“The View from Above Nimbus”

By Kat Perkins

Nimbus Basin on a sunny October day.

Over the past year, I’ve spent almost 1,000 hours looking at aerial photos of the lower American River, counting redds. In addition to staring at these gorgeous aerial photos to map spawning, I have been taking a closer look at the method we use to make redd counts. With the help of folks at Cramer Fish Sciences, I was able to get a better picture of how repeatable aerial redd counts are and how we can improve the accuracy of our counts. It turns out that the process is almost as much an art as a science: the decision to count a feature as a redd is subjective, and the more familiar you are with the river the more likely you are to make good decisions.

One recommendation to improve accuracy that came out of this research was that the technician performing counts should visit the river to monitor spawning on the ground. Since I’ll be doing counts again this year, that means I get to visit the river, search for salmon, fly a drone and call it work! After looking at the river in two dimensions for so long, it’s really exciting when I get to actually experience it.

This past Sunday, I met Bureau of Reclamation scientist John Hannon at Nimbus Basin to monitor early spawning. I found John at the edge of the parking lot. “There’s a lot of fish out there!” he said. Looking out I could see fish jumping out of the water. But were they spawning yet? Probably not, since it’s only mid-October and water temperatures at the dam release have just recently been hovering around 62 degrees, but we’d have to look a little closer on foot and with the drone to know for sure. John grabbed the drone out of his car and then we made our way down to the water.

When we got to the side channel, John asked if I minded getting my feet wet. “No!” I answered enthusiastically, and we waded into the water. I pointed down the side channel to where there had been rocks piled to make a dry crossing and explained that I’d spent most of Friday moving these rocks. John was happy to know that, since he’d noticed that the walkway was blocking the side channel off for fish and had pointed this out to Lilly who’d sent me out to the river. While pretending to be a human bulldozer (just call me Katerpillar) I watched a fish swimming through the deeper part of the side channel and wished I had the salmon equivalent of traffic signage to let my new friend know the road would soon be clear for fish passage.

At least one “slam-dunk”, totally unmistakable redd is visible in this photo, at the upper end of the side channel.

Upstream from where John and I crossed through the side channel, we could see a redd through the water. In aerial photos, redds show up like white polka dots against the dark river bed. On the ground, the light rocks the salmon uncover while building their nests almost glow through the water and you can see the “pot” of the nest the salmon has excavated. When we got to the edge of the last little island in the basin, we saw one more redd and a fish guarding it. We could also see that there were two fishermen, and on the other side of the basin, a Fish and Game officer.

This year, Nimbus Basin is closed to fishing. This was bad news for these two fellows, but good news for fish and, in the longer term, fisherfolk. The Hatchery plans to reorient its fish ladder into the Nimbus Basin and remove the weir, and that’ll open more prime spawning and rearing habitat to fish. Fewer people in the basin also means that we can more safely fly our drone to monitor spawning.

There are already a lot of fish in Nimbus Basin, visible in this drone photo as dark spots.

From an open spot on the other end of the basin, John launched the drone and flew a grid across the basin. We could see lots of little of black ovals – fish! But not many redds. After checking Nimbus, we visited Sailor Bar and Sunrise.

John flew the drone again at both Sailor and Sunrise. Usually John would just bike along the Parkway bike path and look out for fish but this year he’d promised photos of any early redds to a researcher at NOAA, who is investigating the effectiveness of redd monitoring using a drone. He had planned to conduct his research on upper tributaries to the Sacramento, but because of worries about how the fires would impact water quality the study site was relocated. The circumstances are tragic, but it is exciting for us to have more eyes on the American, and to participate in more cross-agency collaboration and learning.

John catches the “bird” mid-air after flying Sunrise.

John has been visiting the river to monitor the beginning of fall run Chinook salmon for many years. Knowing how the run is progressing helps him make decisions about scheduling the flights to capture aerial photographs of the whole river. We’ve been using these aerial photos to perform redd counts since 1991, and this relatively long-term data set is an incredible resource.

This is only my second year witnessing the salmon return, but I can’t imagine that this season becomes any less exciting the more times you’ve experienced it. In fact, the more I know about our river system, the more interesting it is. There are so many factors that converge to make the run what it is, so every year is unique – yet, we can also pick out patterns, and understand how to better manage and monitor.