Oh curious brook trout
Appearing unexpected
In the mainstem ‘T’
Throughout our surveys, fishing provided an interesting glimpse of what lay lurking in the currents. As with most field studies, there were some surprises, and one jaw dropping discovery. The jaw dropper came on our first week of study on the North Fork Tuolumne confluence. The famous angler, Carson, caught a brook trout on mainstem Tuolumne. That may not sound exceptionally surprising; particularly if you are not an angler or a fish enthusiast, (two other trout species are present in the Tuolumne, why not a third?).
Brook trout (Salvelinus fontinalis) are a char native to the eastern coast North America, and have been introduced across the continent as game fish species. Brook trout are excellent eating and are very willing to strike artificial lures, making them very desirable if you are a fisherman. In addition, their sporting qualities, brook trout also have the strictest water quality requirements of any trout in California. Brook trout inhabit the coldest and cleanest waters in the state and fair poorly anywhere else. Though they are the only California trout capable of feeding at one degree Celsius and readily out compete other trout (namely brown, rainbow and cutthroat) in high elevation headwater streams, they rapidly loose their competitive advantages when average annual rise even a few degrees (Moyle 2002).
The middle reaches of the Tuolumne are hardily prime habitat for such a coldwater fish: summer temperatures reach over 20 C and winter lows rarely fall below 5 C. Due their physiology, brook trout spawn at times when flows are most likely to be high. This reduces their chances for high recruitment rates (Moyle 2002). Even the famed brown trout, which enjoys competitive superiority over other trout, cannot achieve dominance in the Tuolumne because of similar recruitment limitations. A poor competitor at warm temperatures, brook would not be able to persist in the face of such circumstances.
The brook trout Carson found in the Tuolumne is not likely to have originated in the Lumsden reach or any of the immediately adjacent tributaries. Ultimately the journey to the Tuolumne must have been interesting for the fish. This road to the Tuolumne could have started in the Clavey tributaries, which support self sustaining brook trout populations.