Trends from 21 Years of Lake Sturgeon Assessments in the St. Clair System Andrew S. Briggs, Jan-Michael Hessenauer, Brad Utrup, and Michael V. Thomas
Pre-1996 • Little known about Lake Sturgeon Populations in the SCDRS • Recreational fishery was present but unmonitored • No targeted assessments • Statewide Rehabilitation Plan in development – Information gaps identified
MDNR Lake Sturgeon Study • Began in 1996 • Purpose: – Annually document status and dynamics – Aid in conservation and sound management
Primary Survey Techniques Setlines Trawling
Primary Survey Techniques
Data Collection • Length, weight, and girth • Sex and maturity • Fin ray for aging (TL < 1,016 mm) • Lamprey scars • Abnormalities • Tag (PIT and Monel)
Recreational Fishery Monitoring • Regulations – Fishing season July 16 to Nov. 30; possession season July 16 to Sept. 30 – 1 fish per year; 1,067 to 1,270 mm harvest slot limit – Harvested fish must be registered (online or toll free phone-in) • Sturgeon patch
Outline • General catch info • Tag retention • Catch trends – Overall catch rates – Size distribution – Juvenile catch rates • Trends in recreational fishery – Fishing effort – Harvest • Future plans
General Catch Info • 3,219 total tagged Lake Sturgeon • 244 – 1,887 mm TL • Targeted catch – Setlines: 2,481 – Sturgeon trawls: 934 • 727 recaptures of 481 unique Lake Sturgeon (14.9%)
Length Frequency
Tag Retention • Our tagging methods – Monel tagging since 1996 • Base of dorsal fin • >762 mm: 2006 - 2009 • >914 or 965 mm: 2010 - 2014 • >1,016 mm: 2015 - present – PIT tagging since 2001 • Under dorsal scute • Analysis of retention only includes fish originally tagged from 2001 – present • Tag was assumed lost during the year the fish was recaptured without the tag
Monel Tag Retention Years at Large Total Tags Tags Retained Retention Rate 1 178 174 97.8% 2 142 142 100.0% 3 114 113 99.1% 4 89 86 96.6% 5 65 62 95.4% 6 50 49 98.0% 7 39 39 100.0% 8 35 34 97.1% 9 25 22 88.0% 10 19 17 89.5% 11 12 12 100.0% 12 5 4 80.0% 13 3 2 66.7% 14 1 1 100.0% 15 1 1 100.0%
PIT Tag Retention Years at Large Total Tags Tags Retained Retention Rate 1 176 176 100.0% 2 142 142 100.0% 3 117 117 100.0% 4 91 91 100.0% 5 67 67 100.0% 6 54 54 100.0% 7 44 44 100.0% 8 38 38 100.0% 9 28 28 100.0% 10 23 23 100.0% 11 15 15 100.0% 12 5 5 100.0% 13 3 3 100.0% 14 2 2 100.0% 15 2 1 50.0%
Catch Rates
Trawl Catch Rate and Secchi Depth
Trawl Catch Rate vs. Secchi Depth
Setline Size Distribution Trends 2000 1800 1600 1400 1200 TL (mm) 1000 800 600 400 200 0 1995 2000 2005 2010 2015
Setline Size Distribution Trends
Trawl Size Distribution Trends 2000 1800 1600 1400 1200 TL (mm) 1000 800 600 400 200 0 1995 2000 2005 2010 2015
Trawl Size Distribution Trends
Recreational Fishery • 206 angler recaptures through 2017 • 109 Lake Sturgeon harvested since 1999 (5.7/year) • Anecdotal evidence of increased fishing pressure (Sturgeon for Tomorrow) – More anglers on a given night – More Charters targeting Lake Sturgeon • Data?
Angler Recapture Rate
Angler Harvest • 50 harvestable, tagged sturgeon have been caught with 8 being harvested (16%)
Summary • PIT and Monel tag retention high – PIT higher (nearly 100%) – Issues with Monel tags at smaller sizes • Setline catch is steady, while trawl catch has declined • More juveniles being caught on setlines recently • Predominantly adults being caught in trawls • Increasing angler effort
Future Plans “Keep on keepin ’ on!” • Continue setline and trawl surveys • Be adaptive • Continue collaborative spirit …and more!!
Questions Andrew S. Briggs BriggsA4@michigan.gov @FishBio_Briggs
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