Trends from 21 Years of Lake Sturgeon Assessments in the St. Clair - - PowerPoint PPT Presentation

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

200 400 600 800 1000 1200 1400 1600 1800 2000 1995 2000 2005 2010 2015 TL (mm)

Setline Size Distribution Trends

Trawl Size Distribution Trends

200 400 600 800 1000 1200 1400 1600 1800 2000 1995 2000 2005 2010 2015 TL (mm)

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