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

Pacific Coast fish from the San Joaquin Delta averaged about 120
mm in annual growth increment for the first three years, 60-70 mm
between ages 4 and 6, and 50 mm annually after age 8 (Setzler et
ale 1980). Lake Powell fish grew faster than ocean fish prior to
maturity and slower following maturity. The broad range of types
and sizes of forage available to ocean fish explain these
differences.
Table 3 depicts the growth history of Lake Powell striped
bass in 5 year blocks. The 1975-1979 block showed maximum
growth. Natural reproduction, beginning in 1979, resulted in a
geometric increase in striped bass numbers. Growth decreased
slightly due to intraspecific competition during this period
(1980-1984) but was only 30 mm less for 4 year old fish. Many
individuals obtained large size, and reached ages of up to 10
years. These larger striped bass had a mouth gape size large
enough to consume one-pound carp which became a staple in their
diet. Most of these large fish attained lengths >600 mm before
shad numbers declined and continued to grow after switching to a
carp diet. Growth of younger striped bass diminished as shad
numbers declined.
The period 1985-1989 marked a dramatic decrease in growth
rates as striped bass numbers peaked, and shad were eliminated
from open water zones by intense predation. Total back-
calculated length at each age class dropped 100-225 mm less than
previously seen in 1975-1979 (Table 3). Striped bass were
shorter, did not live as long, and some never obtained sexual
maturity. Most of the population was composed of immature fish
300-400 mm TL which were as young as Age 2 or as old as Age 6.
Stunted striped bass resorted to eating plankton in the pelagic
zone after the annual crop of shad was consumed soon after
hatching.
Slow growth and small size of striped bass (1985-1990)
allowed the largest (>150 mm) shad to escape predation and
produce measurable shad year classes in 1990 and 1991. Striped
bass growth gradually recovered during the period 1990-1997 as

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