Guest View: Tahoe Keys research seeks to control aquatic invaders
This summer, researchers will begin a project aimed at halting the spread of invasive species in Lake Tahoe. While the Tahoe Keys are the focus, the work is important for all of us who live around the lake, take advantage of its recreational opportunities, appreciate its beauty or depend on tourism for our livelihood.
Most of us are familiar with the efforts to keep destructive quagga mussels out of the lake. While we’re winning that battle for now, other invaders – such as the aquatic plants Eurasian watermilfoil and curlyleaf pondweed and the warmwater fish largemouth bass and bluegill – are already established.
In the late 1800s, Lahontan cutthroat trout, Tahoe sucker, Lahontan redside shiner, mountain whitefish, Paiute sculpin and Lahontan tui-chub were the native inhabitants of the lake. Introduction of non-native fish first occurred 130 years ago, and in the early 1980s, warm-water fish were found in the Tahoe Keys. These fish were not part of any state stocking effort.
In the 1960s and early ’70s, the Keys were constructed in a historic wetland populated by native aquatic plants such as coontail, sago pondweed and Richardson’s pondweed. The first mention of “milfoil” at Taylor Creek occurred in 1975, but non-native Eurasian watermilfoil was confirmed in 1995 and it has continued to spread. By 2009, surveys showed that Eurasian watermilfoil and coontail are the most abundant aquatic plants. Non-native curlyleaf pondweed has spread up to Lakeside Marina.
Eurasian watermilfoil and curlyleaf pondweed form dense mats that impede swimming and boating and are costly to remove. These invasive plants and warm-water fish compete successfully against native species, disrupting the ecological balance of the lake.
Recognizing the threat posed by invasives, more than 20 public and private organizations work to protect the lake through education, research, prevention, early detection, rapid response and control under the umbrella of the Lake Tahoe Aquatic Invasive Species Working Group.
The group obtained Southern Nevada Public Land Management Act funds to investigate the relationship between invasive weeds and warm-water fish. Are invasive plants providing warm-water fish the habitat they need to survive? What’s the best way to remove the weeds?
Aquatic weed removal in the Tahoe Keys relies on barge-mounted cutters and harvesting operations during peak growth. While this creates open channels for boats, it also generates fragments that disperse and can grow elsewhere, may stimulate invasive plant growth by opening up more areas to sunlight and can result in incidental bycatch of native fish and invertebrates.
The project will test three methods for physically removing Eurasian milfoil and curlyleaf pondweed – bottom barriers, physical removal by divers and mechanical cutting and harvesting – against control sites. At the same time, scientists will study fish presence and movement in both treated and non-treated areas.
The location will be 12 canals in the Tahoe Keys and the sailing lagoon (one of the control sites). The only impact to the community will be brief closures to boating of canals where divers are working. No fish removal will occur – only catch and tagging.
Researchers would eventually like to use a water-soluble fluorescent dye to understand how herbicides would move through the Keys and some infested offshore sites if they were used for weed control. The dye is not harmful and is not visible to the casual observer. Scientists would use fluorometers to detect its movement. The results will help determine the best placement and application methods for herbicides and indicate retention time and movement of a simulated herbicide application.
Ultimately, the community must make decisions about our vision for the lake. How aggressive do we want to be in controlling invasive weeds and fish? What costs are we willing to incur? Will we attempt to restore native plants and fish? The Lake Tahoe Aquatic Invasive Species Working Group believes the work this summer will help answer these questions.
For more information on aquatic invasive species, visit the Tahoe Resource Conservation District’s Web site at http://www.tahoecrd.org or call (888) TAHO-ANS ((888) 824-6267).
– Cheva Heck is a member of the Lake Tahoe Aquatic Invasive Species Working Group.
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