9647

• UCREFRP Catalog Number: 9647
• Author: Wydoski, R. S.
• Title: Fish Population Manipulation.
• USFW Year: 1990.
• USFW - Doc Type: Denver.
• Copyright Material: NO

Case Histories usinq Gill Nets
A program of netting was used to remove the large population of longnose
suckers which were believed to adversely affect angling returns of rainbow
trout in Pyramid Lake, Alberta since stomach analysis indicated competition
for food (Rawson and Elsey, 1960). During a seven year program, 27,597
longnose suckers were removed; 2/3 by gill nets and 1/3 in wire-mesh traps.
The age composition of the sucker population was drastically changed from 14
age groups at the start of the program to 8 age groups at the end. It was
concluded that the reduction in the longnose sucker population has not
improved the game fishery for rainbow trout. NOTE: Compensatory changes in
fish populations following reduction in numbers may result so that the end
result is negligible unless a large proportion of the population is removed.
In another case, predation on sockeye salmon during the early life was
believed to be significant in reducing the survival before smoltification
(Foerstaer and Ricker, 1941). Predatory fish in order of importance were the
northern squawfish, Dolly Varden, trout, and coho salmon. Gill netting,
supplemented by seining, bait lines, and cage traps, between 1932 and 1938
captured 20,047 fish including 10,130 squawfish, 2300 trout, 700 char, and 720
coho salmon. Squawfish and char over 200 mm were reduced to one tenth of
their original abundance. The changes in survival rate of young sockeye
before (3.13) and after (9.95) the netting operation were significant. It was
estimated that 3,800,000 smolts were saved by the reduction of the predators.
Seining proved to be successful in a 1,600 acre Indiana lake with an average
depth of 10 feet and several good hauling beaches, (Ricker and Gottschalk.,
1941). The seines were between 800 and 1000 feet long and 8 to 20 feet deep.
The following species were removed; 12,281 carp (45 tons), 14,456 quillback,
1,441 buffalo, 65 suckers, and 215 gar pike. Removal of the fish was followed
by a clearing of the water, increased rooted vegetation, and better angling.
However, subsequent attempts at seining other lakes failed that was attributed
to either a scarcity of good seining beaches or inability to catch enough
fish.
Case History of Traps and Trawls
From 1955 through 1966, 35.5 million pounds of commercial fish were removed
from Lake Winnebago, Wisconsin (Piregel, 1971). Of this total, 33.4 million
pounds were freshwater drum. Fluctuations in freshwater drum harvest have
been governed by abundance and fishing effort, primarily with trap nets and
trawls. The freshwater drum removal program was considered successful on two
accounts. By removing the freshwater drum, a species considered undesirable
by the sport angler, more space for desired sport fish has been provided in
the lake. Lake Winnabago has always been known for its walleye, sauger, and
white bass fisheries. When the removal program began, these fish populations
increased and the yellow perch and black crappie fisheries also flourished.
The commercial harvest of freshwater drum has had no detrimental effect on any
game or panfish species. In addition, 34.3 million pounds of drum were
removed from 1955-1966 with a commercial value of $1.01 million that would
have otherwise been wasted. Through an Information and Education program„ the
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