Presentation on theme: "Evaluating commercial selective fishing. C.E. Ashbrook J.F. Dixon A.Hoffmann K. E. Ryding E. A. Schwartz J.R. Skalski R. Townsend G.E. Vander Haegen K.W."— Presentation transcript:
Evaluating commercial selective fishing
C.E. Ashbrook J.F. Dixon A.Hoffmann K. E. Ryding E. A. Schwartz J.R. Skalski R. Townsend G.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 markadipose 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
Jaw tag on adult chinook salmon
Chinook salmon with gill and wedge marks
Chinook salmon with tangle marks
Immediate survival Tangle (3.5&4.5) Gill (8) Net Tangle (4.5) Tangle (4.25&4.5) 2003 N Immediate survival % Net Type (inches) Study year
Catch efficiency for paired nets 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 inch gill net captured 1.5 times more fish than 4.5 inch tangle net 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
new control tangle control gill tangle control gill tangle control 95% confidence interval Estimated total survival (%) Jaw tag recovery rate (%) Group
2003PIT 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% ( ) 79.8% ( ) PIT tag survival estimate 79.1% ( ) 68.2% ( ) Jaw tag survival estimate Group 79.5% 95.6% 97.6% PIT tag detection probability
PIT tag data by dam DamTangleControl at Bonneville Detection probability Bonneville % McNary % Three Mile010% Lower Granite % Ice Harbor % Priest Rapids % Rock Island % Wells %
Survival beginning at Bonneville Dam GroupNDetection probability Ratio of probabilities Unique treatment detections above Bonneville Dam % 1.04 Treatment detections at Bonneville Dam 855 Unique control detections above Bonneville Dam % 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
Whats 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 Association Oregon 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.