8084

• UCREFRP Catalog Number: 8084
• Author: Gerhardt, D. R. and W. A. Hubert
• Title: Population Dynamics of a Lightly Exploited Channel Catfish Stock in the Powder River System, Wyoming-Montana
• USFW Year: 1991
• USFW - Doc Type: North American Journal of Fisheries Management
• Copyright Material: YES

204

GERHARDT AND HUBERT

result in 78% of the catchable fish being less than
50 cm long, and in the overall abundance of fish
longer than 30 cm declining by 75%.

Discussion
Growth of channel catfish in the Powder River
system in 1987 was almost identical to that de-
termined by Smith and Hubert (1988) in 1986,
and to that determined by McDowell (1986) for
fish from the Belle Fourche River, Wyoming, in
1985. Despite the short growing season and rela-
tively low productivity of the system, growth of
channel catfish in the Powder River system ap-
pears to be similar to that for areas with longer
growing seasons (Smith and Hubert 1988).
As in other studies conducted in Wyoming (Mc-
Dowell 1986; Smith and Hubert 1988), channel
catfish sampled from the Powder River system in
1987 were much older (as old as 21 years) than
those from other fisheries. Mean maximum age
reported for channel catfish populations outside
Wyoming was 11 years in the studies reviewed
(Sneed 1951; Marzolf 1955; Harrison 1957; Con-
der and Hoffarth 1965; Elrod 1974; Elser et al.
1977; Freeze and Tatum 1977; Hesse et al. 1982;
Paragamian 1990); the oldest fish (17 years) was
from Lake Sharpe, South Dakota (Elrod 1974).
Estimated annual mortality of channel catfish
in the Powder River system (23%) was low when
compared with that in other fisheries, where es-
timates as high as 87% have been obtained (Para-
gamian 1990). Among 26 stream sites in Iowa,
Paragam~an (1990) found total annual mortality
to range from 13 to 87% for fish 3 years old and
older; annual mortality was 23% or less for pop-
ulations at 7 sites. Hesse et al. (1982) estimated
total annual mortality of channel catfish in the
Missouri River adjacent to Nebraska to be 60%.
Natural mortality in the Powder River stock was
somewhat lower than that for channel catfish stocks
in the Des Moines and Sacramento river drainages
(both 32%). Estimated fishing mortality was much
lower in the Powder River system (1.9-2.0%) than
in the Des Moines (10%) and Sacramento (36%)
rivers (McCammon and LaFaunce 1961; Mayhew
1972). However, if our estimates were adjusted
for tag loss and failure of anglers to return tags,
the annual fishing mortality could possibly be 5-
10%. Low annual exploitation probably explains
the presence of old fish in the Powder and Belle
Fourche river systems of Wyoming.
Both the Ricker and Thompson-Bell yield mod-
els indicated that the fishery could support a 10-
fold increase in fishing mortality, to an annual rate

of22%, before a decline in yield would occur. The
Thompson-Bell model indicated that, as exploi-
tation increases, population structure and abun-
dance of fish would change considerably, with a
substantial shift toward smaller size and a 75%
reduction in fish of stock size and larger at an
annual exploitation rate of 22%. Similar shifts in
yield and population structure have been observed
in sport and commercial fisheries as the rate of
exploitation increased (Bennett 1971; McHugh
1984).
Although the fishery is lightly exploited, effects
on the sport fishery through increased harvest may
become a concern to state management agencies.
An exploitation rate of 22% annually would vir-
tually eliminate fish in the large size-classes that
attract the current anglers. A study by the Wyo-
ming Game and Fish Department indicated that
Wyoming fishermen have become less harvest ori-
ented and prefer a quality recreational experience
(Anderson et al. 1990). Catching large fish that put
up a good fight is important to Wyoming anglers.
No other sport fish are present in the Powder River
in numbers that attract anglers, and increases in
the level of exploitation could influence use. Most
of the anglers in 1987 and 1988 were local resi-
dents, who must travel considerable distances to
other fishing locations and therefore have little
opportunity to fish elsewhere. Management deci-
sions regarding future harvest, such as further ad-
vertising of the presence of many large fish in the
system, should take into account the potential ef-
fects on the quality of the channel catfish fishery.

Acknowledgments
We thank P. Eschmeyer, R. Marston, F. Rahel,
R. Wiley, and S. Canton for advice and critical
comments; L. McDonald and J. Larschied for as-
sistance with data analysis; and J. Beiswenger, B.
Diebert, B. Rhodine, R. Sanchez, and J. Smith for
help in the field and laboratory. Project funding
was from the U.S. National Marine Fisheries Ser-
vice and Wyoming Game and Fish Department.

References

Anderson, D. A., C. Phillips, and T. C. Krehbiel. 1990.
Wyoming angler attitudes and preferences; appli-
cation of strategic choice modeling. Wyoming Game
and Fish Department, Project Report, Cheyenne.
Bennett, G. W. 1971. Management oflakes and ponds,
2nd edition. Van Nostrand Reinhold, New York.
Conder, J. R., and R. Hoffarth. 1965. Growth of chan-
nel catfish, Ietalurus punctatus, and blue catfish, Ie-
talurus furcatus, in the Kentucky Lake portion of
the Tennessee River in Tennessee. Proceedings of

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