challenges facing iowa’s turtle populations chad r. dolan iowa dnr southeast regional office 110...
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![Page 1: Challenges Facing Iowa’s Turtle Populations Chad R. Dolan Iowa DNR Southeast Regional Office 110 Lake Darling Road Brighton, IA 52540](https://reader035.vdocuments.net/reader035/viewer/2022062806/5697bfa31a28abf838c966de/html5/thumbnails/1.jpg)
Challenges Facing Iowa’s Turtle Populations Chad R. Dolan
Iowa DNR Southeast Regional Office110 Lake Darling Road
Brighton, IA 52540
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Food
Iowa’s Harvestable Turtle Species
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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)
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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020406080
100120140160180200
Iowa Commercial Turtle Harvesters by YearMaximum = 179 in 2012
Nu
mb
er
Year
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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
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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
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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
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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
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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.
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Painted TurtleCommon SnapperSpiny SoftshellRed-Eared SliderSmooth SoftshellOther
6%
34%
22%
2% 1%
Turtle Catch in Southeast Iowa (2010-2014)
35%
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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.
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Can Iowa’s turtle populations sustain themselves, long-term, given the challenges
they’re facing?