Largemouth bass and bluegill, fish that might normally be found in a Midwestern lake, are thriving and spreading around Lake Tahoe in a situation that could be accelerated by a warming climate.
Those are among the conclusions of a new study of warm-water fish that live in the Sierra lake and the threats they could pose to its sensitive ecosystem.
“The most important findings from our study indicate that the warm-water fishes of Lake Tahoe are either competing (with) or preying upon native fishes,” said Sudeep Chandra, an assistant professor and fish expert from University of Nevada, Reno.
“It is likely that climate warming will increase the spread of invasive fishes,” Chandra said. “Through increased warming of temperature near shore, Lake Tahoe’s waters will come well into the range that allows these fish to spawn in the lake.”
The good news, Chandra said, is that fish densities monitored during the three-year study that started in 2006 are low in most locations. That suggests that if steps are taken now to manage those fish, changes may be possible “before they get out of control.”
The $62,700 study, presented in early July to the Nevada Division of State Lands, primarily examines the status of the most common warm water fish living in Tahoe — largemouth bass and bluegill.
Among other things, research involved snorkelers surveying fish populations, shocking fish so researchers could determine their length and weight, and dissecting fish to analyze their diets.
The fish, first noticed at Tahoe in the mid to late 1970s, were likely introduced illegally by anglers eager for a new type of fish to catch, the report said.
Tahoe’s fish population had already been vastly altered by people. Mackinaw, rainbow, brown and brook trout were all introduced to the lake. The Kokanee salmon that run up Taylor Creek every fall were introduced to Tahoe in the 1940s.
Competition with Mackinaw contributed to the extinction of Tahoe’s native Lahontan cutthroat trout in 1939.
More recently introduced warm-water fish bring their own problems. In South Lake Tahoe’s Tahoe Keys, where populations are thickest and temperatures warm enough for the fish to spawn, native minnows have virtually vanished, experts said. The Keys are also where an invading aquatic weed, Eurasian watermilfoil, grows thickest, providing attractive habitat for the fish.
While the bass and bluegill are most common at the Keys and other marinas and partially enclosed bays where the water is warmer, evidence suggests they are moving.
As part of the study, electronic transmitters were implanted in bluegill and largemouth bass that were then released in the Keys. Radio signals indicated several of each type of fish swam out the marina’s channel and into the open lake before contact was lost.
“That could mean they are spreading around the lake to other suitable habitat,” said Ka Lai Christine Ngai, a researcher from the University of California, Davis Tahoe Environmental Research Center.
“They can move around the lake and get to other suitable pockets,” Ngai said.
Preservation of native minnows is an important ecological goal at Lake Tahoe, and determining the threat posed to them by invading warm-water fish is a needed piece of information, said Elizabeth Harrison, water quality program manager for the Nevada Division of State Lands.
“We’re obviously trying to maintain the native fisheries that are there,” Harrison said. “Until we get a good handle on this, it’s hard to determine the best way to move forward.”
If the fish proliferate in number, they could affect Tahoe’s diminishing clarity by boosting algae growth with nutrients excreted into the water, Chandra said.
Largemouth bass eat crayfish, which were also introduced by humans into Tahoe and established there by 1936. The lake’s crayfish, which Chandra said may now number more than 200 million, can contain large quantities of phosphorus. When the bass eat and excrete crayfish, the released phosphorus could fuel additional algae growth in Tahoe’s waters.
The large number of crayfish in Tahoe could provide a ready, untapped food source for bass that could help boost their numbers, experts said.
“If we do not begin to manage populations, especially source populations such as the Tahoe Keys, then it is likely their densities will increase and result in more stress to Lake Tahoe’s native biodiversity and possibly impact clarity,” Chandra said.
While the bass and bluegill are most common at the Keys and other marinas and partially enclosed bays where the water is warmer, evidence suggests they are moving.
As part of the study, electronic transmitters were implanted in bluegill and largemouth bass that were then released in the Keys. Radio signals indicated several of each type of fish swam out the marina’s channel and into the open lake before contact was lost.
“That could mean they are spreading around the lake to other suitable habitat,” said Ka Lai Christine Ngai, a researcher from the University of California, Davis Tahoe Environmental Research Center.
“They can move around the lake and get to other suitable pockets,” Ngai said.
Preservation of native minnows is an important ecological goal at Lake Tahoe, and determining the threat posed to them by invading warm-water fish is a needed piece of information, said Elizabeth Harrison, water quality program manager for the Nevada Division of State Lands.
“We’re obviously trying to maintain the native fisheries that are there,” Harrison said. “Until we get a good handle on this, it’s hard to determine the best way to move forward.”
If the fish proliferate in number, they could affect Tahoe’s diminishing clarity by boosting algae growth with nutrients excreted into the water, Chandra said.
Largemouth bass eat crayfish, which were also introduced by humans into Tahoe and established there by 1936. The lake’s crayfish, which Chandra said may now number more than 200 million, can contain large quantities of phosphorus. When the bass eat and excrete crayfish, the released phosphorus could fuel additional algae growth in Tahoe’s waters.
The large number of crayfish in Tahoe could provide a ready, untapped food source for bass that could help boost their numbers, experts said.
“If we do not begin to manage populations, especially source populations such as the Tahoe Keys, then it is likely their densities will increase and result in more stress to Lake Tahoe’s native biodiversity and possibly impact clarity,” Chandra said.