City Creek Nature Notes – Salt Lake City

November 12, 2016

November 12th

Filed under: Brown Trout, Fish, Flood retention pond, Stream, Water Treatment Plant — canopus56 @ 3:23 pm

Trout Vision

10:30 a.m. On this warm weekend day, the canyon is again full with twenty to thirty people, and I stop at picnic site 6 to look at the trout in the stream pool (Oct. 21st, Nov. 4th, Nov. 10th). Today, there is a large brown trout in the middle of the pool facing away from me. The line of sight from his nose to my position subtends 150 degrees. Nonetheless, the trout immediately spots me and bolts for cover. Thomason explains that trout not only have color vision, but they also have a 180 degree field of lateral vision, 10 degrees of which is forward-looking over-lapping binocular vision (id. 184-187). The trout can see 170 degrees on each of its sides, and has only a blind-spot around its tail. This is why the smart trout in the pool today apparently, like your mother, has eyes in the back of its head. But its vision for distant objects is poor, and for far objects, it can only see moving shapes. The true size of those shapes are also distorted by the refracting property of the stream’s surface. The trout’s eye is remarkably different from our own. The human eye is egg-shaped and we focus by using muscles to distort the eye’s lens. The trout’s eye is a circular affair with a circular lens, and it focuses by using muscles to move the entire lens backwards or forwards. This also allows the trout to see nearby objects in great detail. Thus, the trout’s vision is well-adapted to its needs. It has a wide field-of-vision necessary to quickly avoid predators, good close vision to identify both nearby water-dwelling insects and land-insects that have fallen into the water, and narrow forward-looking binocular vision to direct the final strike on its insect prey.

A man-made obstacle prevents the trout to moving above the flood retention ponds at mile 3.1 (Sept. 10th). There a sluice gate prevents their travel upstream into the remaining 11 miles of canyon stream. Perhaps there is some reason for this, i.e. – the need to protect machinery at the water treatment plant or the desire to have the highest quality water above the plant’s intake by banning defecating trout. But I cannot imagine that the trout would generate any more bacteria than the hapless insects who drown in the stream and on whom the trout feed. The sluice gate could be easily modified to allow the trout into the upper reaches of the canyon. It is a simple concrete box about thirty feet long across which water moves spread out at a depth of about 1 inch. One-half the sluice ramp could be changed into a series of steps and pools that the trout could easily traverse. I forward my idea for a fish ladder at the sluice gate to the City through one of its many websites (Nov. 10th), but I expect no reply. Such governmental websites are meant only to provide the appearance of responsiveness to citizens. No one actually reads or replies to them, and if a reply is received, it is usually a well-written note by a communications major who does not know anything about the topic, who has no power of decision-making, and who is practiced at deterring citizen involvement with a template response stating that of course nothing can be done.


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