Modeling the effects of opening the great dismal swamp to black bear hunting
1 / 16

- PowerPoint PPT Presentation

  • Uploaded on

Modeling the Effects of Opening the Great Dismal Swamp to Black Bear Hunting. Tristan Tronic. The Problem. Great Dismal Swamp National Wildlife Refuge is home to an estimated 300 black bears

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about '' - bachyen

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

The problem l.jpg
The Problem Black Bear Hunting

  • Great Dismal Swamp National Wildlife Refuge is home to an estimated 300 black bears

  • The Virginia Department of Game and Inland Fisheries opened the GDSNWR to a limited bear hunt December 1st and 2nd of 20 bears total

  • Several animal rights and environmental groups protested the VDGIF decision, saying the hunt would damage the fragile bear population

  • The VDGIF responded by saying the hunt would have a negligible impact

Modeling the effects of a limited hunt what s known l.jpg
Modeling the Effects of a Limited Hunt: Black Bear HuntingWhat’s Known

  • Bear population dynamics have been shown to depend only on the female population

  • Bears can be divided into four subgroups, each separated by about one year of development:

    Cubs, Nonreproductive subadults, Subadults, and Adults

Bear population model l.jpg
Bear Population Model Black Bear Hunting

Cn+1 = αSSn + αAAn

Nn+1 = βCCn

Sn+1 = βNNn

An+1 = βSSn + βAAn

α = reproduction rate

β = survival rate

Linear model for open season l.jpg

0 0 .28 .58 Black Bear Hunting

.8 0 0 0

0 .71 0 0

0 0 .76 .91





Linear Model for Open Season

  • Based on survivability and reproduction observed in hunted bears in western Virginia

Initial distribution of subpopulations not well known, except that half of the population will be female, and there will be about four times as many adults as subadults.

Results of linear model l.jpg
Results of Linear Model Black Bear Hunting

  • Population seems to grow despite hunting

  • But the linear model for an open season assumes a hunting pressure that is unrealistically low for Southeastern Virginia




Non linear model for fixed quota hunt l.jpg
Non-Linear Model for Fixed Quota Hunt Black Bear Hunting

Cn+1 = αSSn + αAAn

Nn+1 = βCCn

Sn+1 = βNNn

An+1 = βSSn + βAAn

Natural bear survival up to 25 – 30 years is very high, assumed to be 1 for this experiment

It is observed in Virginia that hunters kill female bears 40% of the time, and of those 60% are nonreproductive subadults, 10% are subadults, and 30% are adults

H = Number of bears allowed to be killed per year

βN = 1 – H*.4*.6/Nn

βS = 1 – H*.4*.1/Sn

βA = 1 – H*.4*.3/An - 1/25

Non linear model for fixed quota hunt8 l.jpg

1 Black Bear Hunting




Non-Linear Model for Fixed Quota Hunt

0 0 .28 .58

1 0 0 0

0 (1 – H*.24/Nn)0 0

0 0 (1 – H*.04/Sn) (1 – H*.12/An - .04)

Matlab program l.jpg
Matlab Program Black Bear Hunting

clear all






for n=1:19

A=[0 0 .28 .58; 1 0 0 0; 0 1-(h*.4*.6)/y(2,n) 0 0; 0 0 1-(h*.1*.4/y(3,n)) 1-1/25-(h*.3*.4)/y(4,n);]





legend('cubs','nonreproductive subadults','reproductive subadults', 'adults', 'total');

Results proposed 20 bears year l.jpg
Results: Black Bear HuntingProposed 20 bears/year

Results 100 bears year l.jpg
Results: Black Bear Hunting100 bears/year

Results 110 bears year l.jpg
Results: Black Bear Hunting110 bears/year

Results 20 bears year 25 of normal reproduction rate for adults and subadults l.jpg
Results: Black Bear Hunting20 bears/year, 25% of normal reproduction rate for adults and subadults

Problems with the model l.jpg
Problems with the Model Black Bear Hunting

  • Assumes that all bears born in refuge stay in refuge, and no new bears migrate in

  • Assumes perfect nonhunting survivability, not realistic for high human density area

  • Initial bear population uncertain

  • Assumes hunting patterns and bear reproduction will be the same as in western Virginia, which is geographically distinct

Conclusions l.jpg
Conclusions Black Bear Hunting

  • A limited hunt of 20 bears per year doesn’t seem to negatively affect the bear population

  • Given the uncertainty in the actual size and reproductive ability of the bear population, expanding the hunt further may cause extinction

Sources l.jpg
Sources Black Bear Hunting

“Bears on the Move.” Virginia Dept. of Game and Inland Fisheries. 2004.

“Great Dismal Swamp National Wildlife Refuge and Nansemond National Wildlife Refuge Final Comprehensive Conservation Plan July 2006”

Klenzendorf, Sybille. “Population Dynamics of Virginia’s hunted black bear population.”   Dissertation. Virginia Polytechnic Institute, 2002.

“Lottery will choose hunters for refuge's first bear hunt.” Applegate, Aaron.  Virginian- Pilot, October 7, 2006.