SAK method of population estimating

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SAK method of population estimating

Postby Fish » Wed Feb 25, 2009 8:30 am

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. 

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 

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:

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RE: SAK method of population estimating

Postby Fish » Wed Feb 25, 2009 8:31 am

When I first joined this forum two months ago, I was searching for others, like me, who were upset with the 2008 deer season.  I was angry and looking for answers.   I never thought I'd be where I am now.  Many people ask me the same question, why?  I look back at my time afield with my father and grandfather, that special feeling walking up to their deer and helping drag.  I told both of them about the pregnancy of my first born while standing over our deer.   I want to experience these memories with my son/daughter and grandchildren someday.  We are often labeled but few non hunters actually understand.  It's not about shooting deer, it's about tradition and family.  Being part of nature and enjoying what God has given us.
As things have progressed with my education and WHU, I've come to realize a few things.  I have been told the DNR is lurking in the shadows on these forums.  Up until early this week, I second guessed that but I wrote a post, knowing it had incorrect information, trying to pull these individuals out and it worked. 
I've never been secretive of my name and contact information.  It doesn't take a rocket scientist(or wildlife biologist) to figure it out.   I have invited these individuals to discuss these matters but none have been courage enough to stand out from behind their "call" name.  I wonder why the DNR feels their time is better served lurking in these forum than to be educating the sportsmen of WI.  How do you stop an adversarial relationship with actions like that?
I am proud of the WI deer hunter.  We have come a long way.  I see hunters educating themselves, searching for answers and asking the right questions.  As you continue, my advise is to be the bigger person and remove your emotions.  Shake the warden's hand, ask if you can help or join an organization.  If you don't, outdoor journalists will continue label you as angry hunters and politicians/DNR will ignore you.  Don't let individuals try to confuse you with strange equations or a bunch of facts/figures.  Continue educating yourself, ask questions and contact your elected officials.  By doing all of this, you can help the all the organizations make change on your behalf.
As poor as the 2008 season was or how bad the outlook is for this season, this is an exciting time for the WI deer hunter.  Never have we been in a better position to be part of the deer management in Wisconsin.  We can do something that I don't believe has ever been done before.
I've come to the point were I must refrain from posting in forums.  Statements I make are reviewed and spun negatively against WHU and deer hunters.  Although I will miss the camradry of the members of this forum, I realize my time will be better served gathering information, educating and working for change in Wisconsin.
You all know where to find and contact me.  My tailgate always has room.

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RE: SAK method of population estimating

Postby Goose » Wed Feb 25, 2009 10:22 am

Well thats sad to hear, We'll miss your passion to be sure. As you know you'll always be welcome and I personally will miss your info. You have my email if you need anything or have anything interesting for me. Take care brother and good luck with your plans.

Genesis 27:3 Take your bow and quiver full of arrows out into the open country, and hunt some wild game.....

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RE: SAK method of population estimating

Postby bowhunter53 » Wed Feb 25, 2009 11:42 am

Sorry to see you go Fish

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RE: SAK method of population estimating

Postby buckhunter21 » Wed Feb 25, 2009 3:26 pm

I agree, that's sad to see you have to go Fish.  Thanks for all your great postings and info that you've supplied to us.  Feel free to step back in from time to time to say 'hey.'  Good luck with your endeavors and hope to talk to you soon!

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RE: SAK method of population estimating

Postby Wolf River Hunter » Thu Feb 26, 2009 5:19 am

Pretty new to the forums but I enjoyed reading what you had to say and appreciated the knowledge you would share. I also wanted to say "thanks" for taking the time and effort to help educate other WI hunters, information you provided was a valuable tool in helping readers such as myself understand some of the inner workings of our states agencies. Even tho you have "retired" I hope that you might still provide insight when it is needed, if not for yourself, but for the other hunters to use and understand. Thanks again.

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