 In 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 |
