evaluating commercial selective fishing. c.e. ashbrook j.f. dixon a.hoffmann k. e. ryding e. a....

Evaluating commercial

selective fishing

C.E. AshbrookJ.F. DixonA. HoffmannK. E. RydingE. A. Schwartz J.R. SkalskiR. TownsendG.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 mark—adipose 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

Revival box

Jaw tag on adult chinook salmon

Chinook salmon with gill and wedge marks

Chinook salmon with tangle marks

Immediate survival

53696.8Tangle (3.5&4.5)2001

83699.0Gill (8)2001

190099.15.5” Net2002126299.5Tangle (4.5)2002117298.0Tangle (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.

Long term survival

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

Total survival based on Control at Bonneville Dam

100

88.3

52

67.356.8

68.2

0

20

40

60

80

100

120

control 2001 tangle 2001 8" gill 2002 tangle 2002 5.5" gill 2003 tangle

Percent survival

Gro

up

Total survival based on Control below Bonneville Dam

100 100

60.1

77.8

65.7

79.1

0

20

40

60

80

100

120

control 2001 tangle 2001 8" gill 2002 tangle 2002 5.5" gill 2003 tangle

Percent survival

Gro

up

2003—PIT 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%(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

Dam Tangle Control at Bonneville

Detection probability

Bonneville 855 1062 44.6%

McNary 417 497 45.6%

Three Mile 0 1 0%

Lower Granite 273 363 42.9%

Ice Harbor 290 371 43.9%

Priest Rapids 65 66 49.6%

Rock Island 32 38 45.7%

Wells 9 15 37.5%

Survival beginning at Bonneville Dam

Group N Detection probability

Ratio of probabilities

Unique treatment detections above Bonneville Dam

406 47.5% 1.04

Treatment detections at Bonneville Dam

855

Unique control detections above Bonneville Dam

486 45.8%

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

What’s 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 AssociationOregon 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.