Alligator Gar in Texas’ Coastal Zone: Insights from Otolith Microchemistry and Genetic Analyses
D. J. Daugherty1, K. L. Pangle2, W. Karel3, C. R. Robertson1, N. Boyd3, D. Buckmeier1, N. Smith1, and F. Baker2
1 Texas Parks and Wildlife Department, Inland Fisheries Division
2 Department of Biology, Central Michigan University
3 Texas Parks and Wildlife Department, Coastal Fisheries Division Why Alligator Gar?
• Biodiversity Why Alligator Gar?
• Biodiversity
• Periodic strategist
• Long lived > 50 y
• Late maturing (5–10 y)
2,572 mm TL 148 kg 02/14/2011 Chotard Lake, MS Why Alligator Gar?
• Biodiversity
• Periodic strategist
• Apex predator • Community structure • Invasives Why Alligator Gar?
• Reduced range
• Native to 14 states
• Extirpated from 6
Historic Current Why Alligator Gar?
• Reduced range
• Native to 14 states
• Extirpated from 6
Mark Spitzer Photo Why Alligator Gar?
• Texas • Stronghold
• Trophy fisheries Why Alligator Gar?
• Texas • Increased publicity
• Increased pressure Why Alligator Gar?
• Conservation value
• Recreational/economic value
• Active management (2009)
• Priority species for research Movement/Habitat Use
• Lower Trinity River
• Tagged 51 fish
• 22-month study Movement/Habitat Use
• Lower Trinity River Texas
0% • Tagged 51 fish
• 22-month study 78%
Galveston Bay
Gulf of Tagging site Mexico Movement/Habitat Use
• Lower Trinity River Texas
0% • Tagged 51 fish
• 22-month study 78%
Galveston • >2,000 caught in bay Bay Gulf of Tagging site Mexico Movement/Habitat Use
TEXAS Sabine Lake (8,590) Galveston Bay (2,115) Matagorda Bay East Matagorda (2,109) Bay Aransas (2,053) Bay San Antonio (5,029) Bay (3,227) Corpus Christi Bay (655)
Upper Laguna Madre (105)
Lower Laguna Gulf of Mexico Madre (660) Coastal River Populations
• Discrete stocks? Texas
“River” stock
“Bay” stock
Galveston Bay
Gulf of Mexico Coastal River Populations
• Discrete stocks? Texas
• Mixed stock?
• Management scale
Galveston Bay
Gulf of Mexico Coastal River Populations
• Discrete stocks?
• Mixed stock?
• Management scale
• Importance of bay habitats Coastal River Populations
• Lower Guadalupe River TEXAS
Gulf of Mexico Coastal River Populations
• Otolith microchemistry
• Cost effective
• Lifetime record
• “Novel” for gar Otolith Microchemistry
• Laser Ablation • ICPMS • Elemental signatures Otolith Microchemistry Otolith Microchemistry
10 8 6 4 2 0
Objectives
• Evaluate efficacy of otolith microchemistry in differentiating Alligator Gar habitat use in coastal systems
• Characterize movement, habitat use and potential for stock structuring
• Compare results to genetic analyses Fish Collection Fish Collection
• Catch location
• Total length
• Sex
• Otoliths
• Fin clip Otolith Microchemistry
• Laser Ablation ICP-MS
• Core-to-edge transect
• Pulse rate: 12Hz
• Spot size: 40µm
• Pass rate: 20 µm/s Otolith Microchemistry
• SW/FW signature
• LDFA
• Otolith edge
• Bay vs. middle/upper river fish
• Suite of 8 elements - Sr
• Applied across transects
• Historic water chemistry consistent and expected Genetics
• Microsatellites (14 loci)
• Mitochondrial DNA
• Structuring
• Catch location
• Chemistry data Results
10.0
7.5 N = 151 fish 5.0 Bay Males = 621 -1,515 mm Females = 1,058 – 2,173 mm 2.5
0.0 Number of fish of Number 10.0
7.5 Edge classification accuracy
5.0 River River 100%
2.5 Bay 93%
0.0 1 2 3 Strontium (mmol/molCa) River Fish Lower River
3.5 Female, 1,427 mm TL 3.5 Female, 1,918 mm TL
3.0 3.0
2.5 2.5
2.0 2.0
1.5 1.5
1.0 1.0 Otolith Sr:Ca (mmol/mol) OtolithSr:Ca Otolith Sr:Ca (mmol/mol) OtolithSr:Ca 0.5 0.5
0.0 0.0 0 1208 2416 3623 4831 6039 0 1235 2469 3704 4938 6173 Distance from core (um) Distance from core (um) River Fish Lower River
3.5 Female, 1,427 mm TL 3.5 Female, 1,918 mm TL
3.0 3.0
2.5 2.5
2.0 2.0
1.5 1.5
1.0 1.0 Otolith Sr:Ca (mmol/mol) OtolithSr:Ca Otolith Sr:Ca (mmol/mol) OtolithSr:Ca 0.5 0.5
0.0 0.0 0 1208 2416 3623 4831 6039 0 1235 2469 3704 4938 6173 Distance from core (um) Distance from core (um) 32% 68% River Fish Middle River
3.5 Female, 2,047 mm TL 3.5 Female, 2,069 mm TL
3.0 3.0
2.5 2.5
2.0 2.0
1.5 1.5
1.0 1.0 Otolith Sr:Ca (mmol/mol) OtolithSr:Ca Otolith Sr:Ca (mmol/mol) OtolithSr:Ca 0.5 0.5
0.0 0.0 0 1432 2865 4297 5730 7162 0 1535 3070 4605 6140 7675 Distance from core (um) Distance from core (um) 52% 48% River Fish Upper River
3.5 Female, 1,551 mm TL 3.5 Female, 1,551 mm TL
3.0 3.0
2.5 2.5
2.0 2.0
1.5 1.5
1.0 1.0 Otolith Sr:Ca (mmol/mol) OtolithSr:Ca Otolith Sr:Ca (mmol/mol) OtolithSr:Ca 0.5 0.5
0.0 0.0 0 1133 2267 3400 4534 5667 0 990 1980 2971 3961 4951 Distance from core (um) Distance from core (um) 70% 30% Likelihood of Bay Use
• Related to catch location, sex, or size(age)?
• Multiple logistic regression
• Catch location(rkm)
• Sex
• TL
• All interactions
• Catch location (P = 0.018) Bay Fish
3.5 Male, 1,109 mm TL, Hynes Bay 3.5 Male, 1,062 mm TL, Hynes Bay
3.0 3.0
2.5 2.5
2.0 2.0
1.5 1.5
1.0 1.0 Otolith (umol/mol) Sr:Ca Otolith Sr:Ca (mmol/mol) OtolithSr:Ca 0.5 0.5
0.0 0.0 0 744 1488 2233 2977 3721 0 907 1814 2722 3629 4536 Distance from core (um) Distance from core (um) 93% 7% Anomalies
4.0 Female, 1,432 mm TL, Upper River
3.5
3.0
2.5
2.0
1.5
1.0 Otolith (mmol/mol) Sr:Ca 0.5 5.0 Female, 1,547 mm TL, Lower River 0.0 0 837 1674 2511 3348 4185 4.5
Distance from core (um) 4.0
3.5
3.0
2.5
2.0
1.5 Otolith (mmol/mol) Sr:Ca
1.0
0.5 0 1153 2307 3460 4614 5767 Distance from core (um) Spatial Patterns
River resident Transient Bay resident 100 90 80 70 60 50 40 Frequency (%) Frequency 30 20 10 0 Upper river Middle river Lower river Bay (n = 27) (n = 20) (n = 47) (n = 57) Sampling reach Microsatellite Analyses
1 1 1 (12) (39) Guadalupe Bay 2 Hynes Bay 2 San Antonio Bay 2 8% 10% 3% (21) 17% 3 3 3 10% 24% 4 26% 4 4 28% 42% 33% 5 5 33% 5 33% 33% 6 6 6 7 7 7 Hd=0.742 Hd=0.752 Hd=0.748
1 1 1 5% Lower River (62) Middle River (21) Upper River (38) 2 2 2 3% 5% 5% 5% 3% 3 3 8% 5% 3 21% 33% 29% 4 4 19% 4 32% 21% 39% 5 5 5 33% 34% 6 6 6 7 7 7 Hd=0.764 Hd=0.771 Hd=0.716 Mitochondrial Analyses
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0% 1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101 105 109 113 117 121 125 129 133 137 141 145 149 153 157 161 165 169 173 177 181 185 189 193 197 GB HB SB LR MR UR (1-12) (13-51) (52-73) (74-141) (142-162) (163-200) Summary
• Technique shows promise Summary
• Technique shows promise
• Life-history variation exists
• Well adapted for environmental stochasticity Summary
• Technique shows promise
• Life-history variation exists
• Limited spatial structuring
• No significant genetic structuring
• Management likely best at system scale
• “Jurisdictional overlap” Summary
• Technique shows promise
• Life-history variation exists
• Limited spatial structuring
• No significant genetic structuring
• Management likely best at system scale
• “Jurisdictional overlap” • Telemetry truly a snapshot Future Directions
• Age estimation
• Links to hydrology and environment
3.5 Female, 1,551 mm TL
3.0
2.5
2.0
1.5
1.0 Otolith Sr:Ca (mmol/mol) OtolithSr:Ca 0.5
0.0 0 990 1980 2971 3961 4951 Distance from core (um) Inland Fisheries Coastal Fisheries F-231-R Administrative Resources Texas Parks and Executive Office Wildlife Department