Transcript presentation on turtles

Challenges Facing Iowa’s Turtle Populations
Chad R. Dolan
Iowa DNR Southeast Regional Office
110 Lake Darling Road
Brighton, IA 52540
Iowa’s Harvestable Turtle Species
Food
Why are turtles in decline?
1. Habitat Loss & Degradation
2. Exotic/Invasive Species
3. Environmental Pollution
4. Disease
5. Global Climate Change
6. Unsustainable Use Without
Proper Management
(Ernst & Lovich 2009)
1. Habitat Loss & Degradation
Road fragmentation
Wetland destruction
Noted w/ regards to Turtles in Iowa by
Vandewalle & Christiansen (1996)
Water Quality Degradation
Damage to River Systems
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 harvest
X Limited waters
X Season, size limits, other rules
X- Ontario
X
X
X
X
X
X
X
X
X
IOWA
X
X
X
X
X
X
Life History Characteristics
Iowa’s Harvestable Species
 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
Reproductive Potential: A Comparison of Iowa Species
350
300
Number of individuals
308
Bobcats
Snapping Turtle
White-Tailed Deer
Bobcat
250
200
150
100
43 Whitetails
50
1 Snapper
35 eggs
0
0
2
4
6
Year
8
10
Number
Iowa Commercial Turtle Harvesters by Year
Maximum = 179 in 2012
200
180
160
140
120
100
80
60
40
20
0
Year
Snapper Total Annual Harvest
Maximum = 203,156 lbs. in 2007
Harvest (lbs.)
250,000
200,000
150,000
100,000
Most harvested turtle
species since 1987
(3,210,400 lbs.)
50,000
0
Year
Snapper Average Harvest Per Licensee
Harvest (pounds)
Slight decrease of ~ 10 lbs. per harvester per year
2,000
1,800
1,600
1,400
1,200
1,000
800
600
400
200
0
Year
Harvest (pounds)
Softshell Total Annual Harvest
Maximum = 46,496 in 2002
50,000
45,000
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
Year
Softshell Average Harvest Per Licensee
Decreasing trend in last 14 years
Harvest (pounds)
700
600
500
400
300
200
100
0
Year
Common Snappers Harvested by County
Lyon
Osceola
Sioux
O'Brian
Plymouth
Dickinson
Cherokee
Woodbury
Emmit
Palo
Bueno V
Pocahont
Sac
Ida
Winneb
Kossuth
Clay
Humbolt
Mitchell
Howard
Cerro
Floyd
Chichasaw
Wright
Franklin
Butler
Bremer
Hamilton
Hardin
Blackhawk
Webster
Calhoun
Worth
Hancock
Grundy
Winni
Allamake
Fayette
Clayton
Buchan
Deleware
Dubuque
Jackson
Monona
Crawford
Greene
Carrol
Tama
Marshall
Story
Boone
Jones
Benton
Linn
Iowa
Johnson
Clinton
Cedar
Harrison
Shelby
Audabon
Dallas
Guthrie
Polk
Jasper
Powesheik
Scott
Muscatine
Pottawattamie
Adair
Cass
Madison
Warren
Marion
Mahaska
Keokuk
Wash
Louisa
Fremont
Montgum
Adams
Union
Clarke
Lucas
Page
Taylor
Ringold
Decatur
Wayne
Monroe
Wapello
Jefferson
Davis
Van Burren
Henry
Des Moines
Mills
Appanoose
Lee
Snapper Numbers Harvested by County 2014
0 - 29
30 - 59
60 - 99
100 - 199
200 - 831
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.
Turtle Catch in Southeast Iowa (2010-2014)
2%
1%
34%
Painted Turtle
Common Snapper
Spiny Softshell
35%
6%
22%
Red-Eared Slider
Smooth Softshell
Other
Snapper Relative Frequency (2010-2014)
Relative frequency (%)
40
Male
30
N=103
20
11.4 in.
13.0 lbs.
IA Record–
Maximum
Size
23
13
10
2
4
8
16
12
9
9
3
1
0
1
3
5
7
9
11
13
15
17
19
40
Female
30
31
N=112
US/Canada
Record–
Maximum Size
25
20
11
10
10
2
2
2
2
3
5
4
2 1
0
1
3
5
7
9
11
13
15
17
Straight-line carapace length (inches)
19
Can Iowa’s turtle populations sustain themselves,
long-term, given the challenges they’re facing?