Abstract:
Redband trout (Oncorhynchus mykiss gairdneri) are found over a wide
range of environmental conditions and are known for their variability in life history
traits among watersheds or even within streams. Life history traits and population
structure of these trout can be influenced by a variety of anthropogenic changes
including habitat degradation and habitat fragmentation. In 1964, the construction
of Round Butte Dam created a large reservoir (Lake Billy Chinook) at the junctions
of the Crooked, Deschutes, and Metolius Rivers. It is unknown what effect the
creation of Lake Billy Chinook had on the native population structure of redband
trout in this area because no baseline data were collected before the construction of
the dam. The fate of a population of summer run of steelhead trapped above the
dam also remains unknown. This study focused on determining if Lake Billy Chinook presented a barrier to interactions among populations in the middle
Deschutes, lower Metolius, and lower Crooked Rivers by examining movement of
tagged redband trout within the system. The sub-populations of trout from the
three major tributaries of Lake Billy Chinook were also examined to determine if
they could be separated and identified based on biological characters including life
history characters, morphometric characters, and parasite faunal assemblages. The
large number of redband trout observed moving into arms other than where they
were originally tagged suggests that the reservoir does not act as a barrier to
ecological interactions among the sub-populations of redband trout in this system.
Despite some mixing observed among locations, three sub-populations of redband
trout were identified in this system. Redband trout captured in the Deschutes and
Crooked Rivers were similar in morphology and in all life history characters
examined. However, these populations could be separated based on parasite
assemblages, indicating some ecological separation. Redband trout captured
upstream in the Metolius River were morphologically unique from other
populations and can be identified most readily using simple morphological
measurements. Some differences in morphology, growth, movement patterns,
fecundity and disease and parasites suggest the possible continued existence of a
native, landlocked population of steelhead above Round Butte Dam.
