9368

• UCREFRP Catalog Number: 9368
• Author: Gustaveson, W. A.
• Title: Cyclical Population Dynamics of Self-sustaining Striped Bass in Lake Powell, Utah-Arizona, 1974-1998.
• USFW Year: 1999.
• USFW - Doc Type: Salt Lake City.
• Copyright Material: NO

Fish with K factors less than 1.0 have deteriorating flesh and
less desirable fillets.
Striped bass condition mirrored shad abundance (Figure 2).
The initial, expanding striped bass population (1975-1981) was
consistently healthy with K factors near 1.3 despite some
cyclical swings in shad abundance. Prior to striped bass
establishment shad exhibited a population peak every third year
with two moderate production years in between. Shad peaks in
1981 and 1984 allowed high survival of striped bass year-classes
which subsequently placed tremendous predatory pressure on shad
in succeeding years. Condition of adult striped bass declined in
1982 and 1985-1989 to levels where harvested fish were
unacceptable to anglers.
Juvenile striped bass were able to maintain better condition
than adults by foraging on plankton if needed. Juvenile striped
bass occupied the same niche as YOY shad in the warm epilimnion
and eliminated shad forage from the pelagic zone in years when
juvenile striped bass were numerous. Adult striped bass required
cooler temperatures and were forced deeper in the stratified
reservoir (Schaich 1979). The ontogenetic separation of
different sizes of striped bass favored juvenile fish at the
expense of adults because juveniles could reside in the same warm
water zone as their prey. This juvenile-dominated imbalance in
the striped bass population continued through the 1980's.
High striped bass numbers combined with drought conditions
to keep the shad population low. From 1985-1990 there was no
detectable shad population in open water when sampled with
midwater trawl. Adult shad found thermal sanctuaries from
striped bass in shallow, turbid water in the backs of the coves.
Shad venturing into open water were vulnerable to predation. The
end result was a stunted striped bass population that did not
grow to maturity. Adult shad too large to be consumed by stunted
striped bass were stockpiled in thermal sanctuaries until
conditions were finally right for a shad population recovery. A
good shad spawn in 1990 resulted in a population large enough to

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