During the five years that the fish trap was operated between 1996 and
<br />2000, 43,123 fish consisting of 19 different fish species (6 native and 13
<br />nonnative) and three catostomid hybrids were collected and counted. Large-bodied
<br />native fishes consistently comprised about 93% of this total for each of these
<br />5 years. Fish captures were highest in 1997 (12,233) for both native (11,547)
<br />and nonnative fishes (686), followed by 1996 (8,375), 1999 (8,264), 1998 (7,589),
<br />and 2000 (6,662). Generally, fish trap captures steadily increased in April,
<br />May, and June. Captures peaked in July and rapidly declined in August,
<br />September, and October. Total fish trap captures varied among months and among
<br />the five years of operation. For the five years, the highest fish use occurred
<br />in July and June (10,503 and 8,971, respectively,) followed by May (8,228), April
<br />(5,593), August (5,002), September (2,213), March (1,949), and October (664).
<br />Native fish used the passageway more often in June and July which
<br />corresponded with the runoff and subsequent post-runoff period in the Gunnison
<br />River. Native fish use tended to be highest in June in 1997, 1998, and 1999,
<br />although the overall 5-year total number (9,320) indicated that July was the
<br />highest month of use. Nonnative fish consistently used the passageway the most
<br />in July (1,083), followed by June (348), and August (425) between 1996 and 1999.
<br />Only in 2000 did nonnative fish use the passageway more in June rather than July.
<br />The most numerous native fish collected in the fish trap was the bl uehead sucker.
<br />The native flannelmouth sucker was the second most abundant fish collected.
<br />White sucker was the most numerous nonnative fish in the fish trap, followed by
<br />channel catfish, common carp, and black bullhead. Use of the passageway by
<br />channel catfish coincided mostly with that of Colorado pikeminnow.
<br />Surge or pulse migrations when large numbers of fish moved at one time,
<br />through the passageway were documented. Most of these fish were bluehead sucker
<br />and flannelmouth sucker. On most days preceding and following these events, no
<br />or few fish would be found in the fish trap or passageway. The highest single
<br />daily count was 1,179 in mid-April 1998 which included flannelmouth and bluehead
<br />sucker and roundtail chub.
<br />Evidence of "fallback", fishes that had passed upstream through the
<br />passageway and subsequently fell back over the dam and ascended again, was
<br />provided in 1996 by marking individuals of three non-listed, native species and
<br />three of the most common nonnative species. Flannelmouth sucker, bluehead
<br />sucker, and roundtail chub, along with three nonnative fishes that were captured
<br />in the fish trap were used. About 2%, 9%, and 5% of the three marked native
<br />fishes, three nonnative fishes, and two hybrid suckers, respectively, reascended
<br />the passageway. Thirteen (25X) of the 51 Colorado pikeminnow that passed through
<br />the passageway fell back over the Redlands Dam. Five of eight radio-tagged
<br />pikeminnow that were released upstream of Redlands Dam subsequently fell back
<br />over the dam.
<br />Recapture of three native fish species, flannelmouth sucker, bluehead
<br />sucker, and roundtail chub, that had previously been collected in the fish trap
<br />and marked, revealed that they had dispersed upstream from the Redlands Dam
<br />passageway. Some were recaptured as far upstream as 57 miles, near the base of
<br />Hartland Diversion Dam.
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