. This is also true of larger-baitfish prey with spikes and spines.
This grasping feeding system is confirmed by the fact that trout have small, sharp grasping teeth. Nature simply does not equip animals with appendages they do not need, especially fish that have been around as long as trout.
So what about the observed 'evidence' of hatchery fish made much of by the tweed suited one.
Fill a tank with hundreds of small trout and throw in some feed pellets and a frenzy occurs. These fish dash about engulfing everything that falls through the water. Let these fish grow on, and release them into a lake and what happens? Very interesting. The English stocked still-water fisheries provide interesting trends.
In this scene a fixed number of fish are released every evening after fishing has closed for the day. Next day fishermen pay to fish for them. In most of these waters using fish-feed pellet imitations is not allowed.
The operators of these fisheries work on the basis that over ninety percent of the fish released the night before will be caught the next day. Despite the fact that no pellet imitations can be used. Seems that just about anything that falls through the water will be eaten by the trout. 'Conditioned behaviour' is the word, (actually 'words' as you have already observed).
The primary point here is that observation of hatchery fish feeding behaviour will not and cannot provide any real basis for a hypothesis on those fishes’ natural behaviour in the wild.
In a hatchery there is only one source of food. That source of food is delivered in the same way every day, usually at the same time. Competition for that food is intense.
So observation in the wild should provide the most telling clues. Here is what I have observed.
Trout will delicately pluck nymphs from weed in lakes, even in heavily weeded lakes. I have observed them swimming along the edges of weed banks nipping nymphs, worms and snails off the weed as they go.
As some kind of proof that these fish are not engulfing the prey is the fact that any of these fish that I have caught, have little or no weed in their stomachs.
In deeper water, trout chasing smelt regularly ‘ball up’ small schools of smelt then swim around it picking off one at a time. Sometimes when this is happening on the surface, fish can be observed with prey in their jaws.
(See "Fishing in a Goldfish Bowl' - for more information on the 'balling-up' tactic)
In shallow water around lake edges I have seen trout move onto a smelt imitation fly and ‘nip’ at it and immediately let go. I have learnt that sometimes if the retrieve is stopped immediately this happens the trout will move forward and pick up the fly as is drops.
Then there is the evidence that started this story - the silicone flies with missing tails and teeth cuts on the body. The engulf, swallow or expel theory does not cover this. These flies have been bitten.
There was one fisherman who caught fish that night, and he was using silicone flies. We stopped fishing at the same time and as we walked out of the water I asked him what he was doing.
Seemed his technique involved not striking if the fly was nipped or plucked.
Instead he dropped the rod tip and immediately flicked some slack into the water. This allowed the fly to sink. Often he got a hook-up almost immediately.
In addition every time this technique worked, when he landed the fish the fly was always without its tail.
I could have left it at that, but I noticed as we walked up the bank and into the light that the silicone fly he was using was very big by usual standards, perhaps 50 to 60 mm long, compared to the more usual 30 to 40 mm long.
I have no scientific evidence but there does appear to be two versions of smelt in Lake Taupo, one of which is significantly larger than the other. It seems to me that when I observe shoals of the larger smelt in the water, nipping and plucking becomes more of a problem.
Maybe the feeding technique is different
depending on the size of the prey?
Then a few weeks ago I saw a brown trout chasing a small rainbow in the shallows and I got my final clue.
The brown did not try to engulf the rainbow, instead it seemed to try and get just alongside the rear of the fish, and then with a rapid swing of its head, it snapped its jaws. After two misses it finally caught the rainbow.
So I started to watch rainbows in shallow clear-water chasing my flies. Same thing.
The rainbows swam slightly to one side of the fly, and then swung its head across and grasped the fly. This, in a bay where larger smelt seem to predominate.
On a couple of occasions I have been lucky enough to observe a rainbow at close quarters in clear shallow water harrying a shoal of smelt. On both occasions the trout slashed around and through the shoal snapping and nipping at fish. When the shoal broke up the trout leisurely swam back through the area picking up wounded fish.
Why do they appear to behave this way?
Very simple really. Trout like many other predator fish cannot see what is directly in front and close to its snout. When their mouth is open this becomes even more true. So for larger stronger prey that may well be able to resist a trout’s limited engulfing ability in still water, the biting tactic may be required.
Trout have existed on this planet for millennia, and like sharks they have not changed very much over that period.
Lack of change in nature usually means one thing, that an animal is ideally suited to its environment. Trout will feed on a variety of prey, in a variety of water during its life span.
I contend that they do not use one method of feeding, and while it may be true that trout mostly engulf their prey, there are times when they bite and grasp, before swallowing, especially in lakes.
So the next time you feel a nip or pluck, ignore the smarmy, patronising smile of the English writer, and disregard what he would have you believe he knows, and immediately stop your retrieve and let the fly sink. If you hook up then it may not prove the engulfing theorists wrong and me right, but hey, it may well get you the fish.
Article written by Tony Bishop