How fish otoliths can be used as a forensic tool
Sam BourretFisheries Biologist
Montana Fish, Wildlife, & Parks
What is a fish otolith? (Greek: ōto ‐ ear líth – stone)
Photo credit: uni.hi.is/scampana/otoliths
Photo credit: awesomeocean.com
How is the otolith a forensic tool?
Unique geochemical signatures
Photo credit: dnr.sc.gov
87Sr/86Sr Sr/Ca Ba/Ca
Brandon McMahon Photography
Methods
0.700
0.705
0.710
0.715
0.720
0.725
0.730
0.735
87Sr / 86Sr
Otolith core ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Otolith edge
Age 1 annuli
How many illegal fish introductions?
Invasive Fish Impacts
Northern Pike ‐ AlaskaAsian Carp ‐Mississippi River
Snakehead ‐Potomac River
Native species
Forensic case studies in Montana
• Walleye in Swan Lake
• Northern Pike in Lake Mary Ronan
Swan Lake
Joel Sartore/National Geographic stock with Wade Fredenberg
Crime Scene – Swan Lake, October 2015• N = 2, 17 and 17.5 inch immature males
Were the walleye born in Swan Lake? If not, when and where were they transported from?
Evidence: Born in Swan Lake?
Distance from otolith core (UM)
87Sr/8
6 Sr
Distance from otolith core (UM)
June 2015
87Sr/8
6 Sr
Evidence: Born in Swan Lake?
Water Body Angler Days Distance to Swan lake (road km)Canyon Ferry 3983 299Fort Peck Res. 3962 742Holter 1510 253Tiber 1078 360Fresno 906 444Nelson Res. 881 631Cooney Res. 776 616Frances 657 432Hauser 589 298Tongue River Res. 415 929Bighorn Res. 340 851Lake Helena 228 309Noxon Rapids Res. 103 261
Evidence:Where were they born?
Statistical Analysis
• DFA – predict which group?
• 95% ‐ leave‐one‐outcross validation
• Classified with 97% and99% posterior prob.
When And Where Did the Crime Occur
Crime scene – Lake Mary Ronan (LMR)
Past Illegal Fish Introduction in Lake Mary Ronan• Missoulian, August 19, 1992
• Mosely v. Lake County – MT supreme court, January 12, 1993• Justice Court did not have jurisdiction to order fine over $1000
Current Fishery in LMR
???
Evidence: Born in LMR?
Distance from otolith core (UM)
87Sr/8
6 Sr
Evidence: Born in LMR?
Distance from otolith core (UM)
87Sr/8
6 Sr
2011Age = 1
2014: Administrative Rule on illegal fish introductions
2015: Following discovery of walleye in Swan Lake - 8 sporting groups pledge additional $5K to this reward
2016: Trout Unlimited offers $10K reward for convictions in select bull trout waters
Implications• More information about illegal introduction ‐> higher chance of conviction ‐30K reward
• New tool available to fisheries managers in the future
• Build Sr signature map to quickly identify sources
How you can help
• Be on the watch for suspicious activity
• Report observed illegal fish introductions 1‐800‐TIP‐MONT
• Identify species when angling
Acknowledgements
• Region 1 Fisheries personnel that provided the 2 walleye otoliths – Mark Deleray, Leo Rosenthal, Brian Marotz, and Matt Boyer
• Region 1 Law Enforcement that are working on the case
• Fisheries Biologist in MT that provided 3 Walleye otoliths from lakes and reservoirs ‐ Eric Roberts, Dave Yerk, Mike Ruggles, Cody Nagel, and Ben Bailer
• Geochemical analysis – WHOI Plasma Mass Spectrometry Laboratory Jurek Blusztajn
Questions
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