HomeMy WebLinkAbout2022 Indianhead Fisheries and DO profiles survey REPORT
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
Memorandum
To: Jessica Vanderwerff Wilson
From: Jordan Wein, WSB
Date: August 28, 2022
Re: Indianhead Fishery Survey and Dissolved Oxygen Profiles
Edina, MN
WSB Project No. 018642-000
BACKGROUND
Indianhead Lake (MN DNR DOW #27004400) located in Edina, MN, is a 14-acre lake with an
average depth of 4.5 feet with a maximum of 6 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 consisting of
4 aerators spread throughout the lake was installed in 1979 as part of a Clean-Flo system to
control algae and submerged plants. Furthermore, the aeration system served to prevent
conditions that usually result in hypoxia in the lake and fish winterkill. However, a lack of
knowledge of this fishery existed and thus the effect of the aerators was not well known. This
system was paid for by the lake association and maintenance is coordinated by the service
contractor through the City of Edina.
To this point, there had not been a standard MN DNR fishery assessment using standard trap
nets or electrofishing. Therefore, it is believed this is the first standardized survey efforts on the
lake. In the last 10 years, MN DNR permitted stocking has occurred in 2013 and 2016, stocking
native species like bluegill sunfish (200 and 5000 respectively) black crappie, (50 and 2000
respectively) and largemouth bass (200 and 1900 respectively). This stocking was paid for by
lake residents. The desire was to promote a healthy, native fisheries balanced for sustainable fish
populations.
The results of these surveys 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.
INDIANHEAD 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 traps targets the natural movement patterns of fish along the shorelines
during a 24-hour period. Once the lead line is anchored to shore, the trap is stretched
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 2
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
perpendicular to the shoreline and held up with an anchor. 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 were identified, and a representative sample were 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
crappie, bluegill sunfish, golden shiner, hybrid sunfish, and largemouth bass as shown in Figure
2. The most abundant by far were bluegill sunfish with an average size of 6.7 inches, followed by
hybrid sunfish at an average length of 8.2 inches, then black crappie at 7.3 inches, golden shiners
at 6.9 inches and finally largemouth bass at 10.6 inches (see Figures 3 and 4 below).
Figure 2: On the left, snapping turtles were regularly caught in out traps as well as bluegills, black crappie
and golden shiners shown on the right.
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 3
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
Table 1: Fall total catch of each species using mini and standard trap nets compared to normal ranges.
September 2021 sampling
Species Gear Total catch CPUE Normal CPUE range
Bluegill sunfish Mini trap net 470 78.3 -
Bluegill sunfish Standard trap net 530 88.3 2.8-43.3
Black crappie Mini trap net 18 3.0 -
Black crappie Standard trap net 83 13.8 1.2-20.5
Golden shiner Mini trap net 2 0.3 -
Golden shiner Standard trap net 13 2.2 .4-3.9
Hybrid sunfish Mini trap net 50 8.3 -
Hybrid sunfish Standard trap net 42 7.0 NA
Largemouth bass Mini trap net 3 0.5 -
Largemouth bass Standard trap net 3 0.5 .1-.8
Table 2: Breakdown of size classes of each species in fall of 2021.
2021 Length of select species sampled
Length categories
(inches)
Bluegill
sunfish
Black
crappie
Golden
shiner
Largemouth
bass
0-5 14 3 0 0
6-7 112 45 8 0
8-9 94 27 7 1
10-11 0 9 0 2
12-14 0 0 0 3
15-19 0 0 0 0
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 4
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
Table 3: Spring total catch of each species using mini and standard trap nets compared to normal ranges.
June 2022 sampling
Species Gear Total catch CPUE Normal CPUE range
Bluegill sunfish Mini trap net 843 140.5 -
Bluegill sunfish Standard trap net 456 76.0 2.8-43.3
Black crappie Mini trap net 8 1.3 -
Black crappie Standard trap net 23 3.8 1.2-20.5
Golden shiner Mini trap net 0 0.0 -
Golden shiner Standard trap net 7 1.2 .4-3.9
Largemouth bass Mini trap net 8 1.3 -
Largemouth bass Standard trap net 1 0.2 .1-.8
Table 4: : Breakdown of size classes of each species in spring 2022.
2022 Length of select species sampled
Length categories
(inches)
Bluegill
sunfish
Black
crappie
Golden
shiner
Largemouth
bass
0-5 14 0 0 0
6-7 180 12 4 3
8-9 80 17 3 2
10-11 8 4 0 3
12-14 0 2 0 5
15-19 0 0 0 3
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 5
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
INDIANHEAD 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 3 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, it was immobilized and
was able to be netted without long term harm to the fish. 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 3: Electrofishing survey on a lake
Results
A total of four species were sampled during the electrofishing survey. As seen with the trap nets,
the most abundant species was bluegill sunfish. Relatively fewer black crappie were sampled
compared to largemouth bass and golden shiners were not sampled. A breakdown of species
and average lengths is shown below.
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 6
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
Table 5: Breakdown of species sampled during August 2022 electrofishing survey.
Total caught Average length (inches)
Black crappie 4 8.2
Bluegill sunfish 119 6.2
Bluegill young of year 70 1.2
Hybrid sunfish 2 7.4
Largemouth bass 7 10.6
DISSOLVED OXYGEN ASSESSMENT: MONTHLY SURVEYS FROM AUGUST
2021 THROUGH JULY 2022
Methods
Dissolved oxygen (DO)
profiles were surveyed in
Indianhead Lake once per
month from August 2021
through May 2022. In June
and July of 2022, profiles
were collected twice per
month approximately 2
weeks apart. December and
January profiles were not
collected due to unsafe ice
conditions.
Using a YSI dissolved
oxygen meter and
thermometer, DO and
temperature were collected
at one-foot intervals until the
lake bottom was contacted.
DO was not collected on the
bottom of the lake or at the
water’s surface due to
confounding results because
turbulence could significantly
change the immediate
reading of the device. Six
locations were chosen based
on proximity to aerator
heads. The intention was to have two locations consistently surveyed near to aerators and four
locations nearer to shore away from the aerators to detect the lateral mixing difference throughout
the lake.
Figure 4: YSI equipment sensing DO at a depth during a winter survey on
Indianhead Lake.
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 7
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
Figure 5: Locations of repeated DO sampling each month.
Results
Although DO readings were collected at each 1-foot interval, there generally was little difference
between depths. At times, the readings at a depth of 1 foot from the surface were higher than the
rest, but much of that difference was attributed to acute surface disturbance like slight splashing
of waves on the canoe. We chose to display the average DO at a depth of 4 feet since all
locations were at least this deep before contacting the bottom sediments and it would be farthest
from surface disturbance to skew results. In addition, this would be the closest average depth
most fish in this lake type would be occupying. Therefore we felt it most pertinent to display any
problem areas for DO to cause distress to fish in the lake.
In general, it appeared there was a consistent average DO at this depth around 5.5 mg/l.
Sensitive species like bluegill sunfish become significantly distressed when DO falls below 2 mg/l.
These results show that DO in the water column appear to be maintained throughout the year
well above that threshold and assuming normal operation of the aeration systems, fish species in
Indianhead are at little risk of significant stress due to low DO.
Figure 5 is displayed comparing proximity to aeration heads (far and near) to determine lateral
mixing of DO. Although it appears to show a drop in DO at locations far from aeration heads, the
difference is minimal. For perspective, the far locations were between 250-400 feet away from
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 8
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
the heads, which is still relatively quite close to them. Regardless, the aerators appear to be
spreading DO evenly across the lake.
The DO appears to increase in the fall and into the winter as waters cool and the water is able to
hold more DO. The drop back to the level of about 5.5 mg/l in February may have been due to
fish respiration and ice cover reducing the introduction of DO from the surface. With the lack of
submergent vegetation to photosynthesize under the ice, there was a lack of oxygen being
released by plants. However, the lake still appeared to maintain DO above a significantly
stressful level for sensitive fish species. As ice melted off in March, the DO is seen to jump
significantly until water temperatures rose in May when the oxygen holding capabilities of the lake
also dropped.
Figure 6: Average DO measurements from August 2021 through July 2022 at a depth of 4 feet.
CONCLUSIONS
Results support the assumption that the stocking efforts in 2013 and 2016 were successful and
recruitment (survival of fish spawned within the lake) could be occurring. However, the lack of
abundant small fish (<3 inches) during trap net surveys suggested low recruitment, but high
survival of stocked fish. Electrofishing surveys did result in the sampling of a small number of
young of year sunfish, likely bluegills. This is likely the main forage for the largemouth bass found
in the lake. Regardless, the fishery seems to have benefitted from stocking efforts and the
installation of aeration systems.
0
2
4
6
8
10
12
14
Aug Sep Oct Nov Feb Mar Apr May Jun Jul
2021 2022Axis TitleAverage dissolved oxygen readings at a depth of 4 feet
Far
Near
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 9
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
Body conditions of some black crappie captured suggested low forage or disease could be
limiting their growth and recruitment. If small forage like fathead minnows or small golden shiners
were more prevalent, there may be enough to support better growth and health of crappies in the
lake. The lack of submergent aquatic vegetation could also be contributing to the lack of
recruitment of species other than bluegill and largemouth bass.
Indianhead Fisheries and DO profiles survey
August 28, 2022
Page 10
K:\018642-000\Admin\Docs\018642-000 Indianhead Fisheries and DO profiles survey REPORT
APPENDIX
Figure 7: Map of aerator diffusers in Indianhead Lake