Monitoring of Alligator ( spatula) Reintroduced into Merwin Preserve

Nathan Grider - University of Illinois, Springfield Rob Hilsabeck - Illinois Department of Natural Resources Status • Populations have declined

• Vulnerable to extinction

• Reintroduction in AL, AR, FL, KY, LA, MS, MO, OK, TN, and TX

M.D. W. F. P

Field & Stream River Monsters

Jeremy Wade and Mark Spitzer with a 7 ft, 111 lb http://colourofautumn1216.blogspot.com/2010/06/river-monsters.html History In Illinois

• Last vouchered record from 1966

• Delisted in 1994 (extirpated)

• Reintroduction efforts began in 2009 by IDNR Kaskaskia River

Why Reintroduce Them? • Increase biodiversity – resist invasion

• Apex predators provide top-down control

• May control “rough fish” and invasive species

• May help prevent stunting of sportfish

• Popular food fish

• Angling and bowfishing

Big Fish Bowfishing ™ Merwin Preserve (Spunky Bottoms)

• Approximately 590 ha

• 100 alligator gar were tagged with passive integrated transponders (PIT), released 9/29/2011

• Average length was 538 mm and weight 886 g

Objectives 1) Measure growth rate and compare to data from the southern range

2) Determine condition (fitness) and compare to data from the southern range

3) Investigate prey selection and potential use as a management tool

4) Compare sampling methods used to capture alligator gar

Methods

Sampling • Sampled May - October = six events

• Sample event = two days and one night of extensive gear effort

Gears • Modified multifilament gill nets – 3” bar mesh, dyed black

• Experimental monofilament gill nets

• Trap nets, 1.5” mesh

• Mini fyke nets

• DC Electrofishing

Diet Analysis

• Gastric lavage

• Strauss (1979) index used to determine prey selection

• Compares abundance of prey items in diet to abundance in environment -1 = avoidance/inaccessibility, 0 = no selection (opportunistic) +1 = selection

Results

American Fisheries Society Catch Frequency, All Gears, All months

30 N = 6,911 28 26 24 22 20 18

16

14 12 10

Frequency % Frequency 8 6 4 0.25 2 0 Length and Mass Gain

1000 7

(t(17) = -13.48, p < 0.001) 6 800

5

600 4

400 3 Mass (kg) Mass

Length (mm) Length 2 200 1 (t(17) = -10.39, p < 0.001)

0 0

Length

Mass

4/1/2012

9/14/2011 11/3/2011 2/11/2012 5/21/2012 7/10/2012 8/29/2012 12/7/2012

12/23/2011 10/18/2012 Growth Rates and Water Temperature

40 0.2

r(4) = 0.84, p < 0.05)

35 SGR

0.15

30

C °

25 0.1

Length/Mass Length/Mass 20

0.05 Water Temp. Temp. Water 15 (r(4) = 0.80, p = 0.07)

10 0

Mean Water Temp. (°C)

6/5/20120:00 8/4/20120:00

4/26/2012 0:00 4/26/2012 0:00 5/16/2012 0:00 6/25/2012 0:00 7/15/2012 0:00 8/24/2012 0:00 9/13/2012 0:00 10/3/2012 Length SGR

Mass SGR Growth Rate: Illinois and

0.08

0.07 0.06

0.05 (% /Day) (%

IL 0.04 0.03 LA 0.02 (t(42) = -5.54, p = 0.13 Length SGR SGR Length 0.01 0 0 200 400 600 800 1000 1200 TL (mm)

0.3

0.25

/Day) 0.2

0.15 IL 0.1

Mass SGR (% (% SGR Mass LA 0.05 (t(42) = -1.49, p = 0.14 0 0 1 2 3 4 5 6 7 Mass (kg) Length Gain: Illinois and Louisiana

1100

1000

900

800 IL 700

TL (mm) TL LA 600

500

400

300 350 400 450 500 550 600 Age in days Body Condition: Illinois and Louisiana

4

3.5

3 IL Merwin Preserve (n = 18)

LA Port Sulphur (n = 54) Mass (g) Mass

10 2.5 LA Bayou Dularge (n = 48) Log

Log Mass = 3.7654 (Log Total Length) - 7.4777 2 10 10 n = 120 R² = 0.98 p < 0.01

1.5 2.5 2.6 2.7 2.8 2.9 3 3.1

Log10 TL (mm)

Diets

Diet Content Frequency 100%

90%

80%

70%

60% Unknown Fish 50% Gizzard Shad 40% Empty

30%

20%

10%

0% Shortnose Alligator Gar Estimating Prey Length from Remains

• Knowing prey size allows us to estimate predator impact

• How do we estimate prey length from diet remains?

• Use linear relationship of eye diameter or caudal peduncle to total length (Scharf et al. 1997). Prey Size selection

y = 0.0831x + 0.2483 Gizzard Shad R² = 0.9523 35 Mean 20.3 ± 1.1 n = 339 y = 0.0324x + 4.1315 30 R² = 0.7872 Mean 12.0 ± 1.0 25

20 Eye Diameter Caudal Peduncle 15 Linear (Eye Diameter)

10 Linear (Caudal Peduncle)

5 Caudal Peduncle from Alligator Gar

Diet Eye Diameter/Caudal Peduncle (mm) Peduncle Diameter/Caudal Eye 0 Caudal Peduncle from Shortnose 0 50 100 150 200 250 300 350 400 Gar Diet

Total length mm

41% of Predators Length Diet Contents Over Time

Alligator Gar Diets Over Time 8

7

6

5 Gizzard Shad 4 Unknown Fish

3 Empty Samples Collected Samples 2

1

0 May (2) June (2) July (1) August (1) September (4) October (7)

Shortnose Gar Diets Over Time 8 7

6 5 Gizzard Shad 4 Unknown Fish 3 Empty

Samples Collected Samples 2 1 0 May (0) June (1) July (1) August (5) September (7) October (7) Food Selection Index 1 0.8 0.6 0.4

0.2

0 Score

-0.2 L -0.4 -0.6 -0.8 -1 May/June July/August September/October Ameiurus -0.0649 -0.078 -0.1688 Bigmouth Buffalo -0.0119 -0.0395 -0.063 Common Carp -0.2727 -0.3192 -0.529 Gizzard Shad 0.68515 0.74139 -0.0504 Largemouth Bass -0.1862 -0.0968 -0.0554 Lepomis -0.341 -0.1774 -0.063 Pomoxis -0.0586 -0.0305 -0.0705 +1 = Selection 0 = No selection (opportunistic) -1 = Avoidance/inaccessibility

Prey Abundance Over Time

July & August Electrofishing CPUE

20 15 Common Carp 10 Gizzard Shad 5 Lepomis

Catch/Hour 0

Largemouth Bass

40 90

190 240 290 340 390 440 490 550 140 Pomoxis Total Length (mm)

September & October Electrofishing CPUE

20

15 Common Carp 10 Gizzard Shad

5 Lepomis Catch/Hour

0 Largemouth Bass

40 Pomoxis

100 150 200 250 300 350 400 450 500 550 630 Total Length (mm) June October Recapture Success and Mortality

Alligator Gar: Gear Mortality 7

6

5

4 Lived

catch 3 Mortality

2

1

0 Modified Gill (6) Experimental Gill (2) Trap (8) Electrofishing Modified (1) • May – August: Mortality = 50%

• September – October Mortality = 38% Discussion Objective 1 & 2 • No significant difference in growth rate or condition compared to Louisiana • Factors that effect growth rate: salinity, temp., prey, and habitat Objective 3 • No sportfish found in diet. • Did they eat a few? Probably.

• Selection or opportunistic feeding on gizzard shad? “Optimal Foraging Theory”

Some Diet Predictions

300

250 Bigmouth Buffalo

200 Common Carp Largemouth Bass 150

Gizzard Shad Total catch Total 100 Ameirus 50 Pomoxis

0 200 210 220 230 240 250 260 270 280 290 300 310 320 TL (mm) Abundance of potential prey items at Merwin Preserve within the preferred prey size range (200 – 320 mm) of 137 – 183 cm alligator gar described by Goodyear (1967). Discussion

Objective 4 • Trap nets and modified gill nets worked best

• Modified gill nets produced less bycatch, but higher mortality

• Sampling in September & October is recommended

DC Electrofishing

• 3,500 watt generator (small boat) = no Alligator Gar

• 5,000 watt generator (big boat) = 8.5 hours produced 1 Alligator Gar @ 30 cycles/sec & 7 amps

What’s Next?

• Continue reintroduction and monitoring • Consider further harvest restrictions • Public education and outreach • Maybe develop catch and releasing fishing opportunities in dedicated waters Could help fund continued conservation work! Bass Pro Shop - Springfield, MO Acknowledgments

Illinois Department of Natural Resources Rob Hilsabeck Trent Thomas Illinois Natural History Survey Dr. Leon Hinz Doug Carney Nerissa Michaels Matt O’Hara Levi Solomon Rich Lewis John Wisher Karen Miller The Nature Conservancy Todd Rettig Tharran Hobson Nate Goetten

Dr. Michael Lemke - Thesis Advisor Literature Cited

Brinkman, E. L. 2008. Contributions to the life history of alligator gar (Atractosteus spatula, lacepede), in Oklahoma. Master’s Thesis, Oklahoma State University. Oklahoma City, Oklahoma

Garcia De Leon, F. J., L. Gonzalez-Garcia, L. M. Herrera-Castillo, K. O. Winemiller, & A. Banda- Valdes. 2001. Ecology of the alligator gar, Atractosteus spatula, in the Vicente Guerrero Reservoir, Tamaulipas, Mexico . The Southwestern Naturalist 46(2):151-157

Ianni, R. C. 2011. Monitoring diets and growth rates of native predatory fish stocked to suppress non-native tilapia. Master’s Thesis, Nicholls State University. Thibodaux, Louisiana

Scharf, F. S., J. A. Buckel, F. Juanes, & D. O. Conover. 1997. Estimating piscine prey size from partial remains: Testing for shifts in foraging mode by juvenile bluefish. Environmental Biology of Fishes 49: 377-388

Strauss, R. E. 1979. Reliability estimates for Ivlev’s Electivity Index, the forage ratio, and a proposed linear index of food selection. Transactions of the American Fisheries Society 108: 344-352