7631

• UCREFRP Catalog Number: 7631
• Author: Byrne, A. and T. C. Bjornn.
• Title: Predicting the Effect of Supplementation with Hatchery Fish on a Native Steelhead Stock - a Modeling Approach.
• USFW Year: 1991.
• USFW - Doc Type: 91-26,
• Copyright Material: NO

hatchery fish as fry (0.5, 1.0, and 3 million) or smolts
(300,000 and 700,000). Scenarios were run at two
initial native spawner escapements (250 and 2,500),
three fry fitness levels for the progeny of hatchery
parents (0.333, 0.667, and 1.0), and two mating
overlap rates (zero and 20%)--a total of 36
fry-stocking and 24 smolt-stocking simulations.
Abundance of Native Fish Declines in all
Stocking Scenarios
Although the total smolt yield was increased with
stocking, the abundance of native smolts and adults
was less than the no-stock option during generations
1-15. When native and hatchery adults interbred,
the downward trend in native smolt and adult
abundance was accelerated and the native fish were
often a minority of the total natural smolt yield and
adult return. As the mating overlap rate, fitness of
progeny with a hatchery ancestry, and the number of
planted hatchery fish increased, so did the
percentage of naturally produced fish that had a
hatchery lineage, and the danger of the native class
becoming extinct increased. The abundance of native
adults exceeded 200 fish in generation 15 in only 5 of
the 18 fry-stocking and 4 of the 12 smolt-stocking
scenarios with a 20% mating overlap rate. In the
scenarios where mating overlap was zero, a viable
native population was maintained only when
hatchery supplementation was less than 3 million fry
or 700,000 smolts.
Model can be Useful to Evaluate
Supplementation Programs
A life history model, such as the one we used, gives
managers a tool to assess the potential effects of
proposed hatchery stocking programs. The risks to
the native population can be defined and evaluated
with respect to the goals of the supplementation
program. In most scenarios, supplementation of
native stocks with hatchery fish caused replacement,
not enhancement, of native fish. Results of these
scenarios suggest that well-intentioned management
strategies to increase steelhead abundance may have
a devastating effect on the locally adapted native
stock. The long-term interaction of hatchery and
native fish in natural stream conditions needs to be
addressed.
For further information, contact:
Alan Byrne
National Fisheries Research Center
Bldg. 204, Naval Station Puget Sound
Seattle, WA 98115-5007
FTS 392-6282 or Comm. [phone]
or
Ted C. Bjorn
ID Cooperative Fish and Wildlife
Research Unit
University of Idaho
Moscow, Idaho 83843
Comm. [phone]