Upload
others
View
7
Download
0
Embed Size (px)
Citation preview
Coastal Cutthroat trout Shoal Spawning in a high montane lake of
the Cascade Range of Oregon
David Saiget
Mt. Hood National Forest
Zigzag Ranger District
Bull Run Reserve established in 1895 which closed public access in the Bull Run Watershed which serves as the drinking water supply for Portland metro area
4.2 mile circumference - 486 ac
natural lake level fluctuation 12’/year
As the headwater source for Portland-metro area drinking water, lake drawdown can occur in times of high water need which may have an affect on the fish population
Objectives:-determine extent of shoal spawning
-collect spawner, redd, and fry counts
-observe shoal spawning behavior
low avg high (n=5)
050
100150200250300350400
# of Eggs in excavated tributary redds
Avg length of females 14-18 inches
03-May07-May
11-May14-May
18-May21-May
24-May28-May
01-Jun05-Jun
09-Jun13-Jun
01020304050607080
Num
bers
N. Point & boat rampEast Isle
Snag Patch SW corner 4A shoal
Shoal spawner counts, 2003
05
101520253035
No.
Fry
Experimental gravel Natural Road/pit run
Fry production by substrate type
2.5 3.7 4.2 4.3 4.9 5.1 5.5 6 6.2 6.3 6.4 6.8 8.5 9
Depth, feet
05
10152025
3035
Fry production by Water depth
07-M
ay12
-May
17-M
ay20
-May
24-M
ay29
-May
03-Ju
n08
-Jun
13-Ju
n18
-Jun
23-Ju
n28
-Jun
03-Ju
l08
-Jul
13-Ju
l18
-Jul
23-Ju
l28
-Jul
5
10
15
20
LakeTrib 4A
shoal ht of spawntrib ht of spawn
Shoal emergence Trib emergence
Lake vs. tributary water temperature
1st redds observed 1st fry observed
Conclusions
Warmer temperatures and earlier emergence
may represent an advantage for shoal fry over tributary fry in the early growth stages
Limited spawning habitat in the tributaries may drive spawning in the shoals
Changes in lake surface elevation which prevent tributary accessmay force spawners to utilize the shoals
Shoal and tributary spawning may represent two divergent life histories
Absence of up- or down -welling, low DO’s, or poor substrates may be limiting fry production in shoal areas
Low productivity, oligotrophic nature of the lake may have in effect changed shoal spawning opportunities into feedingopportunities for many of these fish
Despite the high predation of eggs and less than optimal substrates, the presence of emergent fry in the shoal areas suggests that spawning in the shoals is a successful life history adaptation
Funded by:
Mt. Hood National Forest
Zigzag Ranger District
City of Portland Water Bureau
1992 1994 1995 199510001300160019002200250028003100340037004000
Population Estimates from hydroacoustics