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Fish FISH DIVISION
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Northern Pikeminnow Management

taggingIn 1990 regional managers approved the use of targeted fisheries for harvesting northern pikeminnow (formerly known as northern squawfish) within the lower Columbia and Snake rivers. Earlier research (1983 – 1986) had indicated that predation related juvenile salmonid mortality was substantial, larger northern pikeminnow were more piscivorous and more susceptible to angling, and that a modest removal (10 – 20% exploitation per year) of northern pikeminnow could result in a disproportionately large reduction in predation. Three fisheries have since been used in an attempt to employ this strategy. Site specific gill nets (1994 – 2002) were focused near areas where high levels of predation might occur (e.g. hatchery release points and dams). Angling by trained personnel directly from dams (1991 – 2002, 2006), was intended to target larger, highly predacious northern pikeminnow. The site specific gill net fishery and dam-angling met with only limited success; the bulk of the approximately 2.6 million northern pikeminnow removed under the auspices of the Northern Pikeminnow Management Program (NPMP) have been harvested by anglers participating in a sport-reward fishery.

Details...

The Oregon Department of Fish and Wildlife (ODFW) has two primary responsibilities in the NPMP. The first is to monitor the exploitation of northern pikeminnow by program anglers, and use this information to estimate potential reductions in predation. This is done by marking northern pikeminnow with an easily identifiable tag and monitoring the number, size and location of program caught recaptured fish. Our modeling results – based on exploitation rates – indicate that potential predation on juvenile salmonids by northern pikeminnow has decreased. Considering that approximately 16 million of the overall 200 million migrating juvenile salmonids in the Columbia River were once consumed by northern pikeminnow annually, the reductions we’ve modeled likely translate into at least 4 million additional juvenile salmonids escaping northern pikeminnow consumption on a yearly basis. 

The second of ODFW’s primary responsibilities is to monitor the predator fish community, including smallmouth bass, walleye, and the surviving northern pikeminnow for signs of response to the fishery (e.g. increases in population density, predation on smolts, reproduction, or growth by any of the remaining predators). Decreases in juvenile salmonid mortality from a specific source, in our case northern pikeminnow predation, can be subject to compensation from other sources; however, other than localized increases in smallmouth bass abundance – which may not be attributable to the removal of northern pikeminnow – no compensatory responses from the remaining fish predators have been detected. However, such a response in the future is still very possible, and c ontinued monitoring of the NPMP is prudent. We will continue to observe catch and exploitation rates of northern pikeminnow annually, and plan to examine northern pikeminnow, smallmouth bass, and walleye population dynamics and diet for signs of compensation every 3-5 years.

Annual harvest and exploitation rates for northern pikeminnow fisheries, 1990-2005. The minimum size for qualifying pikeminnow decreased from 11 to 9 inches in 2000. Dam angling and gill net fisheries were discontinued after 2002.

Year

Sport Reward

Dam Angling

Gill Net

Exploitation Rate

1990

4,681

11,001

--

--

1991

153,508

39,196

--

--

1992

186,904

27,868

--

--

1993

104,616

17,210

1,772

8.1%

1994

129,434

16,097

9,024

13.1%

1995

199,600

5,299

9,484

15.6%

1996

156,538

5,455

6,165

12.9%

1997

119,047

3,517

2,806

9.5%

1998

108,372

3,480

3,035

11.5%

1999

114,687

3,559

1,604

12.6%

2000

189,461

423

557

11.0%

2001

240,894

2,751

523

15.5%

2002

201,396

7

712

10.6%

2003

196,555

--

--

10.5%

2004

267,414

--

--

17.0%

2005

240,955

--

--

16.3%

The NPMP is funded by the Bonneville Power Administration. The Predator Studies project leader is Erick Van Dyke.

Reports and Publications by CRI Staff

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