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K:\018641-000\Admin\Docs\018641-000 MEMO September 2021 Fisheries survey Draft 178 E 9TH STREET | SUITE 200 | SAIN | 55101 | 651.286.8450 | WSBENG.COM
Memorandum
To: Jessica Vanderwerff Wilson
From: Jordan Wein, WSB
Date: September 16, 2022
Re: Arrowhead Fisheries Survey
Edina, MN
WSB Project No. 018641-000
BACKGROUND
Arrowhead Lake (MN DNR DOW #27004500) located in Edina, MN is a 22-acre lake with an
average depth of 4.5 feet with a maximum of approximately 8 feet. Hypoxia (lack of enough
oxygen to support living tissues) can occur in winter when ice and snow have prevented
reintroduction of dissolved oxygen to the lake. This can result in the observation of fish kills in
springtime when ice melts off the lake. In addition, in shallow lakes, hot and dry months in
summer can deplete oxygen to the point of summer fish kills. To prevent this, a common
management option is to install aeration systems to artificially add dissolved oxygen to the water
column. An aeration system with 3 diffusers near the southeast area of the lake were installed in
1994 to attempt to maintain a healthy fishery through conditions that usually result in hypoxia in
the lake (winterkill). However, a lack of knowledge of this fishery exists and thus the effect of the
aerators is not well known. This system is paid for by the lake association and maintenance is
coordinated by the service contractor through the City of Edina.
A standard MN DNR fishery was completed in 1995 and showed a species diversity of black
bullhead, green sunfish and fathead minnows using standard trap nets. This diversity seems to
suggest regular periods of hypoxia since these species are especially resistant to low levels of
dissolved oxygen. MN DNR permitted stocking of 400 bluegill sunfish and 600 largemouth bass
(both species susceptible to mortality in hypoxic conditions) occurred in 1994 by lake residents,
however no fish from that stock was recaptured indicating low or no survival of stocked species.
Since then, in 2016, the lake was stocked with 1000 bluegill fingerlings and 1000 yearlings as
well as 430 largemouth bass fingerlings and 90 yearlings. No MN DNR survey has been
conducted since then.
This memo describes the use of nets and electrofishing to conduct a standard fisheries survey at
Arrowhead Lake in Edina, MN. The results will give a baseline index for catch per unit effort
(CPUE) for comparison of subsequent surveys in order to understand population and diversity
dynamics as well as presence/absence of invasive species.
Fisheries Survey Report
September 16, 2022
Page 2
ARROWHEAD TRAP NET SURVEYS: SEPTEMBER 2021 AND JUNE 2022
Methods
We used three (3) MN DNR standard double frame fyke trap nets with ¾” mesh and a 60’ lead
line. In addition, we used three (3) mini fyke trap nets with 3/8” mesh and a 30’ lead line (seen in
Figure 1). This style of trap targets the natural movement patterns of fish along the shorelines
during a 24-hour period. Fish swimming along the shore are guided toward funneled throats that
allow the fish in but are not able to escape. The contents of each trap were emptied, all fish are
identified, and a representative sample was measured for length for comparative purposes.
Figure 1: Example of mini fyke trap net set in a lake.
Results
Both standard trap nets and mini fyke trap nets resulted in the same diversity of species: black
bullhead, bluegill sunfish, green sunfish, hybrid sunfish, and largemouth bass as shown in Figure
2. The most abundant species was bluegill sunfish with a CPUE of 18.17 in 2021 and 26 in 2022
and an average size of 5.8 inches and 6.7 inches respectively. Next most abundant was
largemouth bass with a CPUE of 2.17 in 2021 and 1.0 in 2022 and an average size of 13.1 inches
and 10.1 inches respectively. Black bullhead and green sunfish showed the same abundance
with CPUE of 0.17 in 2021 and an average size of 9.8 and 6.2 inches respectively. Green sunfish
were not captured in 2022 with trap nets.
Fisheries Survey Report
September 16, 2022
Page 3
Figure 2: Largemouth bass on left and bluegill on right from traps
Table 1: Fall total catch of each species using mini and standard trap nets compared to normal ranges.
September 2021 trap net sampling
Species Gear Total catch CPUE Normal range
Black bullhead Mini trap net 0 0.0 -
Black bullhead Standard trap net 1 0.2 1.8-26.3
Bluegill sunfish Mini trap net 88 14.7 -
Bluegill sunfish Standard trap net 109 18.2 2.8-43.3
Green sunfish Mini trap net 2 0.3
Green sunfish Standard trap net 1 0.2 .2-12.4
Hybrid sunfish Mini trap net 12 2.0 -
Hybrid sunfish Standard trap net 0 0.0 NA
Largemouth bass Mini trap net 6 1.0 -
Largemouth bass Standard trap net 13 2.2 .1-.8
Table 2: Breakdown of size classes of each species in fall of 2021.
2021 Length of select species sampled
Length
categories
Black
bullhead
Bluegill
sunfish
Green
sunfish
Hybrid
sunfish
Largemouth
bass
0-5 0 24 0 0 0
6-7 0 121 2 10 1
8-9 0 3 1 2 3
10-11 1 0 0 0 2
12-14 0 0 0 0 3
15-19 0 0 0 0 10
Fisheries Survey Report
September 16, 2022
Page 4
Table 3: Spring total catch of each species using mini and standard trap nets compared to normal ranges.
June 2022 trap net sampling
Species Gear Total catch CPUE Normal range
Black bullhead Mini trap net 1 0.2 -
Black bullhead Standard trap net 2 0.3 1.8-26.3
Bluegill sunfish Mini trap net 32 5.3 -
Bluegill sunfish Standard trap net 156 26.0 2.8-43.3
Green sunfish Mini trap net 0 0.0
Green sunfish Standard trap net 0 0.0 .2-12.4
Hybrid sunfish Mini trap net 0 0.0 -
Hybrid sunfish Standard trap net 0 0.0 NA
Largemouth bass Mini trap net 3 0.5 -
Largemouth bass Standard trap net 6 1.0 .1-.8
Table 4: Breakdown of size classes of each species in spring 2022.
2022 Length of select species sampled (trap nets and electrofishing)
Length
categories
Black
bullhead
Bluegill
sunfish Goldfish
Hybrid
sunfish
Largemouth
bass
0-5 0 9 0 0 2
6-7 0 160 0 3 1
8-9 0 13 0 0 8
10-11 9 0 0 0 0
12-14 1 0 5 0 6
15-19 0 0 0 0 3
As mentioned above, the MNDNR surveyed Arrowhead Lake in 1995 using similar trap net gear.
The comparison of CPUE for species sampled is displayed in Figure 3 below.
Fisheries Survey Report
September 16, 2022
Page 5
Figure 3: CPUE comparison of MN DNR survey in 1995 and WSB survey in 2021 using standard trap nets.
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
Black bullhead Bluegill Green sunfish Largemouth bassCPUE
Species
1995 survey 2021 survey
Fall 2021 Fisheries Survey Memo
December 6, 2021
Page 6
K:\018641-000\Admin\Docs\018641-000 MEMO September 2021 Fisheries survey Draft 178 E 9TH STREET | SUITE 200 | SAIN | 55101 | 651.286.8450 | WSBENG.COM ARROWHEAD BOAT ELECTROFISHING SURVEYS: AUGUST 2022
Methods
Boom electrofishing consists of a boat with an onboard gasoline generator that supplies power to
a dual boom cathode array that hangs off the front of the boat, as shown in Figure 4 below. A
control box run by the navigator adjusts the type of electrical output depending on lake depth,
temperature, and conductivity. Generally, the output runs around 18-22 amps and 2,000-3,000
watts. This amount of electricity caused a phenomenon known as electrotaxis, movement toward
an electric field, and as the fish entered the strongest area of electricity, they were immobilized
and were able to be netted without long term harm. The fish generally returned to normal
behavior between a few seconds to a few minutes after removal from the electric field. The zone
which immobilized fish was generally about four feet around each boom array and about four feet
deep.
Three transects around the lake of 15 minutes were completed. This allowed us to sample all
shoreline one time as well as a short portion down the middle of the lake. This prevented us from
double-counting fish that had already been captured in earlier transects.
Figure 4: Electrofishing survey on a lake
Results
A total of five species were sampled during the electrofishing survey: black bullhead, bluegill
sunfish, hybrid sunfish, largemouth bass, and goldfish. As seen with the trap nets, the most
abundant species was bluegill sunfish. A breakdown of species and average lengths is shown
below.
Fisheries Survey Report
September 16, 2022
Page 7
Table 5: Breakdown of species sampled during August 2022 electrofishing survey.
Total caught Average length (inches)
Black bullhead 7 10.1
Bluegill sunfish 58 7.8
Goldfish 5 13.5
Hybrid sunfish 3 7.2
Largemouth bass 11 9.5
Figure 5: One of the 5 goldfish captured during electrofishing surveys in Arrowhead.
Figure6: A naturalized/wild form of goldfish captured during electrofishing surveys.
CONCLUSIONS
Comparing the MNDNR survey in 1995 and our survey in 2021 (Figure 3) show a stark contrast
between the two different surveys. The 1995 survey captured species that are typical in lakes
that suffer frequent winter kills due to hypoxia. However, the turnover to species like bluegill and
largemouth bass suggests stocking of these species in 2016 was successful and there are
normally abundant in Arrowhead Lake.
Fisheries Survey Report
September 16, 2022
Page 8
Average individual size of the largemouth is somewhat small but a few individuals larger. It
appears aeration of the lake has successfully prevented winterkill of stocked bluegill sunfish and
largemouth bass since 2016 stocking events. This likely means that the average dissolved
oxygen does not extensively drop below 2 mg/liter at any time.
Finally, the somewhat surprising and potentially concerning finding was the presence of a small
number of large goldfish in the lake. Judging by the number of small number of them captured,
and the relative large size, it appears there is currently not an overabundant amount. All were of
sexually mature status, though, and could potentially recruit more goldfish if there were a drop in
bluegill abundance. Bluegill sunfish are likely the reason for the low goldfish abundance, as they
are effective predators of cyprinid fish like goldfish and carp.
If an effort to remove these large goldfish, an accurate population estimate and reduction in the
chances of goldfish recruitment could be effectively done with electrofishing surveys since the
lake is small.
Fisheries Survey Report
September 16, 2022
Page 9
APPENDIX:
Figure7:Map of aeration diffusers in Arrowhead Lake