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.