This is of course, an oversimplification. Conditions vary greatly from stream to stream with respect to stream size, length to barrier, rate of warming, rate of returns, flows, angling pressure etc. Still, gathering and validating that general picture certainly helps clarify our understanding of just what does tend to happen from year to year over the course of the returns.
Probably one of the best data sources to use with respect to that typical run picture is the Minnestota DNR's French and Knife River trap data. The traps intercept up bound fish and the data is captured in real-time. The numbers themselves from year to year aren't of primary importance to the Creel Project run picture; but the start, peak and overall length create a visual signature we can use to compare year to year results. The following is a pretty good example, hopefully it will clarify what we're talking about:
For now, ignore the red Population line. More about that in a minute. What we've done here is to filter out the actual numbers captured, what we're interested in getting at is the shape of the blue line over time. You're looking at the actual combined French and Knife trap results from 2012. This includes both Kamloops as well as Steelhead.
Very generally we see a start point the week of March 19th, in reality this is a zero point as no fish were actually captured. The run initiation temperatures were reached between March 24th and March 26th. Rainbows began upstream migration in their greatest numbers, and returns peaked the week of March 26th. Subsequent to that point, returns to trap tapered off with the last fish captured the week of May 7th. May 14th was the end with no fish captured that week and is again a zero point.
So is this what a "typical" run literally looks like? Consider the evidence: We have numerous years of trap data to compare against, both in terms of unique trap (French vs. Knife) as well as combined trap. What the data tells us so far is that returns to trap tend to peak within the first 7-10 days of the Lower Shore index stations reaching initiation temp thresholds. While the temp numbers previously were an aggregate average based upon several index stations, we now have temp data available specific to the Knife River. We will use that data in 2014 to compare against Knife River trap data to get a more accurate picture. The problem with the older data was that the index streams were all smaller than the Knife, and tended to warm far more quickly. Because of that we did not know for sure when initiation temps were reached on the Knife, but it was pretty close...
So far, the vast majority of the trap data looks very similar to what's depicted above. So similar in fact that we are confident, at least for now, that this probably is the typical run picture: A sharp peak immediately post-initiation threshold followed by approximately 4-6 weeks of subsequent returns albeit at much lower levels. The current assumption is that this picture applies across all regions of the Shore. But of course, we didn't stop there. We also wanted to use the Creel Project to see what the angling side of the picture looks like, and whether or not it validated the so-called typical run picture. Here's what we've found so far-
Using all four years of project data, and comparing Lower to Lower, Mid to Mid, and Upper to Upper Shore data, the creel data shows a very similar picture of the progression: A sharp increase in returns immediately post-initiation temps, a peak of approximately 7-10 days, and returns tapering off but continuing for an additional 4-6 weeks. The difference between this signature and the trap signature lies in the fact that it's not a single point-source like the trap(s) is/are. Fish are also sampled from all portions of the streams.
The other point to consider is the effect of in-stream populations of fish on the run progression/signature. We think the creel project signature is a little fatter because fish tend to remain in the stream for some period of time; we just don't know precisely what that time period is. We know from the scientific literature that down bound adults have been re-captured up to 60 days after initial up bound capture on the Knife. This probably is on the extreme end of length of stay in the stream as most North Shore streams are smaller and warm more quickly overall. The fish enter, do their business, and then leave more quickly; but they still likely stay for a number of days.
One thing we did (and this was art/guessing on our part), was to use various in-stream population models to see what the effects of various length of stays (1 week, 2 weeks etc.) did to the trap signature. If you look at the 2012 trap numbers above, we ran various population models to try and compare against what we were seeing in the Lower, Middle and Upper Shore signatures. What we found was that a 1 week population model (80% adult fish remaining in-stream for at least 7 days) gave us the closest signature to the creel signatures from a run-picture/progression standpoint. We still don't quite know if this is significant, but it does suggest that adult fish remain in the streams for around 5-7 days while doing their thing. Or we could be completely wrong, more data needed.
All of this information is useful. Minnesota Steelheader tracks in-stream conditions on an annual basis for each region of the shore. We typically post what those conditions are generally for each region without posting specific streams. If you see that initiation temps have been met and know roughly how long they've been above that point, you can use the charts to do a little planning regardless of where you want to fish on the North Shore. If you can get out and fish every day, probably not as important. If you have to plan and travel, this information becomes a great tool; but YOU still have to make the decision about which region to fish, which stream, which presentation, which bait or fly.
So that's what we have for now, we're not married to the data or the conclusions. As more information comes in we'll continue to update, consider, analyze and modify.