In 1984 when Eurasian Watermilfoil was first noticed by the Tahoe Divers Conservancy, divers easily could have hand-pulled all of the weed up, nipping in the bud what was to become an explosive bio-invasion. Regrettably, this was not done, and invasive species have propagated throughout Lake Tahoe and working its way throughout the Truckee watershed.
<ul><li>Underwater, A Disturbing New World </li></ul>FUTURE OF THE LAKE
Shifting Ecosystems <ul><li>The Tahoe Divers Conservancy was formed by local divers in because of their concern that the aquatic ecosystem of Lake Tahoe is being neglected. </li></ul><ul><li>Having first focused on pollution and garbage, they have expanded their mission to climate issues and now the serious threat of invasive species. </li></ul>
<ul><li>When the divers are asked by tourists, </li></ul><ul><li>“ What do you see under there?” the most common response by divers is “ not much ”. </li></ul>
<ul><li>Diving among beautiful waves of granite boulders the size of houses with bright reflections of light from mica studded sandy lake bottom presents a generally stark but surreal crystal environment. </li></ul>We describe diving in the Lake Tahoe as Zen Diving .
<ul><li>Now the underwater world of Lake Tahoe is disturbingly full of strange, new life. </li></ul><ul><li>In just a few years, vast sandy nearshore that for centuries covered the bottom of Lake Tahoe have disappeared under a carpet of invasive plants. </li></ul><ul><li>This change is not merely cosmetic. </li></ul>
<ul><li>Invasive species will upend the ecology of Lake Tahoe, shifting distribution of species and starving familiar fish of their usual food supply. </li></ul><ul><li>Eurasian watermilfoil, Curlyleaf Pondweed and the Asian Clam are all now found in Lake Tahoe. </li></ul>
<ul><li>And it is not just invasive plants. </li></ul><ul><li>This summer scores of Brown Bullhead Catfish were found in Emerald Bay. </li></ul><ul><li>Once confined to the Tahoe Keys and Taylor Marsh, non-native fish are propagating all over Lake Tahoe. </li></ul>
<ul><li>Signs of the shift will be hard to ignore in the future. Mats of dead, smelly plants are already washing ashore on Lake Tahoe’s beaches, castoffs of a vast underwater expanse. </li></ul>Multiple strains of E. coli bacteria and botulism spores will thrive in the new underwater garden, contributing to beach closings and the widespread deaths of migratory birds.
<ul><li>Fishermen will take notice that the lake trout, salmon and other fish will get skinnier each season. </li></ul>
<ul><li>How widely will the impact will be felt? </li></ul><ul><li>Is Lake Tahoe changing faster than </li></ul><ul><li>the researchers can study it? </li></ul>After Before
<ul><li>Lake Tahoe may adapt as it has in the past, from man’s intervention in the natural processes, such as logging and well meaning but destructive introductions of Lake Trout, crayfish and mysis shrimp. </li></ul><ul><li>But the invasive species are fueling change in the lakes at a rate far faster than we have ever seen. </li></ul>
<ul><li>Having dove and trained in the Great Lakes over the past decade and have witnessed the changes first hand, the Tahoe Divers Conservancy doesn’t necessarily know all the impacts, but we have seen enough to know that they are going to be catastrophic to the lake environment and to the regional tourist industry. </li></ul>
<ul><li>Is the ecological balance of Lake Tahoe </li></ul><ul><li>at a tipping point? </li></ul>Can we act quickly enough to help it recover? Can the Lake recover?
<ul><li>None of the key species leading the change—like Eurasian Watermilfoil—are new arrivals. </li></ul><ul><li>The zebra mussel famously invaded Lake Michigan two decades ago, and its cousin, the quagga mussel, wasn't far behind. </li></ul>
<ul><li>But in the last two years the Eurasian Watermilfoil has taken off with alarming speed, exploding across the lake floor. </li></ul><ul><li>Quickly followed by Curleyleaf Pondweed, which we only saw colonizing a season ago, spreading throughout the south-shore of Lake Tahoe growing to four feet in height. </li></ul>
<ul><li>And all this while the greatest threat to Lake Tahoe and the Western States is knocking on our front door with the quaggas and zebra mussels, which like to attach themselves to rocks and man-made structures and can colonize sandy bottoms deeper in the lakes. </li></ul><ul><li>Between them, the species filter lake water ceaselessly, making it so crystal clear that light can penetrate far deeper than before. </li></ul>
<ul><li>Together, these species can not only alter the clarity of the water but also devoured and filter out the nutrients that use to sustain species at the base of the lake's food chain, starving what larger fish are left. </li></ul>This change may allowed native species of algae to run rampant. In the Great Lakes algae species once relegated to shallow waters can now grow in 30 feet of water, twice as deep as a decade ago, its waving tendrils now cover vast offshore areas.
<ul><li>Prior to large changes in the lake environment, Lake Tahoe’s aquatic ecosystem was relatively simple for thousands of years. </li></ul>Unfortunately, Lake Tahoe ceased to be a wholly native ecosystem long ago.
<ul><li>However, by 1939 cutthroat trout were extirpated from Lake Tahoe, and a large lake trout ( Salvelinus namaycush ) population replaced them as the top predator. </li></ul>Beginning in the late 1800’s, species introductions combined with logging for mining started to alter the lake’s ecology. The native food chain was dominated by a single predator, Lahontan cutthroat trout ( Oncorhynchus mykiss ) that fed primarily on pelagic tui chub ( Siphateles bicolor pectinifer ) and zooplankton.
<ul><li>Crayfish ( Pacifastacus leniusculus ) were introduced multiple times to Lake Tahoe and established by 1936. Found in large numbers 55 million in the late 1960’s and 65-75 million by early 2000. </li></ul>After the introduction of Mysid shrimp in the 1960’s, again there was a shift in Lake Tahoe’s again the food web structure. After Mysis establishment the annual length and weight of returning spawners decreased.
<ul><li>Finally, in the mid to late 1970’s and again in the late 1980’s, a variety of nonnative species were found in the nearshore environment. </li></ul><ul><li>These warmwater fish introductions were illegal. </li></ul><ul><li>Up to this point warmwater fish species were rarely found while native minnows remained abundant. </li></ul>
<ul><li>The change in fish structure was substantiated by fishing guides operating out of the Tahoe Keys. </li></ul><ul><li>Within a decade they could no longer collect minnows commonly used as bait during fishing charters on the lake. </li></ul>By the end of the 1980’s, largemouth bass ( Micropterus salmoides ) were common while redside shiner and speckled dace populations declined or were virtually eliminated from the Tahoe Keys.
<ul><li>Also, bass found in the nearshore often correlate with the presence of the nonnative plant species, water milfoil ( Myriophylum spicatum ) which produces favorable habitat for these fish. </li></ul>Preliminary studies conducted around the lake by the University of Nevada-Reno and the UC Davis, Tahoe Environmental Research Center in 1999, 2003, and 2006 demonstrate that 50% of these sites contain nonnative, warmwater fish species.
<ul><li>What will the new aquatic order be? </li></ul><ul><li> The Great Lakes the food chain, as it was known, is gone. To be exact, “a new food chain has settled”, said Brenda Moraska Lafrancois, aquatic ecologist in Minnesota with the National Park Service. </li></ul>From 20 deep feet of water out to 40 feet or more, mussels cover the lake floor in a crunching layer as brittle as breakfast cereal. On their shells fronds of algae wave in the water, forming a carpet the lush green of a tropical forest.
<ul><li>In dives in the Great Lakes and specifically off the shores of Milwaukee, divers enter the shoreline stepping over razor sharp shells of the quagga mussels, slicing hard rubber reinforced booties. </li></ul><ul><li>We saw families laying thick canvas tarps on the beach to picnic on, to spare the kids from the sharp shells. </li></ul>Swimming in tennies was the attire du jour.
<ul><li>We just can’t fathom that scenario at Lake Tahoe. </li></ul>
ACTION PLAN <ul><li>The Tahoe Divers Conservancy propose a simple, cost effective - THREE POINT ACTION PLAN </li></ul><ul><li>ASSESSMENT </li></ul><ul><li>CONTAINMENT </li></ul><ul><li>REMOVAL </li></ul>
ASSESSMENT <ul><li>ASSESSMENT - Collect existing data and perform a lake-wide diver survey that will give a comprehensive overview of the existing and potential problem and the resources that may be needed to address the problem. </li></ul>
CONTAINMENT <ul><li>CONTAINMENT - The assessment will provide crucial data to formulate an independent plan for which areas can be contained and for those areas that containment may be unrealistic given the resources available. </li></ul>
REMOVAL <ul><li>REMOVAL - Using the Tahoe Divers Conservancy resources and developed technology, immediately execute a removal and containment action plan for Lake Tahoe on a year around basis. </li></ul>