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Evaluating commercial
selective fishing
C.E. AshbrookJ.F. DixonA. HoffmannK. E. RydingE. A. Schwartz J.R. SkalskiR. TownsendG.E. Vander Haegen K.W. Yi
Researchers and Technical Support
Why selective fisheries?
Harvest commingled populations and species at different rates.
• Extract hatchery fish that are produced for harvest (as mitigation for the dams).
• For the same impact on natural fish, the harvest of hatchery fish can be significantly increased.
Visual mark—adipose fin clip
• Evaluate the concept of live capture, selective harvest in a commercial fishery. Historic large return of spring chinook salmon made this possible.
• Compare conventional and experimental gear. Will the tangle net more benignly capture fish compared to the conventional gill net?
• Revise techniques; Use a revival box, shorter net, shorter soak time, and careful handling.
Evaluate four metrics: immediate survival, catch efficiency, bycatch and long-term survival.
Objectives
Gillnet and tangle net
Control and test fishing areas
Upriver
Toward Pacific Ocean
Fish Trap
Beacon Rock
Washington State
Oregon State
Evaluate condition and length
Revival box
Jaw tag on adult chinook salmon
Chinook salmon with gill and wedge marks
Chinook salmon with tangle marks
Immediate survival
53696.8Tangle (3.5&4.5)2001
83699.0Gill (8)2001
190099.15.5” Net2002126299.5Tangle (4.5)2002117298.0Tangle (4.25&4.5)2003
N
Immediate survival %
Net Type (inches)
Study year
Catch efficiency for paired nets
2001
8 inch gill net captured 2-10 times more fish than 3.5 inch tangle net.
No significant difference between 8 inch gill net and 4.5 inch tangle net.
2002
5.5 inch gill net captured 1.5 times more fish than 4.5 inch tangle net.
2003
4.5 inch gill net captured 1.3 times more fish than 4.25 inch tangle net.
Bycatch
• Mostly in tangle nets.
• Mainly shad, juvenile sturgeon, and suckers.
• Less in 2002 and 2003 through avoiding concentration areas and times.
Long term survival
63.4-94.779.116.62003 new control
55.2-81.368.213.42003 tangle
19.22003 control
46.9-66.756.811.72002 gill 5.5”
54.8-80.067.313.82002 tangle
20.42002 control
36.2-67.752.06.42001 gill 8”
62.8-10088.311.12001 tangle
12.22001 control
95%
confidence interval
Estimated
total survival (%)
Jaw tag recovery rate (%)
Group
Total survival based on Control at Bonneville Dam
100
88.3
52
67.356.8
68.2
0
20
40
60
80
100
120
control 2001 tangle 2001 8" gill 2002 tangle 2002 5.5" gill 2003 tangle
Percent survival
Gro
up
Total survival based on Control below Bonneville Dam
100 100
60.1
77.8
65.7
79.1
0
20
40
60
80
100
120
control 2001 tangle 2001 8" gill 2002 tangle 2002 5.5" gill 2003 tangle
Percent survival
Gro
up
2003—PIT tagged all adult spring chinook salmon
Jaw and PIT tag survival estimates 2003 only
13.4%
16.6%
19.2%
Jaw tag recovery
probability
Control below Bonneville Dam
Tangle net
Control at Bonneville Dam
81.5%(84.2-78.7)
79.8%(77.2-82.4)
PIT tag survival estimate
79.1%(63.4-94.7)
68.2%(55.2-81.3)
Jaw tag survival estimate
Group
79.5%
95.6%
97.6%
PIT tag detection
probability
PIT tag data by dam
Dam Tangle Control at Bonneville
Detection probability
Bonneville 855 1062 44.6%
McNary 417 497 45.6%
Three Mile 0 1 0%
Lower Granite 273 363 42.9%
Ice Harbor 290 371 43.9%
Priest Rapids 65 66 49.6%
Rock Island 32 38 45.7%
Wells 9 15 37.5%
Survival beginning at Bonneville Dam
Group N Detection probability
Ratio of probabilities
Unique treatment detections above Bonneville Dam
406 47.5% 1.04
Treatment detections at Bonneville Dam
855
Unique control detections above Bonneville Dam
486 45.8%
Control detections at Bonneville Dam
1062
Indicates that survival differences occur before fish reach Bonneville Dam
Short soaks and careful handling techniques are not enough to improve long-term survival of 8” gill net or 5.5” net captured chinook. Combined with the tangle net, they can improve long-term survival.
Long-term survival measured by releasing fish to swim freely is very different than immediate survival or net pen holding survival.
Fish in better condition at capture are more likely to survive long-term.
PIT tag post-release survival estimates are similar to jaw tag post-release survival estimates, provide tighter confidence intervals, and indicate the post-release survival differences occur before fish reach Bonneville Dam.
Conclusions
What’s Next?
Evaluate 2003 passage timing using PIT tags.
Request funds to:1. Evaluate steelhead (bycatch) survival. 2. Additional year of spring chinook study
using PIT tags.3. Evaluate spawning success.
Bonneville Power AssociationOregon Department of Fish and
Wildlife University of Idaho Cooperative Unit
Acknowledgements
2003 recapture
Of fish that were either recaptured or swam back into the net after being released, 8.5% were eventually recovered, compared to 14.1% recovery of fish that were not recaptured and did not swim back into the net.