Using PIT tags to evaluate the postrelease survival of spring chinook
salmon following their release from
commercial nets
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Discovery, LLC
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C. E. Ashbrook, J. R. Skalski, K.W.Yi, R. Townsend, J.F. Dixon, and E. Schwartz
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.
Toward Pacific
Ocean
Beacon Rock
Fish Trap
Upriver
Evaluate condition and length
Immediate survival
Study
year
Mesh size
(inches)
Immediate
survival %
2003
Tangle
98.0
N
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
Jaw tag
recovery
rate
PIT tag
detection
rate
Jaw tag
survival
estimate
PIT tag
survival
estimate
Control at
Bonne. dam
19.0%
97.6%
65.4%
79.8%
(52.6-78.3)
(77.2-82.4)
Control below
Bonne. dam
16.5%
75.2%
81.5%
(60.0-90.4)
(84.2-78.7)
Tangle net
12.7%
Group
95.6%
79.5%
Conclusions
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.
Next steps:
Evaluate passage timing.
Evaluate survival excluding
Bonneville detections.
Recommendations:
Additional year with two controls.
Additional year with PIT tags.
Evaluate spawning success.