Poplar River Fisheries Summary and Trends 10 September 2008

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Poplar River Fisheries – Summary and Trends
10 September 2008
The Poplar River is a designated trout stream, flowing 21.7 miles from its source at Gust Lake to Lake Superior. From its mouth to about 17 river miles above Lake Superior it supports a wild brook trout population, with the highest population densities occurring in the upper end of that reach. A falls blocks movement of fish from Lake Superior about 400 feet above the mouth of the river, but the short stretch below the falls supports a spring run of rainbow trout (steelhead), fall runs of pink, chinook, and coho salmon, and a fall run of lake-run (coaster) brook trout. Riparian lands along the lower 2.6 miles of the river are privately owned, limiting public access to that reach. Because of the lack of public access, the lower Poplar River has not been stocked by the Minnesota Department of Natural Resources (MNDNR). Some private stocking of trout in the lower reach was done several years ago.
Water quality concerns have been centered around the lower 2.6 miles of the stream, and the rest of this summary will concentrate on what is known about fisheries in that section of the river. The MNDNR has done little fish population sampling in the lower reach, and no sampling was done prior to 1983. No sampling was done in section of the reach above the barrier falls prior to 1990. Lack of earlier sampling means that all the information available to the MNDNR is post-development; the lower reach was already disturbed or impaired to some degree when the MNDNR started sampling.
The brook trout population in this reach is small by comparison to population levels farther upstream, and by comparison to other streams in this area (Table 1). The population at present appears to be supported by recruitment from upstream areas; catches of young-of-year (YOY) brook trout have been very low. Adult brook trout collected by the MNDNR above the barrier falls have ranged in length from 5.5 to 12 inches, with most lying between 5.5 and 8.5 inches. This size distribution is typical for an inland stream population in this area. In the late fall the stream supports a small run of coaster brook trout (fish that live most of the year in Lake Superior). Some larger brook trout have been taken in MNDNR (Lake Superior office) sampling of the fall coaster run. Sampling conditions were difficult in 2007 due to high flows, but brook trout as large as 16.6 inches were taken below the barrier falls. Coaster brook trout cannot pass the barrier falls. Recruitment sources for the coaster population are unknown. YOY brook trout have rarely been found below the barrier falls, suggesting that at present this population may be supported by recruitment from the upstream population, or by reproduction occurring in other streams in the area.
MNDNR has no information on fishing pressure targeting brook trout in the lower reach of the river, above the barrier falls. Due to limited public access, it has been assumed to have been light.
The stream supports an active steelhead fishery in the section below the barrier falls. Creel surveys covering the spring steelhead season done by the MNDNR Lake Superior office since 1992 have yielded fishing pressure estimates ranging from 168 to 1,347 angler-hours, with estimated steelhead catches (unclipped, or wild, fish over 16 inches only) ranging from zero to 194 fish (Table 2). Since 2004 fishing pressure estimates have ranged from 173 to 548 angler-hours, and estimated steelhead catches have ranged from 32 to 133 fish. Fishing pressure during the spring steelhead season has been lower in recent years (2004-2007) than pressures observed in the early 1980s and the early 1990, but catch rates for steelhead have been higher.
The stream also supports an active fall fishery for chinook and pink salmon; a chinook salmon from the Poplar River shares the current state record for the species. Recent creel survey data for the fall fishery are lacking; fall creel surveys were done in 1989, 1991, and 1992. Fishing pressure estimates ranged from 182 (1992) to 1,337 angler-hours (1989). No fish were observed by the clerk in 1991 or 1992; in 1989 an estimated 167 pink salmon were caught.
Summer MNDNR fish sampling in the area below the barrier falls has yielded low catches of juvenile steelhead and brook trout. Catches for both species have been well below normal ranges for the area in every assessment, indicating limited reproductive success (Table 3). Given the variability inherent in CPUE data, no trends in juvenile abundance in this reach since 1983 can be identified.
There is some evidence to suggest that some warmwater species have been increasing in number in the lower Poplar River. Catches of smallmouth bass in the reach below the barrier, while fluctuating from year to year, have been unusually high in several assessments done since 1994 (Table 3). Pumpkinseed sunfish and bluegill have also been observed in that reach since 1994 (Table 4).
Information available to MNDNR Fisheries on changes in water quality in the Poplar River is largely anecdotal. In 1994 and 1995, MNDNR Fisheries crews reported clay and silt sediment knee-deep in places in the pools just above the mouth. Prior to that time the pool areas were relatively clean. In a 1961 survey, that area (Sector I, mouth to the first falls) had a bottom consisting of 67% rubble, 10% boulder, 10% gravel, 10% sand, and 3% silt. Rainbow trout and brown trout were present, and based on visual observation, were described as abundant. In a 1989 DNR Fisheries stream survey, bottom types in the same stretch were reported to have been boulder, rubble, and gravel, with no silt or muck reported.
Primary limiting factors for brook trout and steelhead in the lower 2.6 miles of the river are probably lack of spawning habitat (for both species), and marginal water temperatures (for brook trout). Low winter flows may also be a limiting factor in some years, resulting in heavy anchor ice formation that can scour riffles, destroy redds, and leave over-wintering fish dependent on sub-surface flows recharging the remaining deeper pools. Lack of spawning habitat is evidenced by low production of YOY fish. For steelhead and coaster brook trout, limited areas with suitable substrate (coarse gravels), siltation of those areas, and the short length of stream available for spawning are critical. Resident (non-coaster) brook trout have much more river available, but the reach is dominated by coarse substrates, and subjected to siltation. Summer water temperatures can be high, and while not lethal, may stress resident brook trout.
Trout populations in the lower reach would benefit by actions designed to reduce siltation, promote a narrower, well-shaded channel, and preserve adequate flows. Reduction of siltation could be accomplished by changes in watershed management and by stabilization of eroding slopes and banks within the lower watershed. A narrower, well-shaded channel could be accomplished by reducing spate flows caused by high snow-melt runoff and poor water retention, by selected channel restoration, and by planting of long-lived conifers in areas where overhead cover is lacking. Adequate flows could be preserved by improving retention of water on the landscape, and by limiting withdrawals during critical low-flow periods (which have yet to be defined).

Information for this summary was provided by MNDNR Fisheries staff in Duluth (Lake Superior Fisheries) and Grand Marais.

Steve Persons

Area Fisheries Supervisor

DNR Fisheries

1356 E. Hwy 61

Grand Marais, MN 55604
(218) 387-3056


Table 1. Electrofishing catch per unit effort (CPUE; fish/minute) for young-of-year (YOY) and age-1 or older (1+) brook trout (BKT) and rainbow trout (RBT) in sampling stations located near the mouth (mile 0.0), below the ski hill (mile 1.0), and within the upper reach (mile 16.2) on the Poplar River, Cook County, Minnesota.

Mile 0.0 Mile 1.0 Mile 16.2

Year YOY 1+ YOY 1+ YOY 1+ YOY 1+

1983 0.18 0.00 0.00 0.12

1989 0.02 0.04 0.00 0.02 0.59 0.66

1990 0.02 0.13 0.54 1.15

1991 0.00 0.10 1.16 1.70

1992 0.00 0.00 0.68 0.58

1994 0.00 0.00 0.00 0.12

1995 0.00 0.00 0.00 0.11

1998 0.00 0.09 0.00 0.03 3.40 2.80
2002 0.00 0.00 0.00 0.00
2006 0.00 0.00 0.00 0.00 0.00 0.04 0.18 0.66

2007 0.16 0.08 0.03 0.03 0.00 0.03 0.27 0.12

Normal CPUE ranges (as indicated by first and third quartile values for the area) for brook trout YOY and 1+ are 0.12-0.92 and 0.14-1.00 fish/minute, respectively. Normal CPUE ranges for rainbow trout YOY and 1+ are 0.99-6.90 and 0.24-1.54 fish/minute, respectively.

Table 2. Annual estimates of fishing pressure (angler-h), rainbow trout catch (number of unclipped fish longer than 16 in), and rainbow trout catch per unit effort (fish/angler-h) in the lower reach of the Poplar River, Cook County, Minnesota, during the spring steelhead season.

Year Fishing Pressure Catch Catch Rate

1981 1,394 ND

1982 716 ND

1983 1,170 61 0.052

1992 555 65 0.118

1993 1,347 31 0.023

1994 1,083 139 0.129

1995 732 0 0.0

1996 496 194 0.391

1997 361 12 0.034

1998 478 0 0.0

1999 469 48 0.102

2000 549 122 0.223

2001 168 0 0.0

2002 270 0 0.0

2003 278 12 0.041

2004 424 133 0.314

2005 173 32 0.186

2006 338 87 0.257

2007 548 63 0.116

Table 3 Electrofishing catch per unit effort (CPUE; fish/minute)at various sampling dates (month/year), for young-of-year (YOY) and age-1 or older (1+) brook trout (BKT), rainbow trout (RBT), and smallmouth bass (SMB), and CPUE for longnose dace (LND), sculpins (SCU; mottled or slimy), white sucker (WTS), and burbot (BUB) of all ages in the Poplar River, Cook County, Minnesota, from the mouth to the first falls.



8/83 0.00 0.12 0.00 0.18 0.00 0.00 1.50 0.00 0.06 0.42

9/89 0.00 0.02 0.02 0.04 0.06 0.04 0.57 0.02 0.04 0.31
9/94 0.00 0.12 0.00 0.00 0.00 0.02 0.28 0.02 0.19 0.21
9/95 0.00 0.11 0.00 0.00 0.30 0.03 0.00 0.00 0.11 0.08
8/98 0.00 0.03 0.00 0.09 0.00 0.16 0.28 0.00 0.00 0.31
8/02 0.00 0.00 0.00 0.00 0.00 0.41 0.20 0.00 0.00 0.03
8/06 0.00 0.00 0.00 0.00 0.00 0.00 0.10 0.00 0.07 0.24
8/07 0.03 0.03 0.16 0.08 0.00 0.36 0.78 0.00 0.03 0.16

Normal CPUE ranges (as indicated by first and third quartile values for the area) for smallmouth bass YOY and 1+ are 0.02-0.06 and 0.03-0.12 fish/minute, respectively, among assessments where the species and age group has been collected. Smallmouth bass have been taken in less than seven percent of stream assessments done in this area.

Table 4. Fish species collected in MNDNR summer fish population assessments in sampling stations below the barrier falls (Mile 0.0) and above the barrier falls (Mile 0.1-2.6), on the Poplar River, Cook County, Minnesota, 1983 - 2007.

Species Mile 0.0 Mile 0.1-2.6

Blacknose Dace X

Bluegill X X

Brook trout X X

Burbot X*

Central mudminnow X

Common shiner X X

Creek chub X

Fathead minnow X*

Hybrid sunfish X*

Longnose dace X X

Longnose sucker X*

Mottled sculpin X

Northern pike X

Pink salmon X*

Pumpkinseed sunfish X*

Rainbow trout X X

Sea Lamprey X*

Smallmouth bass X X

Slimy sculpin X X

White sucker X

Yellow perch X X

* - found only at this location in the Poplar River.

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