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:
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.
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
Immediate survival 53696.8Tangle (3.5&4.5) 2001 83699.0Gill (8) 2001 190099.15.5 Net2002 126299.5Tangle (4.5) 2002 117298.0Tangle (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.
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
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 DamTangleControl at Bonneville Detection probability Bonneville855106244.6% McNary41749745.6% Three Mile010% Lower Granite27336342.9% Ice Harbor29037143.9% Priest Rapids656649.6% Rock Island323845.7% Wells91537.5%
Survival beginning at Bonneville Dam GroupNDetection probability Ratio of probabilities Unique treatment detections above Bonneville Dam 40647.5% 1.04 Treatment detections at Bonneville Dam 855 Unique control detections above Bonneville Dam 48645.8% 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
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.