Determining our lake’s carrying capacity

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  • #146573 Reply
    James W Holden

    We live on a large freshwater lake (over 100 miles of shoreline) that is fairly shallow (average depth 20-feet), with warm water and an overabundance of algae and submerged aquatic vegetation which pose a nuisance, especially in the late summer. There are currently about 25 mute swans along about 8 miles of shoreline. They have so far posed no problems to other waterfowl (primarily ducks and Canada geese) and have caused no harm to humans, although they can be somewhat defensive during mating season and when defending their nests or cygnets. The question has arisen how to determine what the carrying capacity of the lake is before they might have an adverse effect on other waterfowl or vegetation and therefore need population control measures. How might we go about determining this?

    #146586 Reply
    Swan Expert

    Hi James

    We are frequently asked this question and have consulted for numerous sites for the past 30 years. An 80-acre lake can hold 100 swans with little impact, so if your lake is as large as you indicate, 25 swans pose no harm. Additionally, the swans will help trim back certain types of sub aquatic vegetation (SAV) and will eat certain types of algae. Furthermore, current studies show:

    Mute Swans are no more aggressive than any other wildlife protecting their family and habitat.

    Mute Swans are not detrimental to other waterfowl as the swans are more aggressive towards their own species.

    Mute Swans feed on sub-aquatic vegetation because their long necks allow them to feed below the water’s surface. The swans trim back the SAV, but do not deplete the SAV. In doing so, they increase the biodiversity of the habitat by attracting other species. For instance, dabbling ducks feed on SAV brought to the surface by the Mute Swans. This SAV is a source of food for the dabbling ducks that could not otherwise reach below the water’s surface to feed.

    Mute Swans are a Sentinel species alerting scientists to the presence of heavy metals and harmful microrganisms in the habitat. In fact, in Sweden there are 10,000 Mute Swans in an area smaller than what you are describing. If one swan dies, Swedish law mandates an immediate investigation to insure that a larger problem within the environment is not occurring.

    So, you have a healthy population of Mute Swans and if properly monitored, the Mute Swans can help provide information on the health of your lake’s environment. We hope this information is of benefit. The Regal Swan

    #147025 Reply
    James W Holden

    Thanks for the information. Very much appreciated. Because of public outcry and resistance from the Lake County Board of Supervisors the California Department of Fish and Wildlife has withdrawn their extermination plan “for the time being”. We are forming a “Save Our Swans Clear Lake Society” to oppose future such proposals and to offer a rational proposal for setting the lake’s carrying capacity and managing the population once it reaches that capacity, which is likely to a decade or more down the road. We are looking at addling of eggs as the most reasonable and humane method of population control.

    #148580 Reply
    James W Holden

    I shared your response with the California Department of Fish and Wildlife biologist who proposed the eradication of our mute swans. He replied that “The information is interesting but lacks citations commonly seen in scientific literature. I have been reviewing quite a bit of cited and published literature that dies [sic] not support the opinions you are sending. I am open to a discussion or to reading cited literature backing your emails.” Can you provide me with citations of appropriate literature?

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