First, some adult Chinook resting on their way up the North Fork of the Chena:

Juvenile Chinook feeding:

Juvenile Chinook versus the shockwave from an airboat:

All the videos are much lower-quality than the originals due to YouTube’s high file compression. To get a sense of the original HD video, here are some full-resolution stills captured from the HD video. Click a picture to see it full-sized.

Adult Chinook in the North Fork of the Chena, with a grayling and a whitefish in the foreground.

Juveniles foraging in the North Fork:

And in the main stem Chena:

Each of these videos and stills comes from a pair of side-by-side Sony HDR-SR12 video cameras in underwater housings with special wide-angle ports. Using two fixed cameras and some calibration equipment allows us to analyze the positions of these fish in 3D on the computer. That enables us to precisely measure their lengths, feeding positions, spacing, and many other scientifically interesting attributes.

Baited minnow traps and unbaited snorkelers were used to count fish. Interestingly, the snorkelers were far more successful in the spring than the minnow traps, and were almost useless in the fall. They were cold both times, and whined occasionally throughout.

Because these different counting methods are not equally effective, it’s more useful to compare the patterns of distribution between spring and fall than the actual number of fish found at each site. Remember, these are raw counts, not estimates of the total fish population at the site.

Spring (trap + snorkel counts):

Fall (traps only; snorkel counts were negligible):

In the lab, these data are being cross-referenced with other relevant numbers, like aerial redd counts. Those maps will get posted later. The most evident pattern is a downstream shift in distribution in the fall. A few of the several hypotheses to explain this pattern include:

1. The slightly warmer temperature downstream is more favorable for growth.
2. The lower water clarity downstream offers more protection from predators.
3. A major mid-summer flood carried most surviving fish downstream.

The study will hopefully reveal which of these (if any) explains the downstream shift.

Update August 1, 2008. New observations suggest there may not actually be a downstream shift.  We used the same methods and sampled similar habitat in the upper and lower river in 2007, but lower-river fish may be more inclined to utilize that habitat than upper-river fish.  We don’t have conclusive proof either way, but this possibility is noteworthy.