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HomeMy WebLinkAboutAL Interim Fisheries Report_January 2022 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: January 14, 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 7 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 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. This event was conducted between September 19, 2021 through September 21, 2021. Fall 2021 Fisheries Survey Memo January 14, 2022 Page 2 ARROWHEAD TRAP NET SURVEYS: SEPTEMBER 2021 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. Fish swimming along the shore is guided toward funneled throats the allow the fish in but is not able to escape. The contents of each trap are emptied, all fish are identified, and a representative sample is 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. Fall 2021 Fisheries Survey Memo January 14, 2022 Page 3 Figure 2: Largemouth bass on left and bluegill on right from traps Figure 3: Catch per unit effort (CPUE) by species and trap type in 2021. 0 20 40 60 80 100 120 Black bullhead Bluegill Green sunfish Hybrid sunfish Largemouth bassNumber of fish caughtSpecies Mini TrapNet Standard TrapNet Fall 2021 Fisheries Survey Memo January 14, 2022 Page 4 Figure 4: Average length by species and trap type in 2021. 0 2 4 6 8 10 12 14 16 18 Black bullhead Bluegill Green sunfish Hybrid sunfish Largemouth bassAverage length (inches)Species Mini TrapNet Standard TrapNet Fall 2021 Fisheries Survey Memo January 14, 2022 Page 5 Figure 5: CPUE comparison of MN DNR survey in 1995 and WSB survey in 2021 using standard trap nets. For comparison purposes, the following will focus the CPUE only from standard trap nets since both the 1995 and 2021 surveys used standard sizes. The most abundant species was bluegill sunfish with a CPUE of 18.17 and an average size of 5.8 inches. Next most abundant was largemouth bass with a CPUE of 2.17 and an average size of 13.1 inches. Black bullhead and green sunfish showed the same abundance with CPUE of 0.17 and an average size of 9.8 and 6.2 inches respectively. 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 CONCLUSIONS Preliminary results 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. Follow up surveys in spring of 2022 will continue to establish the status of the fishery after an additional winter has passed. Fall 2021 Fisheries Survey Memo January 14, 2022 Page 7 APPENDIX: Figure 4:Map of aeration diffusers in Arrowhead Lake