This was written by my son.
Bobcat Statistics- Wyatt John McNeill
In this paper, I will be citing the Bobcat Management Plan, which has/will be intact from 2007-2016. First I will go into a few basic things about this Plan, and why it is effective, and a good idea, and later I will go into detail as to why it is a bad idea.
In an effort to strengthen Bobcat populations in Utah the Bobcat Management Plan (BMP), was created. In a very basic sense it outlines trapping, hunting, and partaking of bobcats in Utah for various reasons, and in various ways. It however also states this:
a. Performance Targets
Variable Mean 95% Confidence Interval
Proportion of kittens and yearlings in the harvest 0.49 0.42 - 0.56
Adult Survival 0.68 0.65 - 0.72
% Females in the harvest 0.43 0.41 - 0.45
Set-days / bobcat 197 171 – 220
b. Strategies
i. Maintain or return to baseline management strategy of < 2 variables (net) are outside the historical range
1. Baseline strategy :
a. 6 tags / individual
b. Season from third Wednesday in November to the second Sunday in February
c. No cap on the number of tags sold
ii. Adjust the number of bobcat tags available to individuals (+ or – 1-2 tags) if any 2 (net) of the above performance targets are outside the historical range (outside the 95% CI) in the same direction.
iii. Adjust the length of the bobcat harvest season (+ or – 1-2 weeks) if any 3 (net) of the above performance targets are outside the historical range (outside the 95% CI) in the same direction. Implemented in addition to Strategy i.
iv. Cap the total number of bobcat tags available at 80% of the number of tags sold the previous year if all 4 of the above performance targets are outside the historical range (outside the 95% CI) in the direction indicating that harvest needs to be reduced. These tags would be sold on a first-come, first served basis. Implemented in addition to Strategies i and ii.
In a basic sense, it says that if any two of those confidence intervals are broken, the plan has the option to lower the tag limits + or -2 tags, reduce the number of tags sold, and also shorten the season by up to 2 weeks. In a general sense with good data, this would be a sound plan. However with corrupt data, or as Statisticians say “Data Bias”, this plan would have faults, as it does.
We will start from the beginning and look at the Proportion of Kittens and yearlings in the harvest. This is a number that would have very little bias, as most people will not fill this section out incorrectly. Leaving very little to no bias for this specific section. It effectively goes for Adult Survival, and % of females in the harvest. For these reasons I won’t focus completely on these but will touch down very quickly on why these numbers could be biased. With a lower amount of tags being used and available per person this creates a desire for large male bobcats, which although are more desired, are effectively what is hurting the populations in the long run.
When considering the data from previous years compared to the current year it is very nearly the same. Comparing 1990-1991, and 2004-2005 data, we can see very similar things. We can see the amount of Kittens/Adult Female is the same at .8, and the amount of Kittens per Adult is the same with .3. Now what is the main difference? The trap-days per bobcat. In 1990-1991 there was 145 trap nights per bobcat, and in 2004-2005, there were 236. (This is not even counting the 701 trap nights per bobcat in 2008-2009)
For the largest portion of Bias in data, is how questions are asked for the surveys for Bobcat Harvests. Beginning the surveyors ask a question such as, “How many traps did you have set out at one given time?, after which they ask, “How many days did you trap this year, would you say it was the whole year, that you had these traps out?” To explain this data, I will set up a mock scenario.
Lets say for example that a trapper has 100 traps (An average number for a somewhat serious trapper), and lets say he got asked these questions in this order. Being we had 69 days of trapping bobcats last year, 100 traps at 69 days, would be a total of 6,900 trap nights “set for bobcats”. Now lets say for instance he gets the allocated 3 bobcats. This would mean he effectively shows data for 2,300 trap nights per bobcat. And as the DNR said in their plan, if it goes over 220, automatically they have 1 chance to remove tags from trappers. Now however lets consider it if they asked this correctly, or if the trapper was informed what they are asking. Note the surveyors asked the question regarding all traps set that had a possibility for bobcats, not ones that are targeted for bobcats. Well, what constitutes a bobcat specific set? Generally one considers a “Walk Through” set a bobcat specific set, while other consider the Modern Day Dirt-hole Set to be a Coyote or Fox specific set. When considered this way, you have to look at different numbers. Lets say for 100 trap set, the person really has 10 traps which are considered bobcat set traps, and are used for walkthroughs. And lets say that realistically because of family he only trapped for 50 out of the 69 days. 50 days at 10 traps, gives you 500 set-days total, and with 3 bobcats you have a total set-days per bobcat of 166.6667.
When asking questions in such a way as to create bias, meaning to or not, in can create a means, which skews data. For example in the 2012-2013 season in Cache county a recorded “2” bobcats were taken; however trappers in Cache county recorded 42,298 trap days. Giving them a total of 21,149 trap nights per bobcat, in Cache county. This data, effectively called “outliers” is what boost the average trap-days per bobcat astronomically high, and which causes massive data bias.
Works Cited
"Furbearer Guide Book." Division Of Wildlife Resources. Division of Wildlife Resources, n.d. Web. 30 Sept. 2013.
"Bobcat Harvest Data." Division Of Wildlife Resources. Division of Wildlife Resources, n.d. Web. 30 Sept. 2013.
Basset, Stan, Jim Karpowitz, Ernie Millgate, and John Weiss. "Bobcat Management Plan." Division Of Wildlife Resources. Division of Wildlife Resources, n.d. Web. 30 Sept. 2013.
Thanks,
Moose
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