Spatial dynamics of the pelagic communities of Georgian Bay and Lake Simcoe
Erin S. Dunlop Aquatic Research and Monitoring Section, Ontario Ministry of Natural Resources and Forestry Why Study Pelagic Fish?
• Pelagic fish species are often the most abundant fish in a lake • Pelagic prey fish are an important food source for top predators • Highly dynamic in time and space (boom and bust cycles, variable year class strength) • Traditional assessment programs don’t sample the pelagic zone well Monitoring Programs
• Lake Huron – Ontario Ministry of Natural Resources and Forestry (OMNRF): benthic large‐mesh gill netting – USGS: (1) Benthic trawl surveys; (2) Pelagic trawl and acoustic surveys • Lake Simcoe: Benthic large mesh gill netting; creel surveys OMNRF Index Netting Locations
Upper Great Lakes Management Unit USGS Pelagic Surveys Project Objective: Evaluate the status of the pelagic community in 3 embayments of Georgian Bay and Lake Simcoe Background: Lake Huron
Alewife abundance
USGS Bottom Trawl Surveys
Riley et al. 2008; TAFS Simcoe Cisco Harvest
‐>Lake Simcoe Fisheries Assessment Unit Background
• Parry Sound – Lake trout showing positive signs of recovery ‐> natural reproduction • Severn Sound: poorer water quality; commercial fishing • Lake Simcoe – Collapsed cold water fish community now showing signs of recovery Pelagic surveys have not been conducted in these regions before Fisheries Acoustics
Strength of the returning signal provides information on density and size of targets in the water column
Surface Fish Schools
Individual Fish (single targets)
Zooplankton Range (depth) Lake Bottom
Time (or “ping”) ACOUSTICS SURVEYS 120 kHz 333 kHz
38 kHz 38 kHz 120 kHz 333 kHz
• Examine multiple components of the food web simultaneously Ecosystem‐based Approach • Examining the difference in the acoustic response of a species to different frequencies may aid in species identification Lake Simcoe Surveys Georgian Bay Surveys Parry Sound Transects (last week of July 2014) Severn Sound Transects (first week of August 2014) Simcoe Transects (first week of September 2014) NETTING Pelagic Trawl Pelagic Gill Netting
• modified “broadscale” net • 2 types: small and large mesh • 6 m height X 25 m long RESULTS: NETTING goby spottail, alewife ninespine cisco, perch, goby cisco smelt
smelt Severn Sound Parry Sound (757) (722) cisco TRAWL smelt CATCHES goby whitefish
emerald Simcoe (289) smelt cisco alewife GILL NET CATCHES
Severn sound small mesh: all smelt Severn sound large mesh: all cisco Parry Sound small mesh (380) lake trout emerald cisco cisco
whitefish
perch Simcoe Simcoe small mesh (411)large mesh (45) Parry Sound Alewife Species in the Pelagic Zone
• Parry Sound: smelt, alewife, cisco • Severn Sound: mainly smelt, a few cisco • Simcoe: cisco, shiner, a few smelt RESULTS: ACOUSTICS Fish densities from 120 kHz Target strength from 120 kHz Love’s multi‐species model Fish densities from 120 kHz Target strength from 120 kHz Love’s multi‐species model Fish densities from 120 kHz
Parry Sound Trawl Not all cisco sampled yet
Parry Sound Acoustics Target strength distribution Love’s multi‐species model Conclusions
• There were differences between locations • Lake Simcoe – Higher densities at surface (boat avoidance) and in hypolimnion Still have lots to learn about • Parry Sound spatial patterns of the pelagic – Most spatial variability communities of Lake Huron – Larger targets in hypolimnion – Alewife* • Severn Sound: least variation spatially and in species composition Acknowledgments
• Field support (OMNR) – Aquatic Research Section: Michael Pinder, Ben Maynard, Jeremy Metzger, Justin Trumpickas, Katie Gillespie, Nathan Staels, Derek Lipskie – Upper Great Lakes Management Unit: John Brookham and Brandon MacLean – Lake Simcoe Fisheries Assessment Unit (Todd Langley, Jake LaRose) • Data support (OMNRF) – Justin Trumpickas and Issac Hebert • Acoustic technical assistance: Scott Milne • Funding: Lake Simcoe Southeastern Georgian Bay Clean‐up Fund (Environment Canada) and Lake Simcoe Protection Plan