1. Recent investigations on the Watauga River and South Fork of the Holston River documented natural reproduction by brown trout Salmo trutta; no reproduction was observed in the Clinch River or Hiwassee River. This two-year study was undertaken in 1998 to document the extent of spawning activity in these four east Tennessee tailwaters and to describe factors limiting reproduction by brown trout. Wild age-0 rainbow trout were also observed in three of these tailwaters, but because of low abundance, the spawning ecology of rainbow trout was not examined in this study.
2. Redd surveys were performed on each tailwater to document
spawning effort, and spawning substrates were quantitatively examined using the
pebble-count technique. The fecundity of brown trout in each tailwater was
also measured and compared.
3. Spawning was most prevalent in the South Fork of the
Holston River and occurred, to a lesser degree, in the Watauga River. In
general, spawning substrate was poor at most sites in all rivers and armored
substrates were prevalent. Redd construction was often attempted in
sediments too large for trout to move, resulting in failed nests. In some
locations, particularly in the Clinch River and South Fork of the Holston River,
redds were constructed but later destroyed by high discharges resulting from
hydropower generation.
4. Fecundity of brown trout was significantly lower in the
Hiwassee River; trout fecundities in the other three rivers were statistically
similar and comparable to brown trout fecundities in other U.S. rivers.
The poor reproductive fitness of Hiwassee River brown trout was probably linked
to elevated water temperatures each summer (approaching 24oC) and low
water fertility as measured by alkalinity (9-12 mg/L as CaCO3).
5. Over 30% of female brown trout collected from the Hiwassee
River and the Clinch River contained atretic or unused ova, compared to only 5%
of trout from the Watauga River and South Fork of the Holston River, which
indicates that many mature trout were not attempting to spawn in the Clinch and
Hiwassee Rivers.
6. Redd construction activity was monitored weekly at five
sites on the South Fork of the Holston River during the 1999-2000 spawning
season. Redds were first detected on 6 November 1999, although peak redd
construction did not occur until late December 1999, when water temperatures
fell below 10oC. No new redds were observed after late January
2000. Mean depth (at base flow) of brown trout redds in the South Fork of
the Holston River (n = 105) was 24 cm.
7. Coupled with poor substrate, extended periods of dam
discharge above base flow during the spawning season were probably responsible
for the lack of reproduction by brown trout in the Clinch River. Brown
trout reproduction in the Hiwassee River was hampered by the lack of suitable
spawning substrate, extended periods of high flow during the winter spawning
season, and poor adult fitness. Although adult fitness was good in the
Watauga River, and suitable flows and water depths were sometimes present during
the spawning season, spawning substrate was very scarce in that tailwater.
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