8097

• UCREFRP Catalog Number: 8097
• Author: American Fisheries Society.
• Title: Proceedings of the 18th Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
• USFW Year: 1983.
• USFW - Doc Type: March 2-3, 1983.
• Copyright Material: NO

Table 1. Lengths and weights of aged brown trout.
Age 1 2 3 4 5 6 7
L (rom) 240 303 334 395 465 560 570
1979 W (g) 170 297 365 640 945 1911 2052
No. 2 40 86 65 40 11 3
L (rom 147 234 318 337 445 562
1980 W (g) 169 333 405 1077 2013
No. 7 19 61 23 7 2

Average lengths and weights for all fish collected declined during the 2-year
study (independent t-test, P < 0.001). Mean lengths in 1979 and 1980 were
420 mrn and 347 mrn, respectively; mean weights in 1979 and 1980 were 788 g
and 443 g, respectively. The length-weight relationships of brown trout in
1979 and 1980 were very similar (Davis 1982).
Condition factors were plotted against age and length (Figs. 3 and 4) .
Condition decreased between the ages of 2 and 4, then began to increase as
the fish aged. Condition also decreased for brown trout less than 400 rom
TL, then increased for brown trout over 400 mrn TL.
Growth seems to have been slowest for brown trout 3 and 4 years of
age and fastest for fish 5 and 6 years of age (Table 2).

Table 2. Average length and weight increases of aged brown trout, 1979-1980.
Year Class Age L (rom) W (g)
1977 3 15 36
1976 4 3 40
1975 5 50 437
1974 6 97 1129

Female brown trout outnumbered males in the 1979 and 1980 spawning
migrations (Table 3). This could be due to differential post spawning sur-
vival between males and females. Jonssen and Stenseth (1977) theorized
that females have a greater chance of survival than males because they
mature a year later at a larger size.

Table 3. The sex ratio of female to male brown trout in the 1979 and 1980
spawning migrations.

1979

1980

No.

%

No.

%

F
M

483
307

61
39

288
194

60
40

40