As I have previously stated, here is how SAK works. By no means am I an expert. I think it is important for the deer hunter to understand the basics and to support SAK. SAK can be very accurate as long as variables put into it are correct.
SAK(Sex-Age-Kill) is based off of the 1 1/2 yr old deer. With harvest information, formulas and scientific studies; SAK can estimate preharvest herd numbers of the prior year hunting season. By doing this and subtracting the harvest numbers, you can estimate post season numbers. By use of an expansion factor, you can predict the next season although it might not be as accurate. SAK is effective on past season numbers. Certain variables used are averages, some based on field work, and so on. Is this everything that goes into SAK, by no means. But by understanding the basics, it might help you understand the reports, studies and what the DNR is trying to say. First, take a look at the SAK report from 2008. http://dmureview.editme.com/Topic-1233889196841
Lets take a look at Unit 1. The important data is the Buck Kill, Buck Recovery Rate(BBR), 5yr Ave Yearling Buck(YB)Adult Sex Ratio(ASR), Fawn/doe ratio(F/D). I can get into how to come up with the ASR but since the DNR has it listed, no need.
The BRR is the percent of bucks killed by hunter harvest. So if the BRR rate is 60%, that means 60% are harvested by hunters and the remaining 40% is by winter, car, predition, etc.
YB is the percentage of 1 1/2 yr old buck out of the total bucks
ASR is the ratio of bucks to doe(1.59 = 1 buck to every 1.59 doe)
Doe/fawn is the ratio of fawns to doe.
For Unit 1 these figures are: Buck kill 464; BRR .60; YB .49; ASR 1.59; F/D .471
First, you need to come up with the Buck Harvest Rate.
BHR = BRR x YB = .60 x .49 = .294
So to figure out the buck population before the hunt:
Total Buck Harvest/buck harvest rate or 464/.294 = 1578 bucks prior to the hunting season
Total doe = total buck x ASR = 1578 x 1.59 = 2509
Total fawns = total doe x doe/fawn ration = 2509 x .471= 1182
Add these up and you get the total pre hunt pop of 5269....subtract the total harvest plus 15%....5269 -(1233 x 1.15) = 3851 post hunt population. (The 15% is used for wounded deer, etc.. and is a pretty good estimate).
With the post hunt population, you can figure out the deer per sqr mile. 3851/ 161 acres(this is the figure of deer range) = 24 deer per sqr mile(4 deer per sqr mile over goal(20).
(you will note the number are not exact as in the SAK report, I would imagine certain number either are rounded or the spread sheet does give the info to exact decimal.)
The SAK is vulnerable to several factors as indicated on the SAK report by Dr Boyce. These are the BRR, F/D, unit size and YB, to name a few. BRR and F/D estimates can influence the model greatly. We've never seen how the biologist come up with BRR and not sure enough field work is done on the F/D. To give an example on how BRR can adversely effect the population lets increase it to 70%.
.7 x .49 = 0.343 BH of 464/0.343 = 1352 buck pre harvest(decreased from 1578). 1352 bucks tx ASR(1.59) = 2151 doe.....2151 doe tx F/D(.471) = 1013 fawns. Total pre hunt population is 4516 rather than 5269. Subtract the harvest data...4516 -(1233 x 1.15) = 3098 post hunt population. Remember how important "goal" is? Well, take 3098 and divide the 161 acres....19.24 deer per sqr mile...below goal. This is a large difference so it is really important the BRR is accurate. If it's not, we could have a higher quota in 2009 on a herd that may already be "at goal".
What can a hunter do to help? I'm probably one of the biggest problems here. I never liked the DNR aging deer, hated the large smiley deer face and didn't know why it was neccessary. Well, it is important for SAK to have as much of this info as possible. The more data they have, the better SAK will work. So I'd ask every hunter to make sure their deer is aged. Ask the DNR where he'll be 2nd weekend so you can bring your deer to him to be aged(good luck with that...lol).
As for the BRR and F/D, continue to ask questions. We need to know the factual data going into these figures. Without this, SAK could be manipulated. Michigan uses SAK but they take out some of the BRR.
The big picture is, SAK can work. We just need more input and less often changed variables. I hope this info will shed some light on the SAK report: http://www.dnr.state.wi.us/org/land/wildlife/hunt/deer/SAKreport.pdf