I love IDFG, but as a former professional film and TV producer/director, that was one of the worst videos I've ever seen! They need to hire me! Still seasick from that opening scene...ugh!

And use a different font next time--that one makes it look like they're saying there are .889 fish per mile in the downstream reaches, not 889 fish.

Is there any research of mortality rates when electroshocking and also, how often do they empty the garbage can of fish?
Seems like they miss netting a lot of the fish that get shocked. What happens to these fish?

I'm not sure how floating down a very wide river in a very narrow boat, shocking some of the fish and netting some of those--albeit twice--provides a basis for estimating fish populations. Anybody got any insight as to the scientific method here?

I'm assuming that they measure the fish because each "slot" represents a proportion of the whole population that is believed to be known, (e.g., they catch 74 fish between 16" and 20" which size range usually represents, say, 23% of the total population) though this logic seems circular.

I'm not trying to disparage IDFG or their counterparts in other states--just curious about their methods. I have long wondered how they determine the population of the great rivers, and the video raised more questions than it answered for me.

Greg Schoby, the fisheries biologist that sent me the link, said he'd be happy to answer your questions over the phone. 208-525-7290

Thanks Mel

Rainbow trout population estimates N are calculated using the Modified Petersen equation

N =[((M+1)*(C+1)) / (R+1)] – 1

Where M is the number of fish marked, C is the number of fish captured and R is the number of fish recaptured.

I didn't write it. I distilled it it from this report - http://www.southforkboise.org/wp-content/uploads/2011/07/Hebdon2006SFBdraft.pdf

The number of fish surveyed from a float boat is a very small percentage of the total. The numbers encountered using a more intensive survey technique like a canoe as part of the electro charge and a large number of people netting is higher, but you cover less water.

As a volunteer netter on one of the wading crews the fish were not in the large bucket very long. A few minutes and once the can was getting full we would pull over, count and measure. Usually someone would freshen the water. Mainly there was a focus on quickly getting the fish counted, measured and put in smaller buckets with fresh water and then walked upstream about 100 yards or so for release (that was my job). I do recall some mortality to whitefish. They seemed to be more vulnerable. Once I remember one large brown trout looked really bad and the crew worked on it and revived it. Bottom line is the IDFG crews I worked with showed concern with impacts to the fish being sampled and they pay attention to their methods. That's my take on it as a layman. But I am sure you can get good insight from Greg Schoby.

Can they do snorkeling surveys on rivers like the North Fork? Or is the water too murky?

Back in the day I worked a few summers as a tech for the Forest Service doing both electrofishing and snorkle surveys. We were working on smaller, clearer, mountain streams. We eventually switched to snorkeling exclusively because of concerns with fish mortality (we were working in Bull Trout country).

There didn't seem to be any significant difference in the quality of the surveys between the two methods. I'm not familiar with surveying bigger rivers tho... I imagine electrofishing is the only practical way to do it.