Challenges Facing Iowa’s Turtle Populations Chad R. Dolan

Iowa DNR Southeast Regional Office110 Lake Darling Road

Brighton, IA 52540

Food

Iowa’s Harvestable Turtle Species

1. Habitat Loss & Degradation

2. Exotic/Invasive Species

3. Environmental Pollution

4. Disease

5. Global Climate Change

6. Unsustainable Use Without Proper Management

Why are turtles in decline?

(Ernst & Lovich 2009)

1. Habitat Loss & Degradation

Road fragmentation

Wetland destruction

Water Quality Degradation

Damage to River Systems

Noted w/ regards to Turtles in Iowa by Vandewalle & Christiansen (1996)

2. Exotic/Invasive Species 2,300 exotic species have

been established in the U.S., nearly 7.7 species per decade

Habitats change & plant community organization is modified

Delicate relations between plants & animals are altered or eliminated

Invasive doesn’t always mean exotic

Numerous native turtle nest and hatchling predators flourish in human-altered landscapes

3. Environmental Pollution

Turtles: Can accumulate arsenic,

mercury, other heavy metals, organochlorines, radionucleotides, and crude oil

Can be poisoned by pesticides or via consuming non-food items that mimic prey

• Death

• Sterility

• Sex ratio effects

4. Disease

Can cause shell lesions; degree of necrosis can be shocking

Causes are not well understood

Disease outbreaks can reduce survival

Potentially severe effects on turtle populations

Been known to affect red-eared slider, painted turtle, common snapping turtle, & stinkpot

5. Global Climate Change

Recently, some scientists have suggested that global climate change has the potential to eliminate the production of male offspring if average global temps increase 4º C (2.2º F) and that increases of less than 2º C (1.1º F) may dramatically skew sex ratios (Janzen 1994)

Also, because turtles are ectothermic (cold-blooded), their digestion rate, growth, reproduction, and activity are all closely related to temperature

Changing water levels in river, lakes, and wetlands may impact nesting sites and habitat

6. Unsustainable Use Without Proper Management Sport Harvest - collection of small to

intermediate size turtles for pets or larger turtles for food (domestic use)

Commercial Harvest – collections to supply the pet or food trade (domestic and international markets – particularly Asia; Mali et al. 2014) and broodstock for aquaculture units

In combination – harvest has resulted in the removal of many adults from populations

Gathering of eggs and juveniles - for commercial or domestic use reduces the rate of replacement of those adults left to die in the wild

Many scientists believe - that given slow rates of maturation and reproduction, turtles cannot withstand exploitation and still maintain their numbers

X No commercial turtle harvestX Limited watersX Season, size limits, other rules

X

XX

X

X X

X

X

XXX

X

X- Ontario

XX

X

IOWA

Life History Characteristics

Longevity (Ersnt & Lovich 2009)

• 20-60 years (varies by spp.)

Age at Maturity (Ersnt & Lovich 2009; LeClere 2013)

• 4-5 years for males, 7-10 years for females

Clutch Sizes (Ersnt & Lovich 2009; LeClere 2013)

• 9-35 eggs /clutch , 1-2 clutches per year (varies by spp.)

Annual Predation Rates (Ernst & Lovich 2009)

• 55%-100% in some years (varies by spp.)

• Recently laid nests more susceptible than older ones

• Rainfall or use of preferred nesting areas can reduce predation

• Can result in low recruitment

• Exploitation Rates (Zimmer-Shaffer et al. 2014)

• Snappers: ≤2.3% to maintain a stationary population

• Softshells: no harvest can be sustained

Iowa’s Harvestable Species

Reproductive Potential: A Comparison of Iowa Species

Year

0 2 4 6 8 10

Num

ber

of in

div

idual

s

0

50

100

150

200

250

300

350

Snapping Turtle White-Tailed Deer Bobcat

308 Bobcats

43 Whitetails

1 Snapper35 eggs

020406080

100120140160180200

Iowa Commercial Turtle Harvesters by YearMaximum = 179 in 2012

Nu

mb

er

Year

0

50,000

100,000

150,000

200,000

250,000

Snapper Total Annual HarvestMaximum = 203,156 lbs. in 2007

Harv

est

(lb

s.)

Most harvested turtle species since 1987

(3,210,400 lbs.)

Year

Year

Harv

est

(pou

nd

s)

Snapper Average Harvest Per Licensee

0200400600800

1,0001,2001,4001,6001,8002,000

Slight decrease of ~ 10 lbs. per harvester per year

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

2007

2009

2011

2013

2015

05,000

10,00015,00020,00025,00030,00035,00040,00045,00050,000

Harv

est

(pou

nd

s)

Year

Softshell Total Annual HarvestMaximum = 46,496 in 2002

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

2007

2009

2011

2013

2015

0

100

200

300

400

500

600

700

Harv

est

(pou

nd

s)

Year

Softshell Average Harvest Per LicenseeDecreasing trend in last 14

years

Common Snappers Harvested by County

Snapper Numbers Harvested by County 20140 - 2930 - 5960 - 99100 - 199200 - 831

Adair

Lyon Osceola

Sioux

Plymouth

O'Brian

Winni Allamake

Clayton

Kossuth

Polk

Story

Jasper

Warren

Dallas

Dubuque

Jackson

Clinton

Union

Scott

Muscatine

Davis

Guthrie

Boone

Howard

Marshall

Fremont

Mills

Louisa

Des Moines

Lee

Adams

Cedar

JohnsonIowa

Woodbury

Monona

Powesheik

Jones

Henry

Wash

Jefferson

Van Burren

Fayette

DelewareBuchan

LinnBenton

Blackhawk

Tama

Chichasaw

Bremer

Marion

MitchellWorth

CassPottawattamie Madison

Dickinson Emmit

Ida Sac

Wright

Hamilton HardinGrundy

Winneb

Hancock Floyd

Butler

Audabon

Franklin

Cerro

Humbolt

WebsterCalhoun

Pocahont

PaloClay

Shelby

Montgum

Crawford Carrol Greene

Cherokee Bueno V

Harrison

Keokuk

Taylor Ringold Decatur

Mahaska

Wayne AppanoosePage

Clarke Lucas Monroe Wapello

2008-2013

2014

Historically, much of the turtle harvest has occurred in southeast Iowa. A slight shift to south-central Iowa was observed in 2014.

Painted TurtleCommon SnapperSpiny SoftshellRed-Eared SliderSmooth SoftshellOther

6%

34%

22%

2% 1%

Turtle Catch in Southeast Iowa (2010-2014)

35%

1 2 3 4 5 6 7 8 9 10111213141516171819200

10

20

30

40

2 4 38

139

16

23

129

1

MaleN=103

IA Record–Maximum

Size

1 2 3 4 5 6 7 8 9 10111213141516171819200

10

20

30

40

2 2 2 2 3 5 4

10

25

31

11

2 1

N=112 US/Canada Record–

Maximum Size

Straight-line carapace length (inches)

Rela

tive f

req

uen

cy

(%)

Snapper Relative Frequency (2010-2014)

Female

11.4 in.13.0 lbs.

Can Iowa’s turtle populations sustain themselves, long-term, given the challenges

they’re facing?