Thoughts on selectivity.
I have fished, for the better part of my angling career, on the crystal clear mountain headwaters in the Limietberg reserve outside of Cape Town. These are, in many ways, typical freestone streams, containing a self sustaining population of wild, if not actually indigenous trout, with good but limited insect hatches and water that rarely gets more than a little discoloured even in the heaviest rains.
In the early years the rivers allowed for catch and kill fishing, anything over ten inches was fair game, as likely as not going to end up in a pan with some almonds. Fishing pressure was relatively low and frequently the fish’s first mistake would as likely be its last. We fished these streams with a rapid and casual style, any fly large enough to see and buoyant enough to float well in the pockets would do, size 12 Rat Faced McDougals, Humpies and Royal Wulffs were standard fare.
Presentation was limited to chucking the fly back to the same spot if we missed a take, perhaps going into a slightly more focused crouch in preparation for the hook up, which was near inevitable.. The fish would always “come again”, and of course we were masters of the art. It wasn’t uncommon to head out for the day with little more than some 5X tippet, a handful of large bushy flies and the odd weighted nymph. The nymphs were of course a last resort for unexpected high water, we were dry fly purists and only resorted to fishing “bait’ in extremis.
It was at about this time that I wrote a piece about selectivity of trout, or to be more accurate, about the lack of it, suggesting that the primary reason for a trout’s refusal to eat one’s imitation was simply a reflection on the inability of the angler to present the fly properly. We weren’t entirely without finesse, if the fish were being particularly ornery we might even change the #12 Humpy for a #14, what we thought of as “fishing fine”.
As I have commented before, if you are an outspoken and rash writer you are going to get things wrong at least some of the time and on reflection I couldn’t have been more incorrect about the subject of trout selectivity. What we had was a near wild stream with catch and kill in operation and some really pretty uneducated fish. The fishery lacking both the angling pressure and the catch and release philosophy that would in time change things around.
The proverbial “lights” started to come on with the advent of catch and release fishing in earnest, something for which myself and a few other dedicated souls campaigned rigorously. As CAR became common practice, and then in fact regulated, things started to change on the streams.
A fish that would have previously not had the chance to survive its errors now had opportunity to change its behavior based on experience and over time change they did. Those suicidal charges of gay abandon at our overly large and hardly imitative patterns started to wane, even the fish which took the flies, if missed, rarely came back for a second time and we started to worry more about leader designs, tippet diameters and actually imitating the flies on the water some of the time.
Hopper patterns, favourites for years due to their size and visibility started to work less well unless there were actually hoppers about and the rise forms of the fish changed from obvious splashy affairs to subtle glints of light on the surface of the stream. The average size of the fish grew too and it became not uncommon to find fish up to 20 inches, making languid rolling rise forms to invisible insects, ignoring our offerings (Ignoring them even if you went to the extreme of a size 14 Humpy and stretched your budget to the inclusion of some 6X tippet.) Nope the fish were getting larger, more numerous and a mite smarter and there wasn’t anything much one could do to ignore the fact. It became obvious that not only do trout have the ability to be selective, in fact I would suggest that they always are to a degree, but that they can learn to be more selective. Or at least if not learn to be so, they can modify their behavior in a manner which can only be described in human terms as “learning”, even if it is in reality some subtle evolutionary trait.
So I had to swallow some crow and admit that trout can be selective, in fact trout are selective and there is a subtle difference between the two points of view.
Firstly it seems to me that fish are by default selective. That is to say that at one end of the scale they are selective enough not to eat bananas and on the other they could be selective enough only to eat the real insects, in which case they would prove uncatchable. I am now of the opinion that all fish are selective to some degree between those two extremes and that environmental factors, such as the availability of food, angling pressure and even the sophistication of the average fishermen all contribute to where on that scale the fish’s selectivity lies at any given time.
Running the risk of applying human logic and thought processes to a cold blooded creature of perhaps limited intellect one has to try to think about what would make a fish selective and what cues it may use to decide what to eat and what to leave well alone.
For the sake of the discussion, you will forgive me if it appears that I ascribe more intelligence to the fish than I should, but I simply don’t know of a better way of describing what one can observe on the stream. So if I use the term “thought” when discussing a trout’s behavior, it doesn’t imply that they are actually thinking in human terms, but then again, as said, it doesn’t imply that they are definitely not thinking either.
So hypothetically, a trout living undisturbed in a remote stream doesn’t really have to consider much about what it eats, one would presume that early in its development it would eat stick s and stones and leaves, various items of aquatic detritus and then recognize that it lacked any real food value.
Much as small children may eat crayons or sand, the fish would come to recognize what was good to eat and what not, what provided some energy and what didn’t. The mistakes easily resolved by the simple act of spitting out the offending article until a “résumé ” of edible items was stored for future reference.
The system isn’t perfect, I still have a friend who professes to like crayons, although these days he is discerning enough to only eat the black ones.
So I believe that not only would a fish end up with a library of good things to eat but also that the fish would have some “favourites” in the same way that some of us dislike olives but will go to some effort to get hold of smoked salmon for example.
One only has to witness the wayward and out of character manner in which some trout approach the limited calorific value of an ant to realize that they actually seem to particularly “like” some foods more than others.
So our hypothetical fish, growing up will do well to try different things, avoid predators and get on with the business of growing larger, its dining unsullied by the interruption of an anglers imitations to confuse the issue.
Enter the angler, (one may well say “tutor”), his less than perfect imitations are taken in by the fish, but the problem is that they are no longer as easily spat out should they prove unpalatable. In catch and kill waters, now for the first time, the fish no longer enjoys the safety of making a reversible error, one mistake and its all over with no chance to “learn” from its mistakes..
Still some fish will be hooked and lost, the larger fish and therefore ,in a wild environment by default the older fish, will have survived such encounters with anglers and their imitations and will prove more difficult to fool. Again this is standard angling folk law, the larger the fish the more difficult to catch, (except for those which are stocked large and where their size is no longer an indication of their relative experience and sophistication).
It would seem then that on a regularly fished catch and kill water most of the fish will not have the opportunity to learn and the rare few will become more tricky to fool as a product of experience, should they be fortunate enough to escape capital punishment for their early mistakes. Now when our hypothetical trout stream enters the realm of controlled catch and release, (something of which I am still a firm advocate it must be said), the fish get to make mistakes without inducing their immediate demise and therefore have at least the opportunity to “learn from their mistakes”.
It would seem logical that in this environment they would start to modify their behavior based on what is good or not good to eat, apparently edible food forms which result in a hook in the nose and the waste of a lot of energy running about trying to escape are likely to be avoided and over time a repertoire of signals that warn that certain “food items” might be suspect must surely accumulate in the same way as a repertoire of what is good to eat does..
Back to our example of disliking olives, you may eat the first one because it looks nice and other people are eating them, you may even try again assuming that perhaps the first one you had wasn’t a particularly good olive after all. But if you find that you strongly dislike the taste the second or third time you will eventually select not to consume them. The oval shape, olive colouration and the red pimento in the middle are all cues to you that it isn’t something that you want to eat and you will avoid them..
So it is , I am sure, the same with trout, they eventually build a repertoire of what is good to eat and what not and a variety of signals or cues which help them make that decision.. knowing what you can safely eat, must by default be a natural response for all animals on the planet if they are to survive. So I suppose that it behooves the angler to try to get some idea of what cues fish use to identify food and which cues might alert them to the idea that not all is well. I will discuss this further in a later post.