So much has been written on what is required to maintain healthy
populations of trout that to get into any aspect of the subject places the
reader at some risk, that of being dragged through a set of facts which he
probably already knows. Nevertheless, some things are sufficiently important
that we run a greater risk in not repeating them every now and then.
Take, for example, the role that streamside vegetation plays in support of
trout. If there is any subtlety to this topic, it may lie in the carnivorous
habit of trout, a life style that may be hard to relate, at least on first
reflection, to the flora on the bank. If trout grow fat and sassy on a diet of
insects, spiders, frogs, and other fish, what, then, has vegetation to do with
it? The answer, as it turns out, is plenty.
A substantial number of aquatic insects on which trout depend are detritus
feeders (although some, like the nymph of the dragonfly, are carnivorous).
Detritus, for the most part, consists of the partially decomposed remains of
plants. This material derives from a variety of sources -- from aquatic
plants and from streamside vegetation, the foliage of which often drops into the
Several other groups of aquatic organisms that fit into the food web,
leading eventually to trout may also feed on detritus or on the bacteria which
decompose dead plant tissues. These groups include rotifers, snails, and some
bottom-feeding fish. Removing or even reducing the normal amount of streamside
vegetation strikes a blow against trout by endangering the support base on which
trout (and other members of the stream community) depend. Paranthetically, one
of the devastating consequences of acid precipitation, in addition to
interfering with gas-exchange by gill-breathers, is to reduce the productivity
of many kinds of aquatic plants (although a few, like sphagnum moss, may
actually flourish in an acidified environment) or those growing nearby the
water system. This has a reverberating impact right on up through herbivores
reaching and extending beyond the trophic level of trout.
Another life-support role played by riparian vegetation vis-a-vis trout is
in buffering streams against detrimental runoff. As we should be aware by now,
not all run-off water reaching streams is healthy for aquatic life. Some run-off
carries high loads of silt. Silt, in sufficient volume, threatens trout by
clogging gill membranes, by burying trout eggs to depths that they die of oxygen
deficiency and by killing nymphs.
If the organic component of silt is high enough. this may raise the BOD
(biological oxygen demand) of the water through the utilization of oxygen by
bacteria and fungi which feed off the organic materials. Given high enough BOD
levels, trout will either abandon the section of the stream so affected or will
simply suffocate for lack of an adequate supply of oxygen.
If all that weren't enough, today runoff may well carry a list of other
alien compounds that are not good for trout or the aquatic ecosystem in general.
Pesticides, herbicides and other synthetic compounds do not remain on the
original sites where they are applied. Some portions reach trout streams where
they may continue to do what they were made to do -- kill living organisms.
Land-clearing and road-building may impact trout streams in a negative way
by not only increasing the silt load of those streams but also by acting as a
conduit for toxic compounds, compounds which may have been used originally for
entirely reasonable reasons, but in an entirely different context. Tests have
shown that rain or snow landing on the hardtop surface of a road will contain
measurable quantities of petroleum residues, including oils, greases and tars.
No case has been made or can be made for any of these ingredients helping trout.
If placed in streams in sufficient amounts (and the toxic threshold may be
alarmingly low), they can only be detrimental to the fish we hope to nurture and
A key word in all of this is moderation. Can man moderate his
activities so that upland and aquatic communities of plants and animals are not
threatened? His history up to this point is not unblemished, but he does have
the capacity to learn and change his ways. Some silting of streams, for
instance, is perfectly natural. Spring and early summer run-off from melting
snowbanks swells streams and increases their turbidity from melt waters
cascading down over talus slopes and bare soil. Presuming the snow is not
heavily contaminated with acid particles (not an entirely safe presumption
nowadays), this kind of process scarcely threatens stream life. Stream systems
have developed over millions of years in environments where this cyclical
process has always been a factor. Spring and summer silt is moved downstream as
the season progresses and as the frequency of rain diminishes. The streams are
given time to clean their bottoms before the cycle begins again. A wholly, (or
unholy) different kind of silting problem is presented when a major new road
is carved through the countryside or large amounts of forestlands are cleared.
These changes in the landscape create an enormous and long-term supply of silt
which may be delivered to streams in enough quantity as to overwhelm the
cleansing capacity of the aquatic system.
Streamside vegetation can retard the arrival of silt and its often toxic
components, helping to maintain of water quality.
Still a third role played by the plants associated with trout streams is that
of supplying a variety of terrestrial insects and spiders on which trout feed.
Though there is hardly a fly fisherman around who has not cursed an alder or
willow thicket for "grabbing" his or her fly, thus ruining a perfect
cast, these same individuals, queried in a more reflective moment, surely
would admit that alders, willows and other woody streamside plants are
performing a unique service. Grasshoppers, of which the Rockies have seen
quite a few these past summers, not infrequently end up in the gullet of trout
after their ungainly flight has taken them across stream only to bang into a
high-silhouetted cottonwood or willow and then to land onto the water in full
view of lurking trout. Think of the number of ants, caterpillars, beetles, and a
myriad menu of other leggy items that climb stems and branches along streams,
positioning themselves perfectly, from a trout's point of view, for delivery to
an eager clientele. All that is required is a slight misstep, a puff of wind.
or a vibrating jolt from a swaying branch) and the meal is served up.
Before another trout season is in full swing, wouldn't it be appropriate for
all lovers of trout fishing to consider the rewards of good stream stewardship?
Among those activities easiest to carry out, but with long-term benefits to all,
is the careful husbanding of our streamside plant life. Readers, individually,
or in groups, could assume responsibility for sections of specific streams.
That responsibility would begin with making surveys of bank conditions. Those
areas found to be denuded of plants or which seem vulnerable to erosion can be
targeted for restoration. Some attention to basic habitat requirements of plants
will help. In flat, sunny stretches, sedges, rushes, or willows can be
transplanted. Planting "starters" the diameter of a 2-pound coffee
can at one foot intervals could spell the difference later on in whether these
sections of bank hold up or erode materials into the stream. Along steeper
and/or shadier areas, other plants, like alders, can be established. Banks that
are in an especially bad state may require a more substantial effort including
shoring up with logs and rocks.