by Fish » Sun Feb 22, 2009 9:16 am
OK, gang....I'm going to explain a bit about "goal" and SAK. I'm trying to get a crash course in SAK so I can explain it at our WHU meetings. I'll start another post to explain SAK later and more info will soon be on WHU.
The Buck Recovery Rate is the percentage of bucks harvested out the total buck death. For instance, a 90% BRR means 90% of the bucks die from harvested and the remaining 10% die from other causes. The BRR is set by biologist but no data is available to base this on.
First, don't "poo,poo" SAK. SAK in it's pure form is one of the best models available. The problem is the constant changes to the model done by the DNR AND some variables which lack scientific data. Here is one major problem, the buck recovery rate. There is more to it but I'll give this formula and follow up in a later thread.
In 1990, unit 70A had a BRR of 90%, buck harvest of 1888 and an Ave Yearling Buck Percent of 86%. The annual mortality rate on an adult buck is calculated at BRR x AYBP or .90 x .86 = .77. Take this mortality rate of .77 and divide the buck harvest of that year (1888/.77 = 2452). 2452 was the preseason est of bucks. The total population is multipled by the amount of pre hunt bucks( the variable is called the Expansion Factor). For this unit the EP was 4.9. 2452 x 4.9 = 12015 deer in that unit.
Now just think about the BRR for now, don't cloud your head with the other stuff. Lets take a BRR of 80%. BBR x AYBP(.80 x .86 = .602). 1888/.602 = 3136 and then multiple this by the EF of 4.9. 3136 x 4.9 indicates a total population of 15,367 in this unit.
Back when the used a pure SAK model, the BRR wasn't used and/or it was a constant. Should some sort of BRR be used, maybe. For more information on the problem of BRR please review the SAK report on the DNR website.