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Using PIT tags to evaluate the post-release survival of spring chinook salmon following their release from commercial nets
C. E. Ashbrook, J. R. Skalski, K.W.Yi, R. Townsend, J.F. Dixon, and E. Schwartz
Image provided with permission by Windsor Nature Discovery, LLC
www..nature-discovery.com
Why selective fisheries?
Harvest commingled populations at different rates.
1. Increase harvest rates on hatchery production.
2. Minimize impact to depressed and endangered stocks.
Visual mark—adipose fin clip
Short soaks and careful handling techniques
are not enough to improve long-term
survival of gill net captured chinook.
Combined with the tangle net, they do
improve long-term survival.
Chinook salmon with gill and wedge marks
Chinook salmon with tangle marks
Objectives
Compare 4.5” and 4.25” tangle nets.
Evaluate:
1, Immediate survival, catch efficiency, and bycatch.
2. Long-term (post-release) survival with jaw and PIT tags.
3. Controls released at two locations.
4. Passage timing.
Upriver
Toward Pacific Ocean
Fish Trap
Beacon Rock
Evaluate condition and length
Immediate survival
Study year
Mesh size (inches)
Immediate survival
%N
2003 Tangle 98.0 1172
No significant difference between immediate mortality for spring chinook salmon captured in 4.5” and 4.25” nets.
Catch efficiency for paired nets
2003: No significant difference between 4.5” and 4.25” tangle nets.
Bycatch
Primarily sturgeon and suckers
Reduced by avoiding fishing in concentration areas.
Preliminary 2003 survival estimates
GroupJaw tag recovery rate
PIT tag detection rate
Jaw tag survival estimat
e
PIT tag survival estimate
Control at Bonne. dam
19.0% 97.6% 65.4%(52.6-78.3)
79.8%(77.2-82.4)
Control below Bonne.
dam
16.5% 95.6% 75.2%(60.0-90.4)
81.5%(84.2-78.7)
Tangle net 12.7% 79.5%
Long-term survival measured by releasing fish to swim freely is very different than immediate survival or net pen holding survival.
PIT tag post-release survival estimates are similar to jaw tag post-release survival estimates.
Conclusions
Next steps:Evaluate passage timing.Evaluate survival excluding Bonneville detections.
Recommendations:Additional year with two controls. Additional year with PIT tags.Evaluate spawning success.