Studying Goldfish in the Grace Chain of Lakes
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Project funded in part by the Clean Water Land & Legacy Act Amendment
Background
While doing routine monitoring in April 2019, Carver County Water Management Organization staff discovered thousands of goldfish in an inlet to Big Woods Lake in Chaska. It was the most densely populated discovery of goldfish staff had seen. The most likely reason for the goldfish presence is one or more individuals illegally dumping pet goldfish over the years. Big Woods Lake is part of the Grace Chain of Lakes, which also includes Lake Grace, Lake Jonathan, McKnight Lake, and Lake Hazeltine.
Goldfish impacts to the lakes
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Like many aquarium pets, goldfish are not native to Minnesota. When found in lakes and ponds, goldfish pose a threat to water quality and overall ecological health. Goldfish are hardy and very invasive like their close relative, the common carp. Both fishes stir up lake bottom sediments and uproot plants while feeding. This action releases phosphorus into the water, which increases algae and decreases water clarity. The uprooting of native plants removes habitat for the native fish that rely on them, and goldfish compete with native fish for food and shelter. Goldfish can reproduce rapidly, live to be 25 years old, are hardy and survive the low oxygen conditions in winter. Once established, no easy solution exists to remove an invasive species like goldfish.
Work plan and study
There has not been any comprehensive study about goldfish in a lake in the upper Midwest. And there is no scientific literature on the impacts of goldfish to a lake, how they affect water quality, or how they respond to removal events.
Spring of 2021, Carver County Water Management Organization received a grant from the Board of Water & Soil Resources for a three-year work plan to study and remove goldfish from Big Woods Lake and Lake Hazeltine where the largest populations of goldfish are found. The study will look at how, where, and when the goldfish move in the chain of lakes. The study will also look at what removal techniques work best and when.
Goals
- Get estimates for number of adult and juvenile present in the lakes.
- Study spawning and migration habits. Where they are spawning, where nurseries are, and how temperature affects their movements. Goldfish do not have annual consistent migration patterns.
- Identify nursery areas.
- Study how the goldfish population responds to removal efforts. Do populations rebound? Do goldfish avoid certain areas? Does effort to remove increase over time?
- Determine potential for long term management of this species.
This workplan is about learning. Many lakes in the metro area have goldfish infestations. The knowledge from this study can help other agencies understand the where goldfish likely spawn, how goldfish migrate through a lake system, how populations respond to fish removals, and the potential effort required to remove goldfish for a whole system.
How it works
In 2020, staff captured, tagged and released over 500 goldfish with passive integrated transponders, or PIT tags. These PIT tags are like the microchips used in pets and will be used to study movement data of goldfish.
Staff have installed 3 PIT antennas in areas around Big Woods Lake and Lake Hazeltine. Anytime a goldfish with a PIT tag swims past an antenna, the antenna reads it and staff know which fish it is and where. All fish captured will be checked for PIT tags to help us learn about movement of tagged fish and gain more info on percentage of the total population and groups in each location during springtime.
Removal events began in 2020. Staff have used techniques including box nets, seine nets, and dip nets. Staff are also studying the use of electroshocking as another method to stun the goldfish for easier collection for research purposes.
- In 2020, staff completed eight removal events and estimated over 100,000 goldfish were removed.
- In 2021, staff completed ten removal events and estimated over 1.6 million goldfish were removed.
- Thus far in spring 2022, staff have completed five removal events and removed about 3286 lbs. of goldfish.
Gathering the background data with fish surveys
After the fish were discovered in 2019, the first step was to study and better understand the population and diversity of fish in each of the chain of lakes. In summer of 2019, staff conducted fish surveys on all lakes but Hazeltine. Lake Hazeltine was not surveyed because it recently had a fish survey done by a consultant. Below is a summary. The full survey data can be viewed here.
Northern pike waiting to be released into Big Woods Lake
Stocking
After the survey, Carver County Water Management Organization stocked two dozen Northern Pike into Big Woods in late September 2019 to help control the goldfish population.
You can help
As we focus on removing goldfish, it is important that we don’t have new introductions. You can help by spreading the word about what do to if you have a pet you no longer want or can’t care for. The best thing to do is find it a new home. Donate it or take it to a surrender event. Surrender events are often hosted by the MN Aquarium Society. During surrender events, you can bring aquatic animals and plants and the hosting organization will help find them new homes. You can also check with local veterinarians and pet stores for surrender and new-home opportunities.
Can people fish, hunt or obtain the goldfish?
Minnesota state law prohibits transporting of live fish without the appropriate permit. A fishing license allows an individual to fish for them with hook and line, but you cannot transport them live. A fishing license is not a permit to transport live fish.
Bow hunting of fish is prohibited by City of Chaska ordinance. Currently, the city ordinance only allows for bow hunting of deer during the established Department of Natural Resource deer bow season and only in specific areas of Chaska, which does not include the Grace Chain of Lakes.
Goldfish cannot be used as bait. That is another way they get released into lakes and rivers.
The organization wants to discourage any movement of these fish. They are invasive and moving them increases the risk they could escape into another lake or river.