Fishing Throughout History: Tahoe’s Ever-Changing Ecosystem As Indigenous Numbers Decline
Lake Tahoe has changed over the years and this change becomes evident when looking at the lake’s food web.
Due to overfishing, the introduction of non-native species (both intentional and accidental) and high water temperatures, the lake essentially has a new ecosystem. And although all but one native species still exist in the lake, their numbers are dwindling.
“Before things were introduced, Lake Tahoe had a very simple food web,” said Dr. Sudeep Chandra, professor of biology at the University of Nevada, Reno. “There were about 12 types of invertebrate orders… maybe as many as 18 but not many.”
A look at the food web from the 1800s shows the Lahontan Cutthroat Trout atop the Offshore Fish Range – fish that hang out far from shore. Underneath are the tui chub and the mountain white head.
These offshore fish feed on zooplankton and benthic macroinvertebrates, or inhabitants of the seabed, which feed on phytoplankton, plants and coastal algae.
Feeding on zooplankton and benthic macroinvertebrates, coastal and groundfish consist of speckled dace, Paiute sculpin, Lahontan red coast, and Tahoe sucker.
Chandra, who specializes in restoring native species and managing non-native species, said there are around two to six native plants, so overall it’s not a complex food web.
However, over the years the ferocious population began to decline.
“These were basically commercial cutthroat trout fisheries in the late 1800s, harvesting more fish than the population could handle,” said Brant Allen, a biologist at UC Davis, Tahoe Environmental Research Center. “So, with the cutthroat trout dwindling, they started looking for other species of game fish that could replace them.”
Between the 1800s and 1900s, rainbow trout, speckled trout, brown trout, and lake trout were all introduced to the lake.
The introduction of lake trout, also known as mackinaw, marked the end for cutthroat trout. Mackinaw had become established in the lake in the late 1910s and by 1940 cutthroat trout had disappeared from Lake Tahoe.
Sarah Hockensmith, director of outreach at the Tahoe Institute for Natural Science, studied natural resource management. She is avid angling and has caught many non-native Tahoe fish, but still prefers these species not to be introduced.
“Never in the history of anything has the introduction of a non-native animal into a habitat been a good thing,” Hockensmith said. “So it’s really important to remember that sometimes people have good intentions and that’s why it’s so good to rely on data and science and what is natural to make good decisions, because if you are just trying to fix a problem or do something beneficial for humans by introducing a non-native species or trying to correct it with another non-native species, it will usually lead to failure. Especially in this habitat or within this ecosystem.
Allen said there have been efforts in lakes across the country to find a way for Mackinaw and Cutthroat to live in harmony and that there has yet to be success.
“There have been some improvements, but I wouldn’t say it’s been a success yet,” Allen said of an effort at Yellowstone Lake. “And the reason they spend so much time, energy and money trying to eliminate the lake trout is because it is the cutthroat predator, when it was placed in the cutthroat. essentially disappeared. And so this story has been told in several places, not just in Tahoe. “
Efforts have been made to reintroduce the cutthroat into the watershed, and although this has not been successful in the lake, there have been successes in the alpine lakes around the basin.
Between 1888 and 1936, crayfish were introduced to the watershed surrounding Tahoe, to be a food source for humans. However, they found their way into Tahoe and with no real predators they settled down and grew to large sizes.
“The number of crayfish has more than doubled since they were first estimated in the 1960s when shrimp were first introduced and we believe they are doubling because now trout are not. ‘feed more of them and they are practically able to grow taller,’ Chandra said. .
During the winter, they migrate from shorelines to deeper waters, eating any native plant species near the shore along the way. Additionally, Chandra said the crayfish likely ate the eggs of native littoral fish.
In addition to the various trout that were introduced, Kokanee salmon were accidentally introduced in the 1940s. A salmon hatchery in Tahoe City overturned, allowing Kokanee to enter the lake.
“They were kept in the lake by artificial spawning and egg farming in Taylor Creek,” Chandra said. “They wouldn’t survive in great numbers if we didn’t have the Taylor Creek fall fish run. “
In the 1960s, mysis was introduced to the lake as a food source for lake trout. Even though it was done intentionally, it was a mistake the basin still faces today.
Mysis shrimp have large, sensitive eyes so during the day they migrate to the depths of Tahoe, out of reach of trout. Not only are they not a good food source, but they also feed on native zooplankton, Daphnia and Bosmina, two species that feed on algae.
In addition, these two species of zooplankton are excellent sources of food for Kokanee.
“The first UC Davis research in the 1970s shows that Kokanee spawning numbers plummet after shrimp are introduced because food is gone and Kokanee’s size has increased from about 50 centimeters to about 2 feet up to 35 centimeters, so just above a foot, ”said Chandra.
Although all of these species are examples of intentionally introduced species, starting in the 1980s several species were accidentally introduced, including warm water fish like bass and bluegill.
Goldfish have also been introduced by people dumping aquariums into the lake, and species like the curly-leaved pondweed, Asian clam, and Eurasian water milfoil have hitchhiked on boats and established themselves in the lake.
There have been several efforts to eradicate these species and recent efforts, such as bubble curtain and ultraviolet boats, have had some success. The Tahoe Regional Planning Agency has implemented boat inspections to prevent other non-natives from hitchhiking.
But when it comes to larger species, like lake trout, Hockensmith said it was impossible to eradicate them.
Allen said there was a philosophical debate over whether to eradicate these species, if at all.
“There were the cold water game fish species that were introduced like trout and Kokanee, rainbows and browns; these have been touted as sanctioned introductions by resource agencies, the California Department of Fish and Game and Wildlife, ”Allen said. “And they provide a great recreational aspect to the lake and there is a huge economic component. “
There are businesses such as sporting goods stores and fishing tours that have built their business around these fish. In turn, these companies bring in a lot of tourist dollars in the basin and contribute greatly to the local economy.
And there are other positive benefits. Hockensmith said osprey populations were able to nest in Tahoe for the first time because they can easily catch rainbow trout or warm water fish.
“It’s interesting to see the balances of these non-native fish and how other opportunists like these other native animals, like bears and raccoons, can take advantage of them,” Hockensmith said. However, she added in the scheme of things, it is still bad.
Chandra said that of all the native species found in the food web of the 1800s, the only thing missing today is throat cut.
“The native fish are still in the lake, still in the streams, but they have increased tenfold since the 1960s,” Chandra said. “They are in pain.
Scientists are studying the problem and finding solutions and raising awareness can help prevent people from making the problem worse.
Chandra said: “This is an absolutely critical time to tell people the story of ‘your native species are still here, but we are not protecting them as we should be” and then we have to figure out what is causing the decline. “