Chena River Chinook Salmon Study » Field Work Reports

Four-day data collection float

Jason — Sat, 02 Aug 2008 09:13:11 +0000

It’s been a while since the last update, because we’re all out on the river all the time, or in lab processing samples and tinkering with equipment. We’ve all had our setbacks but the project is generally going well.

From July 24th to the 27th, I floated 50 miles of the Chena in a cataraft. I stopped in prime locations to shoot stereoscopic, high-definition digital video of foraging juvenile Chinook salmon, which I’ll use to analyze the ways that habitat and competition affect their foraging success. It took months of trial-and-error customization of the video equipment, but I finally got many hours of ideal footage for my analysis. This post simply chronicles the trip, and the fish footage will take a while longer to process, but you can expect to see it on the website soon.

The raft fit all my gear… barely.

Much of it gets unloaded at every data stop:

I spent a lot of time at huge logjams, which seem to be the most important Chinook habitat on the upper Chena. At this one, the fish live deep in the back of the logjam:

Here’s more Chinook habitat. The orange flag marks the top of the handle pole on my camera mount.

Spending 72 hours on the river allowed me to both better absorb the “big picture” and pick up on some little details I might otherwise have missed. For example, I learned that many juvenile Chinook are now venturing far from cover to feed late in the evening, either because they’re safer from predators or because there’s enough food to justify the risk (or both). This isn’t completely unexpected, but such behavior was seemingly absent early in the summer when the fish were smaller, and the timing of its development may be worth further study. Here’s a photo from one such site, where the fish were surface-feeding on tiny midges:

It’s hard to spend so much time on the Chena without some golden photo opportunities, and I didn’t pass them up. Enjoy the moose, eagles, baby mink, and scenery:

Underwater Video of Juvenile Chinook

Jason — Sun, 20 Apr 2008 09:35:40 +0000

Underwater video is going to play a huge role in Megan’s and my projects. Last fall we went out and tested the first and simplest of several video cameras we’ll be using, an Aqua-Vu DVR made for ice fishing, which I’ll be setting up with auxiliary batteries to do lengthy surveillance of juvenile Chinook schools. We found some salmon in a very large, dense logjam and shot these videos:

This year we’ll be using higher-quality cameras in stereoscopic setups to do 3D analysis of fish lengths and positions, utilizing and advancing the methods described in these two papers:

Hughes, N. F., Hayes, J. W., Shearer, K. A., & Young, R. G. (2003). Testing a model of drift-feeding using three-dimensional videography of wild brown trout, Salmo trutta, in a New Zealand river. Canadian Journal of Fisheries and Aquatic Science, 60(12), 1462-1476.

Hughes, N. F. & Kelly, L. H. (1996). New techniques for 3-D video tracking of fish swimming movements in still or flowing water. Canadian Journal of Fisheries and Aquatic Science, 53(11), 2473-2483.

The Chena from a Helicopter

Jason — Sun, 20 Apr 2008 07:58:42 +0000

Back on August 2nd, Sam Decker did a helicopter flyover on the Chena to count and map adult Chinook salmon redds. I rode along to take photos of the spawning sites (and other interesting features) from the air. Because I synced the camera’s clock with the clock on my GPS, a little post-processing enabled me to place all the pictures precisely on a map. You can browse the interactive map at Flickr.

Here are some highlights. Notice the spawning Chinook on their redds in the top/middle picture, and the large woody debris piles in the pictures on the right, which seem to be especially important habitat for juvenile Chinook.

We’re using these photos right now, along with plentiful GIS data about fish abundance, to narrow down our potential study reaches for this summer.