The Salmon’s Visual Apparatus.
There has been no end of speculation on salmon flies, for every angler
has his favourite patterns in which he professes to have implicit faith.
After all, these personal predilections, however strong, do not carry us
very far. They are merely individual experiences, certainly of interest,
but not founded on any scientific principle. Before assuming that the
salmon has a liking for a particular colour, it would be more scientific
to settle, if possible, whether the salmon is sensitive to colour, to
discover the range of his colour perception and the effects of the
refraction of water upon objects presented to his eye. Such an enquiry
involves the science of anatomy as well as the science of optics; but
granted an investigator adequately equipped in both departments and
endowed with a little constructive imagination, we see no reason why the
problem of the salmon’s vision should not be solved. There is no doubt
that the proper way to go about the enquiry is for the observer to
examine the salmon’s optical apparatus in comparison with man’s, to
project himself in imagination to the bed of the river and applying his
knowledge of optics to the refracting effect of water, to try to
construct a picture of any object as it would appear to the human eye
under such circumstances. When this is done it proves a very
illuminative method. The two following papers show a laudable attempt to
apply such principles, and if they do not say absolutely the last word
on the subject, they are uncommonly suggestive, and make a valuable
contribution to the solving of the problem. It is often assumed that the
salmon sees a fly merely as a dark silhouette against the sky. That is
now shown to be a very rare occurrence. He would seem to be sensitive to
colour, and under certain circumstances has a distinct sense of the
gaudiness of the lures presented to his observation.
The investigation is not without its bearing on trout-fishing, for it
brings home to the angler the conditions under which, in clear water,
the trout may behold him and his rod from the bank; it explains,
perhaps, why, in certain conditions of air and water, the fish miss the
fly, and it throws indirect light on many other mysteries that trouble
the angling mind.