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CWD Response Plan

Proposal

Prevention. Surveillance. Response.

Last Updated: 09/04/2019

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This document is intended to be a living document that will continue to be updated as input

from the public, external collaborators, and Pennsylvania Game Commission staff necessitate

changes to previous versions. Expect changes to occur frequently.

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Table of Contents

Title Page…………………………………………………………………………………………………………………………………..1

Living Document Disclaimer…………………………………………………………………….…………………………………2

Acknowledgements……………………………………………………………………………………………………………………4

Executive Summary……………………………………………………………………………………………………………………5

Introduction………………………………………………………………………………………………….……………………………5

Disease Overview………………………………………………………………………………….……………………….5

Human Health……………………………………………………………………………………………………….……….7

Impact to Deer Populations………………………………………………………………………………….……..…7

Agency Responsibility………………………………………………………………………………………….…………8

Captive Cervid Facilities…………………………………………………………………………………….….………..9

Stakeholder Responsibility…………………………………………….……………………….………….………..…9

Impacts to Hunting and Communities…………………………………………………………………….…….10

History of Chronic Wasting Disease in Pennsylvania………………………………………….…………10

Strategies in Other States and Countries……………………………………………………………..……….13

Lessons Learned in Pennsylvania………………………………………………………………………………….15

Management Goals and Objectives………………………………………………………………………………………….15

Management Actions……………………………………………………………………………………………………………….19

CWD Control Units and CWD-Established Areas……………………………………………………………19

Management Actions in CWD Established Areas ………………………….………………………………20

Management Actions in CWD Control Units…………………………………………………………………23

Elk Herd Considerations……………………………………………………………………………………………….26

Conclusion……………………………………………………………………………………………………………………………….27

Literature Cited………………………………………………………………………………………………………………………..28

Appendix 1: Distance Sampling to Estimate Deer Abundance………….………………………………………34

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Acknowledgments

We thank the many collaborators that contributed to this draft in a variety of capacities. Some

of these include: Dr. Krysten Schuler from Cornell University, Dr. Bryan Richards from USGS,

Nick Pinizzotto from the National Deer Alliance, Kip Adams from Quality Deer Management

Association, Dr. Michael Samuel now retired from University of Wisconsin-Madison, Dr.

Michelle Carstensen and Dr. Adam Landon from Minnesota Department of Natural Resources,

Dr. Tami Ryan from Wisconsin Department of Natural Resources, Dr. Kelly Straka from Michigan

Department of Natural Resources, Dr. Craig Miller from the University of Illinois, Dr. Lisa

Murphy and Dr. Julie Ellis from the University of Pennsylvania, Harris Glass and Kyle Van Why

from USDA-Wildlife Services, Dr. Kevin Brightbill and Dr. David Zellner from the Pennsylvania

Department of Agriculture, Emily Domoto, Ryan Reed and others from Pennsylvania

Department of Conservation and Natural Resources, Robb Miller-the Governor’s Advisor for

Hunting, Fishing, and Conservation, and many staff from the Pennsylvania Game Commission.

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Executive Summary

Since Chronic Wasting Disease (CWD) was first discovered in Colorado in 1967, it has continued

to spread throughout North America and into other continents. CWD is a serious threat to the

deer and elk in Pennsylvania. Despite preventative measures and extensive monitoring, CWD

has continually increased in prevalence and geographic spread in Pennsylvania since its

discovery in 2012. Data from other states suggests that with no change, Pennsylvania will reach

a CWD prevalence over 30% in the area where CWD was first detected in the next 10-20 years.

The Pennsylvania Game Commission, hunters, landowners and others have a responsibility to

protect deer and elk populations for current and future generations. More aggressive

management actions are needed to effectively manage CWD. Control Units will be created

around new, isolated cases where CWD can be managed most effectively. Management

changes may include increased antlerless permit allocation, additional antlered permits,

expanded hunting seasons, removal of antler point restrictions, mandatory sampling in Control

Units, and consideration of incentive programs. The main goals of CWD management in

Pennsylvania are: 1) Reduce risks of spreading CWD, 2) Monitor for spatial distribution and

prevalence of CWD, 2) monitor for spatial distribution and prevalence of CWD, 3) prevent the

establishment of CWD in new areas, and 4) maintain prevalence below 5% in CWD-Established

Areas and slow the geographic spread of CWD. In Control Units, the initial management step is

to reach a minimum sampling goal via hunting. If management objectives are not met in CWD

Control Units or Established Areas, the Pennsylvania Game Commission will seek to reach those

objectives through agency-directed targeted removals. Hunters and landowners will be allowed

more opportunity to actively participate in CWD management.

Introduction

Disease Overview

Chronic Wasting Disease (CWD) is an always fatal brain disease, currently affecting white-tailed

deer and is threatening elk in Pennsylvania. CWD has been identified in all North American

cervid species, which includes deer, elk, caribou and moose (Williams et al. 2002). CWD was

first detected in a captive deer facility in Colorado in 1967. It wasn’t until the 1980s that CWD

was detected in an adjacent free-ranging elk. As of 2018, CWD has been detected in 26 states in

the US, 4 Canadian provinces, South Korea, and Scandinavian countries (USGS 2019).

CWD belongs to a family of diseases known as transmissible spongiform encephalopathies

(TSE). Other TSEs include scrapie in sheep, bovine spongiform encephalopathy (mad cow

disease) in cattle, and Creutzfeldt-Jakob disease in humans. TSEs are believed to be caused by

prions or misfolded proteins. Prions are a “proteinaceous particle” consisting solely of protein,

with no nucleic acid genome (Prusiner 1998). While it is not known what causes normal prions

to misfold, normal prions can convert to an abnormal or distorted form. These abnormal prions

replicate by binding to and misfolding normal prion proteins, they accumulate in lymphoid and

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central nervous system tissues, eventually reaching the brain and causing clinical disease by

creating holes in the brain (Cohen 1999).

Figure 1. Distribution of Chronic Wasting Disease in North America as of 2019.

CWD transmission occurs through direct animal-to-animal contact or indirectly through prion

contaminated environments (Miller et al. 2004, Johnson et al. 2006). CWD-infected individuals

shed prions through saliva, urine, and feces (Mathiason et al. 2009). Despite research

conducted, there is currently no vaccine or treatment for CWD. Once in the environment, CWD

may remain infectious in the soil for several years (Miller et al. 2004). CWD prions can bind to

montmorillonite, a type of clay in soil, which may increase CWD infectivity (Johnson et al.

2006). Other laboratory research has shown that certain plants can absorb and uptake small

amounts of prions from contaminated soils, suggesting plants could also be a potential route of

infection (Rasmussen 2014, Pritzkow et al. 2015). While attempts to decontaminate infected

locations have been unsuccessful, a recent study found that humic acids extracted from soil

organic matter may decrease prion infectivity (Kuznetsova et al. 2018).

CWD, like other TSEs, is characterized by having long incubation periods before the animal

appears diseased. CWD-infected deer don’t show clinical signs of disease for up to 18 to 24

months (Tamgüney et al. 2009). Clinical symptoms of disease include lowered head, lowered

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ears, progressive weight loss, rough hair coat, excessive salivation, excessive thirst, excessive

urination, and behavioral changes (Williams 2005). These clinical signs are not unique to CWD

and could be due to many other conditions, such as malnutrition or vehicle trauma. CWD-

infected individuals are more likely to die from predators, vehicle collisions, or hunters before

CWD causes death because of the increased vulnerability (Krumm et al. 2005, Edmunds et al.

2016, DeVivo et al. 2017).

Genetics plays a role in CWD susceptibility. Variations in the prion protein (PRNP) gene can

affect individual susceptibility to and progression of CWD (Robinson et al. 2012). Although

there is no genetic immunity, some rare genotypes are associated with lower rates of CWD

infection and slower progression of clinical disease (Hamir et al. 2006). However, the individuals

with the less susceptible genotype are not immune to CWD. Certain populations of deer in

Pennsylvania (Bedford, Blair, Huntingdon, Franklin, and Fulton) have a significantly higher

frequency of the more susceptible genotype than deer populations previously surveyed from

New Jersey, Wisconsin, Wyoming, and Canada (Blanchong et al. 2009, Robinson et al. 2012,

Miller and Walter 2019). Therefore, if not managed effectively, CWD might have a greater

impact on the deer population in portions of Pennsylvania compared to other regions.

Human Health

To date, there have been no known cases of CWD infecting humans. However, the Centers for

Disease Control and Prevention recommends no one consume CWD-infected meat (CDC, 2019).

Researchers continue to investigate the susceptibility of human infection to CWD, but no link

has been found to date. Experimental infections demonstrated that primates (squirrel

monkeys) could acquire CWD through oral consumption of infected meat or brain tissue (Race

et al. 2014, Waddell et al. 2018). Consequently, people should avoid exposure to CWD through

handling or consuming of infected animals. Hunters are advised to use gloves whenever

handling a deer carcass. Within Disease Management Areas (DMAs), hunters can receive free

CWD test results by submitting their deer head into a head collection bin. Locations of head

collection bins can be found on the Pennsylvania Game Commission website: www.pgc.pa.gov

Impacts to Deer Populations

CWD can have population-level impacts in areas of high prevalence. In Wyoming, where CWD

was first detected in 1985, there was a 10% annual decline in white-tailed deer populations in

an area with high CWD prevalence (Figure 2). CWD-infected white-tailed deer were 4.5 times

more likely to die annually than uninfected deer (Edmunds et al. 2016). Mule deer research also

showed annual population declines greater than 20% in an area with a high CWD prevalence

(DeVivo et al. 2017). In Colorado, the estimated mule deer population declined in a study area

of high CWD prevalence (>25 %). In the same area, estimated average life expectancy for

infected deer was an additional 1.6 years, compared to an additional 5.2 years for uninfected

deer (Miller et al. 2008). In some areas of Wisconsin, more than 55% of adult males and 35% of

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adult females were infected with CWD; 75% of these infected deer died in the first year of study

(Wisconsin Department of Natural Resources 2019).

Figure 2. In the absence of disease management in Hunt Unit 65 in Southeastern Wyoming, the

CWD prevalence has increased since 2001, while CWD has contributed the decline of mule deer

(DeVivo et al. 2017) and white-tailed deer (not shown; Edmunds et al. 2016) over the same time

span. Source: Wyoming Game and Fish Department – Big Game Reports

Agency Responsibility

The Pennsylvania Game Commission is responsible for managing Pennsylvania’s free-ranging

mammals and birds for current and future generations. It would be irresponsible for the

Pennsylvania Game Commission not to take the threat of CWD seriously. The alternative option

of taking no further actions to combat CWD would also be irresponsible, given the current

knowledge of the disease and how it has impacted cervid populations in other states. State

wildlife agencies should manage for managing healthy, sustainable, free-ranging cervid

populations. The Pennsylvania Game Commission will continue to utilize the best available

science to make conscientious management decisions about CWD. It is imperative that the

Pennsylvania Game Commission take measures to prevent the disease from increasing in

prevalence and from spreading to other parts of the state. Doing this will ease CWD

management in the future if new, more acceptable and effective management strategies are

developed.

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Captive Cervid Facilities

Since 2012, 16 captive cervid facilities (i.e. deer farms) have tested positive for CWD in

Pennsylvania. Eight captive herds that tested positive continue to have live animals on the

premise. All these facilities owned/own white-tailed deer. While the Pennsylvania Game

Commission has no regulatory authority over captive cervid facilities, the Pennsylvania Game

Commission will continue to work with the Pennsylvania Department of Agriculture (PDA; who

regulates the captive cervid industry) to create solutions that protect the deer and elk of

Pennsylvania. Some of those solutions include preventing contact between free-ranging and

captive deer (i.e. double fencing), prevent movement of captive cervids in high-risk CWD areas

(e.g. DMA 2) to areas outside DMAs to prevent introduction of CWD into previously uninfected

areas, mandatory CWD testing of all deer that die in captive cervid facilities, and mandatory

CWD sampling of a minimum number of animals tested per year in each captive cervid facility.

Stakeholder Responsibility

Hunters, Landowners, and other stakeholders occupy a critical role in CWD management.

Without their support and participation, we cannot be successful at managing this disease. The

Pennsylvania Game Commission will continue to engage hunters, landowners, other

governmental agencies, universities, and non-governmental organizations in the development

and implementation of a CWD response plan.

For over 100 years, hunters have been at the forefront of wildlife conservation success stories.

In the 1800s, hunters and anglers realized that to conserve rapidly disappearing wildlife they

would have to set limits and take responsibility for future management. Managing CWD in

Pennsylvania will be no different. Experiences from other states have shown when state wildlife

agencies and hunters do not work together, CWD is not successfully managed (Uehlinger et al.

2016). All stakeholders must stay informed, involved, and assist in managing CWD.

Particularly, hunters have an obligation to understand and abide by all current regulations and

best practices regarding CWD. For example, it is unlawful to transport high-risk parts outside of

DMAs.

High-risk cervid parts include the head (more specifically the brain, tonsils, eyes, and

retropharyngeal lymph nodes); spinal cord/backbone; spleen; skull plate with attached antlers,

if visible brain or spinal cord matter is present; upper canine teeth, if root structure or other

soft material is present; any object or article containing visible brain or spinal cord material;

unfinished taxidermy mounts; or brain-tanned hides.

Once the high-risk parts are removed, the following items can be brought into Pennsylvania, or

exported from a DMA: the remaining meat, on or off the bone; skull plate with antlers

attached, if no brain or spinal cord material is present; cleaned capes with no visible brain or

spinal cord material present; tanned or raw hide with no visible brain or spinal cord material

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present; upper canine teeth, if no root structure or soft material is present; and finished

taxidermy mounts.

Movement of infected cervid carcasses, especially high-risk parts, is 1 of the known risks for

introducing CWD prions to new areas. Once infected, prions primarily accumulate in the central

nervous system (Kretzschmar et al. 1986), however prions have been detected in blood, saliva,

urine, and feces (Angers et al. 2006, Kramm et al. 2017). Since prions accumulate in the central

nervous system, the parts listed above are considered high-risk for transmitting disease.

It is best to dispose of high-risk parts in the commercial trash or a high-risk parts dumpster

provided by the Pennsylvania Game Commission. Within DMAs, it is unlawful to feed deer or

use urine-based lures. Not abiding by these regulations can increase the spread and severity of

the disease. Hunters can also take advantage of the increased role that the Pennsylvania Game

Commission wants hunters to play in CWD management. In part, this includes increased

hunting opportunity in critical areas, submitting samples for free CWD testing, and working

with the Pennsylvania Game Commission to develop solutions.

Landowners can also help by staying up to date with current information, educating others with

correct information, and allowing access for hunting or targeted removals on property.

For more information on what you can do to help control CWD, visit the Pennsylvania Game

Commission website: https://www.pgc.pa.gov

Impacts to Hunting and Communities

Declines in deer or elk populations can cause reduced hunter opportunity (DeVivo et al. 2017).

Even before populations decline from CWD, hunters may choose to hunt elsewhere or stop

hunting altogether. The first year after CWD was discovered in Wisconsin, hunting license sales

dropped 10% (Wisconsin Department of Natural Resources 2016). Other wildlife conservation

programs dependent on license sales, suffered as a result (Vaske et al. 2004). Over 1 in 5

hunters in Pennsylvania said their interest in deer hunting would be reduced if any deer were

detected with CWD in the area they hunt (Pennsylvania Game Commission, unpublished data,

2017). The potential economic losses of a decline in hunting participation in Pennsylvania would

have significant negative impacts on funding for conservation of all wildlife. In addition, CWD

could negatively affect the social and economic stability of communities that depend on

hunting for revenue.

History of Chronic Wasting Disease in Pennsylvania

The Pennsylvania Game Commission began monitoring for CWD in 2002, 10 years before it was

detected in Pennsylvania. As of 2019, nearly 80,000 deer and over 800 elk have been tested for

CWD in Pennsylvania. Surveillance efforts include testing road-killed deer, hunter-harvested

deer and elk, escaped captive deer or elk, and deer/elk showing clinical signs of CWD.

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CWD was first detected in Pennsylvania in October 2012 in a captive white-tailed deer facility in

Adams County. Shortly after, CWD was detected in 3 free-ranging white-tailed deer in Bedford

and Blair county. Since, CWD prevalence has increased and CWD has spread geographically. As

of May 2019, a total of 250 free-ranging deer have tested positive for CWD in Pennsylvania

(Figure 3). Two hundred forty-six of these positives were detected in Disease Management Area

2, with the remaining 4 positives detected in Disease Management Area 3. Not only has the

number of deer detected continually increased over the years, the percentage of deer that test

positive for CWD (i.e. prevalence) has also continually increased (Figure 4).

When new CWD detections are found in free-ranging or captive deer in Pennsylvania, a 10-mile radius is created around that detection to either expand or establish a Disease Management Area. If a new CWD positive is detected near a DMA’s boundary or outside of an existing DMA, the existing DMA could expand into a larger area or a new DMA may be created. A 10-mile buffer around positive CWD detections is used because that encompasses the dispersal distances of the majority of deer in Pennsylvania (Long et al. 2008; Lutz et al. 2015). Enhanced CWD monitoring and specific regulations exist within DMAs to help slow the spread of CWD.

Figure 3. Number of positive free-ranging deer detected in Pennsylvania by year from statewide

CWD testing.

3 2 512

25

79

123

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40

60

80

100

120

140

2012 2013 2014 2015 2016 2017 2018

No

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Figure 4. Prevalence (% of all samples that test positive) by year from all samples taken in Blair,

Bedford, and Fulton Counties, Pennsylvania. Note: the large drop in prevalence from 2012 to

2013 likely stems from “sampling error” because of a low sample size in 2012, not a true drop in

prevalence. Samples sizes from 2012-2018 were 142, 1006, 780, 1253, 1257, 2346, and 2382

samples, respectively.

DMA 1 was established in 2012 in Adams County after a captive cervid facility (i.e. deer farm) tested positive for CWD. All deer were depopulated from the farm and DMA1 was dissolved in 2017 after no additional deer were detected with CWD for 5 consecutive years. DMA 2 was established in 2012 after the detection of 3 free-ranging deer tested positive in Blair and Bedford County. DMA 2 originally covered 892 square miles in Blair and Bedford counties. Due to the discovery of new CWD cases every year, DMA 2 in 2019 now covers 6,715 square miles in portions of 17 counties in south-central Pennsylvania. Eleven captive cervid facilities have tested positive for CWD within DMA 2. Three farms have depopulated while the remaining 7 have live deer on the premises. DMA 3 was established in 2014 after CWD was detected in 2 captive cervid facilities in Jefferson county. Those farms were depopulated of all animals. In 2017, Disease Management Area 3 expanded to cover over 2,000 square miles due to the detection of CWD in 3 free-ranging white-tailed deer in Clearfield and Jefferson county. DMA 3 was expanded further in 2019 because a deer within a captive cervid facility in Clearfield County tested positive after being transported from a captive cervid facility in DMA 2 (Fulton County). Another free-ranging deer (from a vehicle collision) tested positive in Jefferson County in 2019.

0

1

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2012 2013 2014 2015 2016 2017 2018

Pre

vale

nce

%

Year

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DMA 4 was established in 2018 after CWD was detected in a captive cervid facility in Lancaster county. The farm was depopulated of all deer. Disease Management Area 4 covers 346 square miles in Lancaster, Lebanon, and Berks counties. To date, no additional CWD detections have been found in Disease Management Area 4.

Figure 5. Current Disease Management Areas (DMAs; blue polygons) in Pennsylvania. (Note: DMA 1 that surrounded the captive cervid facility in Adams County was dissolved after 5 years of no additional positive detections)

Strategies in Other States and Countries

Options to manage CWD where it has become established are currently limited, however where success has occurred, states used a combination of increased hunter harvest and targeted removals (i.e. agency-directed culling) to reduce CWD prevalence. For example, Illinois first detected CWD in 2002 and actively began targeted removals of deer the following year. Targeted removals in Illinois remove CWD-infected deer at 2.5 times the rate that hunters do in the infected areas because targeted removals focus on removing deer near known CWD detections (Dufford and McDonald 2018). Through consistent management actions for over 15 years, prevalence in the area it was originally detected is currently 3.3% (Dufford and McDonald 2018). In contrast, Wisconsin also detected CWD in 2002 and began targeted removals of deer in 2003. Due to public pushback against Wisconsin Department of Natural Resources, Wisconsin ceased targeted removals in 2007 (Uehlinger et al. 2016). Since that time, CWD has spread geographically and increased in prevalence, with some areas showing over 55% of adult bucks

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infected (Wisconsin Department of Natural Resources 2019). West Virginia has undertaken similar management actions to that of Pennsylvania and continues to see prevalence increase in their disease zones (Figure 6).

Figure 6. CWD Prevalence trajectory since detection for West Virginia, Wisconsin, and Pennsylvania (Pennsylvania Game Commission, unpublished data, 2018; West Virginia, unpublished data, 2018; Wisconsin DNR 2019). Several examples exist where CWD was detected in free-ranging deer and did not become established in the local deer population after aggressive management actions were taken. In 2005, New York detected CWD in a captive deer facility in Oneida county. Within weeks, deer managers used a combination of hunter harvest and targeted removals to remove over 300 deer in the local area. Two additional free-ranging deer were detected during their initial response. New York has not detected additional CWD positives since their initial response in 2005 (New York State Department of Environmental Conservation, 2019). Similarly, Minnesota detected CWD in a free-ranging deer in Olmsted County in 2010, which was only 2 miles from a CWD-positive captive deer facility. Minnesota implemented immediate management actions within the local area via a combination of additional hunter harvest and agency-sponsored targeted removals. This effort resulted in over 4,000 deer samples over 3 years. No additional CWD positives were found in the local free-ranging deer population (Minnesota DNR, 2019). These success stories from other states provide hope that increased hunter harvest and targeted removals, if conducted quickly and effectively after CWD is detected in a new area, can be used to successfully combat CWD. To date, reducing local deer populations is the only

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management strategy that has shown any success at stabilizing or reducing prevalence of CWD (Manjerovic et al. 2014). Reducing deer populations surrounding new CWD detections lowers disease transmission through reduced contact among deer (Tosa et al. 2017). In addition, reducing deer numbers around new CWD detections, reduces the number of deer shedding prions into the environment. Norway has taken the most aggressive steps to eliminate CWD by removing an entire reindeer herd, over 2,400 animals, in an area where CWD had been detected. They plan to leave this area devoid of animals for 5 years to try to eliminate the disease (the Pennsylvania Game Commission will not attempt to eradicate deer or elk in any areas). Lessons Learned in Pennsylvania

After more than 6 years of managing CWD in Pennsylvania, it is clear that controlling CWD in Pennsylvania’s free-ranging white-tailed deer is extremely challenging. Managing CWD requires substantial commitment of human and financial resources from the Pennsylvania Game Commission over an extended period of time. If the trajectory of disease increases in Pennsylvania as it has in other states, with no change in management actions, prevalence in the Established Area (portions of Blair, Bedford, and Fulton county) will likely exceed 30% in the next 10-20 years. Without a change in management, CWD will continue to increase and spread. Although the public generally does not want to see the disease increase, reducing deer populations to manage CWD is controversial. However, alternative options for managing CWD in free-ranging deer are limited. Communication efforts will be critical to increase the public’s understanding of, support for, and participation in CWD management. The Pennsylvania Game Commission is committed to increasing stakeholder engagement and outreach to local communities, hunters, and landowners affected by CWD. In addition to management of CWD, the Pennsylvania Game Commission will conduct human dimensions studies to inform future management decisions.

Management Goals and Objectives

Goal 1: Reduce Risks of Spreading CWD

Objective 1: Contain disease and stop introduction of prions via movement of high-risk

cervid parts.

When there is a new CWD detection in either a captive or free-ranging cervid, a 10-mile

radius DMA is established. If a new CWD positive is detected within 10-miles of a

current DMA boundary, the existing DMA may expand into a larger DMA. With DMAs,

specific rules apply to help prevent the spread of CWD into uninfected areas.

Within the state, it is unlawful to remove or export high-risk cervid parts from a DMA. In

addition, it is also unlawful to import high-risk cervid parts from CWD-positive states. As

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of May 2019, the importation of high-risk cervid parts are prohibited from 26 states and

3 Canadian provinces.

Objective 2: Reduce the risks of transmission between captive and free-ranging deer or

elk.

Work collaboratively with the Pennsylvania Department of Agriculture and the captive

cervid industry to minimize the risks to both free-ranging and captive cervids. Some of

the solutions include preventing contact between free-ranging and captive deer,

prevent movement of captive cervids in high risk CWD areas (DMAs) to areas outside

DMAs to prevent introduction of CWD into previously uninfected areas, mandatory

CWD testing of all deer that die in captive cervid facilities, and mandatory CWD

sampling of a minimum number of animals tested per year in each captive cervid facility.

Objective 3: Limit human-related activities that unnaturally congregate free-ranging

cervids.

Within DMAs, it is illegal to feed free-ranging cervids. Research suggests that CWD is

transmitted by direct contact between infected and uninfected individuals and indirectly

through prion contaminated environments. Prions can be shed onto the environment

through saliva, urine, feces (Mathiason et al. 2009), or through infected carcasses (Miller

et al. 2004). Once in the environment, prions can remain infectious for several years

(Johnson et al. 2006).

Feeding can negatively affect disease transmission by increasing contact rates and

promoting pathogen accumulation around feeding sites (Murray et al. 2016). Feeding,

including the use of mineral licks, causes deer and elk to congregate in ways they would

not do so naturally. In addition, deer and elk urinate and defecate in these same areas.

If 1 infected deer is in the area, increasing contact between individuals and increasing

environmental contamination only increases the risk of spreading CWD. For this reason,

feeding—including the use of mineral licks—is illegal in Pennsylvania’s DMAs.

Within DMAs, the use and possession of natural urine-based attractants is also

prohibited. As stated above, prions can be shed through saliva, urine, and feces

(Mathiason et al. 2009, Gough et al. 2010). While the amount of prions required to

cause clinical or subclinical infection of CWD is currently unknown, the use of natural

urine-based attractants still poses a potential risk of transmitting CWD. The

Pennsylvania Game Commission prohibits the use of urine-based attractants within

DMAs for the purpose of avoiding the unnatural congregation of deer or elk to a specific

area.

Goal 2: Monitor for Spatial Distribution and Prevalence of CWD

Objective 4: Continue state-wide surveillance efforts to enhance likelihood of detecting

new introductions of CWD.

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Early detection of CWD is critical to implement management strategies that are aimed

at preventing the establishment of CWD in new areas. The Pennsylvania Game

Commission will continue statewide surveillance efforts for CWD. State-wide

surveillance efforts in Pennsylvania includes random sampling of hunter-harvested deer,

immediate removal and testing of escaped captive cervids, and collection and testing of

any free-ranging deer or elk behaving abnormally or displaying clinical signs of CWD.

Hunter-harvested deer are randomly sampled from cooperating meat processors and

across the state. Random surveillance of free-ranging white-tailed deer has a low

probability of detecting CWD at low (<1%) prevalence but can contribute to CWD

detection and monitoring (Pennsylvania Game Commission, unpublished data 2012).

Given limitations of active surveillance as a CWD detection program, free-ranging

surveillance is designed to: 1) train and test sample collection, extraction, and testing

procedures and personnel, 2) annually sample and test 4,000 hunter-killed deer 3)

provide scientific baseline data on presence and distribution of CWD in Pennsylvania, 4)

increase public awareness concerning CWD surveillance activities, and 5) potentially

provide a platform for additional disease monitoring.

Our active surveillance sampling design for deer is based on Wildlife Management Units

(WMUs). Quotas are created for each WMU based on the proportion of the state’s deer

population occurring in that WMU. Based on simulation modeling (Diefenbach et al.

2004), we expect a sample of 4,000 will provide a 62% chance of detecting CWD if

prevalence is 1% in any WMU. This sample size represents the maximum number that

can be collected by our personnel and infrastructure. Ongoing surveillance strengthens

our abilities for future CWD events.

All successful elk hunters are required to present their harvest at a designated check

station. At the check station, trained Pennsylvania Game Commission staff extract tissue

samples (i.e. obex and retropharyngeal lymph nodes) for testing from all harvests,

unless the hunter intends to have their harvest mounted. If the hunter intends to get

their harvest mounted, instructions and materials including postage-paid shipping

containers for transport of the caped head to the laboratory are provided to the hunter.

The objective for hunter-harvested elk is to collect samples from all harvested elk over 1

year of age.

All hunter-harvested elk are tested for CWD. As of May 2019, the Pennsylvania Game

Commission has tested 809 free-ranging elk for CWD and to date CWD has not been

detected in Pennsylvania’s free-ranging elk. Samples from hunter-harvested white-tailed

deer are collected in one of two ways: through the voluntary submission of hunter-

harvested deer heads in head collection bins provided by the Pennsylvania Game

Commission or through a random collection of hunter-harvested heads taken from meat

processors throughout the state.

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Objective 5: Continue surveillance efforts within Disease Management Areas to estimate

prevalence.

In addition to state-wide surveillance efforts noted above, increased surveillance occurs

within DMAs through sampling voluntary submissions of hunter-harvest deer, and

sampling road-killed deer. Additional samples within DMAs are used to estimate CWD

prevalence and spatial distribution.

The Pennsylvania Game Commission provides head collection bins for voluntary

submissions of hunter-harvested deer within DMAs. To encourage hunters to help

surveillance efforts, the Pennsylvania Game Commission tests each submitted head at

no cost to the hunter. Hunters are instructed to keep the harvest tag attached to the ear

for identification purposes and to double-bag all submitted heads to prevent

contamination from other submissions. All samples from head collection bins are sent

to the Pennsylvania Veterinary Laboratory in Harrisburg for CWD testing through

enzyme-linked immunosorbent assay (ELISA) or immunochemistry (IHC). All samples

that test positive are then tested again for confirmation via another IHC test.

Contractors are employed within DMAs, to collect road-killed deer from state and local

roads. Contractors are instructed to deliver carcasses to designated deer processing

locations, where trained Pennsylvania Game Commission staff extract samples (i.e. obex

and retropharyngeal lymph nodes) for testing. Remaining carcass parts are discarded

into dumpsters within these areas and disposed of in approved landfills to prevent

environmental contamination.

Currently the only federally approved CWD tests for cervids are IHC, ELISA, and Western

blot. As a general practice, all suspect positive ELISA and Western blot tests should be

confirmed with IHC (USDA 2013). The obex and retropharyngeal lymph nodes are the

preferred tissue samples for testing because data suggests these may be early CWD

detection sites (Miller and Williams 2002, Spraker et al. 2004). Since all federally

approved CWD tests require the removal of the obex and retropharyngeal lymph nodes,

all tests are done postmortem (i.e. after death). There are no tests that can be done in

the field because ELISA and IHC are both analyzed in the lab and require several steps

over the course of days and sterile environments to reduce the likelihood of false

positive results.

Goal 3: Prevent the Establishment of CWD in New Areas, Once Detected

Objective 6: Reduce potential for disease transmission and limit environmental

contamination of prions by quickly and effectively reducing local free-ranging cervid

populations around new CWD detections.

Goal 4: Maintain Prevalence below 5% in Established Areas and Slow the Geographic Spread

of CWD

19

Objective 7: Reduce free-ranging cervid populations within areas where CWD is

established and at highest infections rates.

CWD prevalence should remain below 5% in the established area. Prevalence will be

calculated from hunter-harvested deer only. However, it could take several years for

management actions to lower CWD prevalence. Lowering deer densities in small areas

with the highest prevalence might reduce natural movements of infected cervids to

uninfected areas of the state (long et al. 2008, lutz et al. 2015).

Management Actions

CWD Control Units and CWD-Established Areas CWD-Established Areas are characterized by a contiguous area where CWD positive cases are within 10 miles of one another and where CWD prevalence has remained >1% for at least 2 consecutive years (Figure 7). Currently, there would only be 1 established area in Pennsylvania, which would be centered in Blair, Bedford and Fulton counties. The Established Area boundaries will be delineated by easily identifiable boundaries such as roads or rivers. A CWD Control Unit is created when a new, isolated CWD positive case is detected in free-ranging or captive cervid greater than 10 miles from another positive detection. A 3-mile radius buffer is drawn around the new, isolated detection. This 3-mile buffer is the foundation to create a CWD Control Unit. The CWD Control Unit boundaries are then delineated to follow easily identifiable boundaries such as roads or rivers. Therefore, the buffer may sometimes fall outside or slightly inside of the 3-mile radius buffer. CWD Control Units are areas within DMAs where the status of the disease is yet uncertain; CWD may or may not be established in the environment (e.g. in the soil). For this reason, they are of particular concern for quick management action. CWD infections exhibit a clustered distribution, with highest prevalence occurring near the point of introduction (Osnas et al. 2009). This suggests that deer or elk in closer proximity to CWD detections are more likely to become infected with CWD (Joly et al. 2006). Therefore, areas directly surrounding CWD detections are considered high risk for transmission and increased management is needed to control the disease. Within Control Units, the main objective is to remove CWD positive deer quickly before CWD becomes established in the local deer population and/or environment (e.g. soil). Once established in the environment, there is no known way to eradicate CWD. CWD Control Units will not be created in areas where CWD is established in the environment. In Established Areas, the objective is to maintain the CWD prevalence below 5%.

20

Figure 7. Map of the CWD-Established Area (within bold black line) and examples of CWD Control Units (oranges circles) around new, isolated cases. Management Actions in CWD-Established Areas Since detection in Blair and Bedford counties in 2012, CWD prevalence has continued to increase until today and has spread outward every year. In this area, CWD may have become established in the environment and with current science it is unrealistic to eradicate the disease. However, it is possible to stop the increase or reduce prevalence in this area (Dufford and McDonald 2018). That is the main management objective for this area; to lower prevalence, with the goal of slowing the spread of CWD. To date, increasing hunter harvest and conducting targeted removals is the only management strategy that has shown any success in stabilizing CWD prevalence (Manjerovic et al. 2014, Dufford and McDonald 2018). Increased hunting opportunities and reduced restrictions will be offered to hunters within CWD-Established Areas. Increased ease and flexibility will give hunters the first opportunity to harvest more deer and collect more CWD samples. Management actions within CWD-Established Areas will include: 1. Maximize hunting opportunities: Changes within CWD Control Units may include:

a) Expanded hunting seasons:

21

*Early Firearm Season: This season combines what was previously the dates for the muzzleloader and special firearms season. Antlered and antlerless deer may be harvested with all arms and ammunitions during this season.

**Regular Firearm Season: All license holders may harvest antlerless deer throughout this season; concurrent antlered and antlerless seasons like is currently implemented in WMUs 2B, 5C, 5D.

***Extended Firearm Season: Antlerless only (except with the use of flintlock during flintlock season), as currently implemented in Allegheny, Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties.

b) Removal of antler point restrictions within DMAs: In Pennsylvania, adults bucks are nearly 3 times more likely to be infected with CWD than all other deer (Table 1). Removing antler point restrictions will allow hunters to harvest more bucks. Preliminary modeling by USGS-PA Cooperative Research Unit demonstrated that removal of antler point restrictions would reduce the number of deer infected with CWD by 20%. Removing antler point restrictions and increasing antlerless harvest would reduce the number of deer infected with CWD by 40% or more (D.R. Diefenbach, U.S. Geological Survey, personal communication). Table 1. Infection for fawns, yearlings, and adults from 2016-2018 in Blair, Bedford, and

Fulton counties of Disease Management Area 2.

Fawn Yearling ADULT

Both sexes Female Male Female Male

2016 NA 0.9 1.0 1.2 3.8

2017 1.9 2.2 1.5 1.3 5.2

2018 1.8 1.7 2.4 2.9 6.6

Average 1.9 1.7 1.8 2.0 5.5

c) Increased allocation of antlerless harvest tags: Hunters can harvest antlerless deer using

DMAP permits during any portion of the hunting season. Currently, DMAP units administered by Pennsylvania Game Commission within DMAs allocate 1 permit per 50 acres or 1 permit per 25 acres, depending on the unit. This allocation can be increased in the future to allow more hunters the opportunity to harvest antlerless deer and to meet management objectives.

Dates Arms & Ammunition

License Holders Eligible

Oct. 17-26, 2020* All methods All

Nov. 28 - Dec. 12, 2020** All methods All

Dec. 26, 2020 – Jan. 30, 2021*** All methods All

22

2. Consider incentive programs: Incentive programs could be an effective tool to increase land access for hunters and allow additional deer to be taken in areas where it is most needed to control CWD. During 2019-2020, Pennsylvania Game Commission will survey hunters and landowners to determine if there are incentive programs that would be effective and supported.

3.Targeted removals (as needed): The Pennsylvania Game Commission wants hunters to have

the first opportunity to meet management objectives through increased deer harvest. We also want hunters to be part of the solution and be successful at managing CWD. Nearly all results from CWD samples collected during hunting seasons should be analyzed by Feb 1. If prevalence is not maintained below 5% in the CWD-Established Area, Pennsylvania Game Commission will strive to reach that objective through agency-directed targeted removals. It may take more than 1 year of management actions to reach the objective of reducing and stabilizing CWD prevalence below 5%. Targeted removals are small-scale operations, that would remove deer from small areas with the highest concentration of positive detections (Figure 8). Targeted removals reduce the number of infected deer on the landscape, the number of potential dispersers that can spread CWD to new areas (Long et al. 2008, Lutz et al. 2015), and can lead to stable or reduced levels of infection (Manjerovic et al. 2014, Dufford and McDonald 2018).

Figure 8. Map showing where CWD positive deer were detected at highest concentrations (yellow) in Pennsylvania. The actual number of deer remaining on the landscape to achieve

23

disease management objectives may vary by location. The objective is not to remove all deer from the area. The main objective is to lower CWD prevalence and slow the spread of CWD. Reducing local deer numbers is the mechanism to achieve the main objectives, not the objective itself. If the CWD prevalence is declining or remains low (<5%), then deer density, regardless of the number – is acceptable for disease management purposes. Management Actions in CWD Control Units Increased hunting opportunities and reduced restrictions will be offered to hunters within Control Units. Increased ease and flexibility will give hunters the first opportunity to harvest more deer and collect more CWD samples to meet management objectives. 1. Deer Density Survey: Before hunting seasons begin, surveys will be conducted within each

Control Unit to estimate deer density. The surveys will be conducted by Pennsylvania Game Commission staff via a road-based, Distance Sampling method (Appendix 1).

2. Sample Collection via Hunter Harvest: The estimated deer density will determine the

minimum sample quota that we will need to test to be 99% confident we would detect CWD if at a 1% prevalence. Each Control Unit will have a minimum sample size quota of 350 deer. If deer densities are significantly higher than 30 deer per square mile, then a minimum sample size will need to be larger than 350 deer to be 99% confident that we can detect CWD at a 1% prevalence (given certain assumptions, Belsare et al. 2018). The minimum sample size will be slightly different for each Control Unit, based on the population estimate of deer. Across Pennsylvania, hunters harvest an average of 8 deer/mi2. To reach the minimum sample size quota needed in an average Control Unit, hunters would have to harvest approximately 4 deer/mi2 more than normal and submit all heads for testing. Head collection bins will be available in each Control Unit. If no additional detections of CWD occur after 3 years of reaching the minimum sampling quota, the Control Unit would be dissolved.

a.) Mandatory sampling in Control Units: Hunters must submit samples of all deer

harvested in a Control Unit within 72 hours of harvest. Hunters should submit heads to Pennsylvania Game Commission for testing via head collection bins that will be placed within each Control Unit. Hunters are responsible for filling out and securing a tag to the ear of the deer, removing the head, bagging the head, and placing it in a collection bin for testing. Antlers should be removed before submitting the head into a head collection bin. If hunters harvest a buck that they want to mount they may have the cape and skull cap with antlers removed before submitting the head for sampling.

3. Landowner Interaction: All landowners that own more than 5 acres within a Control Unit will

receive written communication before September each year with detailed information

including: a) CWD has been detected nearby, b) requirements associated with hunting in a

Control Unit, c) Control Unit boundaries, d) instructions on how to obtain more deer tags, if

24

desired, d) locations of head collection bins, e) an invitation to attend a local public meeting

to discuss the upcoming hunting season, sample size quota, and management changes, and

f) other pertinent information.

4. Maximize hunting opportunities: Changes within CWD Control Units may include:

d) Expanded hunting seasons: i. Option 1- Same season dates that are in effect in Special Regulation Areas

ii. Option 2 – Same season dates as proposed in the CWD-Established Areas:

*Early Firearm Season: This season combines what was previously the dates for the muzzleloader and special firearms season. Antlered and antlerless deer may be harvested with all arms and ammunitions during this season.

**Regular Firearm Season: All license holders may harvest antlerless deer throughout this season; concurrent antlered and antlerless seasons like is currently implemented in WMUs 2B, 5C, 5D.

***Extended Firearm Season: Antlerless only (except with the use of flintlock during flintlock season), as currently implemented in Allegheny, Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties.

e) Removal of antler point restrictions within DMA: In Pennsylvania, adults bucks are

nearly 3 times more likely to be infected with CWD than all other deer (Table 1). Removing antler point restrictions will allow hunters to harvest more bucks. Preliminary modeling by USGS-PA Cooperative Research Unit demonstrated that removal of antler point restrictions would reduce the number of infected deer by 20%. Removing antler point restrictions and increasing antlerless harvest would reduce the number of infected deer by 40% or more (D.R. Diefenbach, U.S. Geological Survey, personal communication).

Dates Arms & Ammunition

License Holders Eligible

Oct. 17-26, 2020* All methods All

Nov. 28 - Dec. 12, 2020** All methods All

Dec. 26, 2020 – Jan. 30, 2021*** All methods All

25

Table 1. Prevalence for fawns, yearlings, and adults from 2016-2018 in Blair, Bedford, and Fulton counties of Disease Management Area 2.

Fawn Yearling ADULT

Both sexes Female Male Female Male

2016 NA 0.9 1.0 1.2 3.8

2017 1.9 2.2 1.5 1.3 5.2

2018 1.8 1.7 2.4 2.9 6.6

Average 1.9 1.7 1.8 2.0 5.5

f) Additional antlered tags: Within Control Units, hunters will be allowed to purchase (at

administrative cost of $2-3) an additional antlered deer tag (may harvest a total of 2 antlered deer). Similar to removing antler point restrictions, additional antlered deer tags will allow hunters more flexibility to harvest additional deer in areas where we need additional CWD samples.

g) Increased allocation of antlerless harvest tags: Hunters can harvest antlerless deer using DMAP permits during any portion of the hunting season. Currently, DMAP units administered by Pennsylvania Game Commission within DMAs allocate 1 permit per 50 acres or 1 permit per 25 acres, depending on the unit. This allocation can be increased in the future to allow more hunters the opportunity to harvest antlerless deer.

5. Consider incentive programs: Incentive programs could be an effective tool to increase land

access for hunters and allow additional deer to be taken in specific areas. During 2019-2020, Pennsylvania Game Commission will survey hunters and landowners to determine if there are incentive programs that would be effective and supported.

6. Special season: Between February and April, if a new CWD case is detected and a Control

Unit created, a 3-week hunting season would be opened to all landowners and any hunters with landowner permission. Additional antlered and antlerless tags will be available during this special season and any legal arms and ammunition (e.g. firearm) may be used.

7. Targeted Removals (as needed): The Pennsylvania Game Commission wants hunters to

have the first opportunity to harvest more deer first. We also want hunters to be the solution and be successful at managing CWD. If the predetermined, minimum sample size quota is not achieved or additional positives are detected, agency-directed targeted removals will occur in Control Units. An adequate number of deer sampled within a CWD Control Unit is necessary to estimate prevalence and spatial distribution of CWD. Targeted removals are small-scale operations, occurring within 3 miles of CWD detections and focused as close to known CWD positive locations as possible. The number of deer removed via targeted removals in each CWD Control Unit will vary depending on the number needed to reach sampling quotas for that area.

a. Additional positive cases: If additional positive cases are detected within a Control Unit, the management objective within that Control Unit will switch from collecting

26

a minimum sample size to reducing deer densities immediately surround the positive cases. Reducing local deer densities will be accomplished through increased hunter harvest and agency-directed targeted removals. The actual number of deer remaining on the landscape to achieve disease management objectives may vary by location. The objective is not to remove all deer from the area. The main objective is to stop the disease before it becomes established in the environment (e.g. in soil). Reducing local deer numbers is the mechanism to achieve the main objectives, not the objective itself. If no further positives are detected in a 3-year period, then deer density, regardless of the number – is acceptable for disease management purposes.

b. Prioritization for targeted removals locations: Factors that will be considered when prioritizing Control Units for targeted removal operations include: spatial proximity to other CWD detections, the number of CWD detections in local area, cervid density in local area, time elapsed since detection, age of sample (CWD-infected cervid), sex of sample, whether sample was a captive or free-ranging cervid, proximity to geographic barriers for dispersal, proximity to Pennsylvania’s elk hunt zones, and effect on DMAs.

Elk Population Considerations The Pennsylvania Game Commission adapts its CWD management actions for elk hunt zones based on the biology of cervid species. CWD can reduce elk survival (Monello et al. 2014). It is the Pennsylvania Game Commission’s responsibility to act in ways to ensure sustainable deer and elk populations for current and future generations. Efforts to reduce the risk of CWD in the elk population help the Pennsylvania Game Commission to meet this responsibility. Our CWD management actions are motivated by an effort to protect both deer and elk and to minimize the impact on deer and elk hunters. At present, the Pennsylvania Game Commission’s response to the discovery of a CWD positive

deer or elk within Pennsylvania’s elk hunt zones is to enclose all the elk hunt zones into a

singular DMA (~2500 sq. mi). The primary motivations for these action are 1) elk are a social

species and movement between generally distinct social units has been documented in

Pennsylvania and in other eastern elk populations (J.E. Banfield, Pennsylvania Game

Commission, personal communication; Rosatte 2017), 2) bull elk in Pennsylvania are known to

travel up to 20 miles for breeding during the annual rut (J.E. Banfield, Pennsylvania Game

Commission, personal communication), and 3) elk have relatively large home ranges compared

to white-tailed deer in Pennsylvania (Table 2; Walter et al. 2018). Thus, elk have the potential

capability of spreading CWD farther distances than white-tailed deer.

27

Additionally, if CWD is detected within the elk management area, management responses will be similar as previously described. One notable difference is that elk will not be taken through targeted removals. Rather, increased hunter opportunity for elk will be allowed in certain areas. The increase in the number of elk tags would depend on the hunt zones where CWD was detected, because population estimates among hunt zones vary. Any elk that disperse out of the elk management area and into a DMA are euthanized to prevent potential spread of CWD back into the elk management area. Additional factors considering our response to CWD infections in elk are: a) elk are generally at much lower densities than deer, b) multiple pregnancies (twins and triplets) are extremely rare in elk (<1%; Kittams 1953; Flook 1970; Houston 1982), c) the population estimate of elk in Pennsylvania, about 1,000 elk (Pennsylvania Game Commission, 2019), is relatively low and thus ecologically fragile compared to deer in Pennsylvania.

Conclusion CWD is a serious, long-term threat to deer and elk in Pennsylvania. Without change and further management action, CWD will continue to spread and increase in Pennsylvania. It is the responsibility of hunters, landowners, Pennsylvania Game Commission, and many others to take action to manage CWD effectively. Despite the continued increase of CWD in Pennsylvania, successes from other states provide hope and guidance. With swift and effective management actions we can slow the spread and reduce prevalence of CWD. To be successful, it will take support and participation from all interested stakeholders, with responsibility and effort from landowners and hunters being crucial.

Species/Sex Mean (sq. mi) SD n

Female WTD1 0.74 0.51 49

Male WTD1 1.75 0.87 12

Female ELK 6.65 2.24 13

Male ELK 11.23 3.21 14

1 Data summarized across 5 study areas in Pennsylvania (Walter et al. 2018)

Table 2. Average home ranges (95%) for

white-tailed deer and elk in Pennsylvania.

28

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Appendix 1: Distance Sampling to Estimate Deer Abundance The Pennsylvania Game Commission and the Pennsylvania Cooperative Fish and Wildlife Research Unit (PACFWRU) at Penn State have studied different methods of estimating abundance of white-tailed deer over the past 30 years. Methods vary in time and money required and every method has assumptions that need to be met before it will provide accurate estimates of abundance. Distance sampling is a method of estimating deer abundance that has been used for many species (Buckland et al. 2001) and is being used on current studies in Pennsylvania (https://ecosystems.psu.edu/research/projects/deer/news/2018/distance-sampling). The Game Commission and PACFWRU are studying the use of distance sampling from roads using window-mounted Forward-Looking infrared (FLIR) units. The FLIR units increase the probability of observing deer, but still are affected by the amount of vegetation and distribution of deer (Figure 1). The premise of distance sampling is that no matter how deer are distributed on the landscape, if you randomly place transects across the landscape deer will be uniformly distributed with respect to the transects. In other words, if you randomly place transects across the study area, you will just as likely find a deer 10 feet from the transect as 200 feet from the transect.

Figure 1. Infrared images of white-tailed deer in Bald Eagle State Forest, May 2019, obtained

during a study to develop methods of using vehicle-based FLIR surveys to estimate deer

abundance. Detection probabilities of deer can be increased using FLIR, but the further a deer is

from a road the less likely it will be detected. Distance sampling methods can adjust for this

problem.

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The problem, however, is that a deer 200 feet from the transect is less likely to be detected (because of trees, topography, etc.) than a deer 10 feet from the transect. This problem is a detection issue and distance sampling estimates a detection probability and adjusts the observed count of deer to estimate the total number of deer on the study area. In the graph below (Figure 2), the vertical bars represent the relative number of deer observed at different distance intervals and the line represents the detection probability for a given distance from the transect. Notice how detection probability is 1.0 (100%) on the transect line (distance = 0.00 km) and declines rapidly until no deer were observed beyond 60 meters from the transect line (distance = 0.06 km).

Figure 2. Relative number of deer observed (bars) and the calculated detection probability (line)

of deer by distance (km) from the transect line.

To conduct a distance sampling survey, there are 4 pieces of information that are needed: (1) the size of the study area (A), (2) the length of transects surveyed (L) (3) the perpendicular distances from the transect each deer group was detected, and (4) the number of deer in each group detected. The length of the transect and the greatest distance a deer was observed (w) is used to calculate the area surveyed (2 × L × w = a) and the distances deer were detected are used to estimate the probability of detecting a deer (p) within the area surveyed. If the total number of deer observed is n, then an estimate of the number of deer in the study area (N) is:

�̂� = 𝐴𝑛

𝑎�̂�

36

An important assumption of distance sampling cannot be met using roads to survey deer. This assumption is violated because deer are less likely to be observed near roads (Figure 3). Estimates of abundance can still be obtained, but they will underestimate deer abundance (Marques et al. 2013). Additional information on distance sampling can be found at http://distancesampling.org/

Figure 3. Locations of deer fitted with GPS collars relative roads on the chronic wasting disease

management area in south-central Pennsylvania, April 2018. Deer are less likely to be observed

within 50 meters of a road.

Literature Cited Buckland, S.T., D. R. Anderson, K. P. Burnham, J. L. Laake, D. L. Borchers, and L. Thomas. 2001.

Introduction to distance sampling: estimating abundance of biological populations. Oxford University Press, Oxford, U.K.

Marques, T. A., S. T. Buckland, R. Bispo, and B. Howland. 2013. Accounting for animal density

gradients using independent information in distance sampling surveys. Statistical Methods and Applications 22:67-80.

Stainbrook, D. P. 2011. Methods of estimating white-tailed deer abundance at Gettysburg

National Military Park: testing assumptions of distance sampling. M.S. Thesis, Pennsylvania State University, University Park, USA.