Clear view

People who’ve read news coverage of the 2019 State of the Lake report from the Tahoe Environment Research Center probably also heard about one of its highlights—a program geared toward removing a tiny, non-native shrimp species called Mysis shrimp (or Mysids) from the lake, with the aim of improving its famed clarity.

According to the TERC website, the shrimp were purposefully introduced to the lake from 1963-1965 by the California and Nevada Departments of Fish and Game. The idea was that they’d provide a plentiful food supply for lake trout, Tahoe’s main sport fish. Unfortunately, this didn’t happen. By 1971, the shrimp were well established in the lake. But rather than being eaten by fish, they Mysids were eating the fish’s main food source—native zooplankton species called Daphnia and Bosmina—at night and hanging out deep in the dark to avoid fish during the day.

How does this relate to clarity? In 2011, TERC researchers discovered that the Mysis shrimp had largely disappeared from Emerald Bay, and, as native Daphnia and Bosmina had rebounded, the bay’s clarity had improved drastically.

The Mysids later returned to the bay. In 2018, TERC began a pilot program to remove them by night trawling with a huge net. When the program wraps up next year, they’re hoping to have more thorough data documenting the relationship between Mysids, zooplankton and lake clarity. In the meantime, those wanting to learn more about these tiny species that have such a big impact on the lake can head up to TERC’s Tahoe Science Center on the Sierra Nevada College campus in Incline Village.

“We do have some preserved samples of mysis shrimp in the education center, as well as video footage,” said Program Manager Alison Toy. “They are the ones that we’re trawling off the lake. We actually have been freezing cubes of Mysis shrimp, and we do feed them to the fish that are in our Tahoe Science Center in Incline Village as well as our Tahoe City Field Station.”

At the center, Toy said, visitors can learn about “the environmental timeline of the shrimp—when they were introduced, the effect on the lake, and also the ongoing research that’s been happening.”

“We have pictures available,” she said. “We also have live specimen of the Daphnia. And the Daphnia is actually the target zooplankton that we’re trying to restore the population of.”

According to Toy, it’s the Daphnia that researchers believe has the greatest effect on lake clarity.

“The Daphnia are like indiscriminate little cows that swim around Lake Tahoe, and they’re just pretty much, like, mouths open and eating everything—including these really small diatoms, these small, single-cell algae that we have … as well as potentially fine particles that are all floating in its path. It’s just kind of taking everything out. Visitors can also see a two-thirds scale model of the boat researchers will continue to use to trawl for Mysis shrimp during the program’s final year.

“We’re definitely hopeful, and I think with another year we might be able to more conclusively say,” Toy said. “This is only being done in Emerald Bay right now. It’s kind of like an in-lake experiment. But if it works out, then this is definitely something that we’ll look to apply to the entire whole of the lake.”