passive fish capture. collection methods all are biased!
DESCRIPTION
Fishery sampling gears generally categorized as active or passive; Toxicants (poisons) and electrofishing don’t fit these categories well.TRANSCRIPT
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PassiveFishCapture
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Collection MethodsAll are biased!
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•Fishery sampling gears generally categorized as active or passive;
•Toxicants (poisons) and electrofishing don’t fit these categories well.
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Passive entanglement gear
• Passive: gear is relatively stationary,and fish come to gear• Entanglement: they get tangled
General advantages of passive gear:-- simple design and construction-- relatively low cost-- require little specialized training
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General disadvantages of passive gear:
-- rely on fish activity: if they are not moving, you won’t catch them
-- may damage bycatch
-- can be selective for species, size,sex... (more on this later)
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Most common example probably is the gill net
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“Experimental” gill net has multiplepanels of various mesh sizes
Example: 6 panels -- 0.5, 0.75, 1.0, 1.5, 2.0, 2.5 in (bar measure)
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Experimental Gill Net Catch
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Species effectively captured:• Gill nets most effective on fusiform (torpedo-shaped) fishes such as Northern Pike, Walleye, Yellow Perch, trout and salmon, etc.• Largemouth Bass avoid gill nets
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Considerations:
• Gill nets can cause substantial mortality
• Short-term sets can alleviate some of problem
• Most biologists prefer to use most benign gear that is still effective
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Trammel NetTypically constructed of three mesh panels:
• two outer panels have large mesh, and the middle panel is small mesh. Thus, thefish get caught in a “bag.”
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Trammel nets• Commonly used in commercial fisheries• Target species: catfishes, catostomids, Common Carp.
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Passive Entrapment Gear
• Entrapment: fish typically retained by some type of “funnel”
• Trap (modified fyke) nets and hoop nets most commonly used
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Minnow Trap
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Fyke Net
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Species effectively captured by trap nets:
• Most effective on species that seek cover, such as crappies and sunfishes• Often effective for collection of spawning Northern Pike or Walleye• Largemouth Bass avoid trap nets
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Species effectively captured by hoop nets• Often used in flowing waters; often baited• Catfishes• Suckers: buffalo fishes, carpsuckers• Crappies and sunfishes
Considerations• Both trap and hoop nets inflict little mortality; most fishes can be released alive
Bigmouth Buffalo Fish River Carpsucker
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Pot Gears
-e.g., lobster, eel & crab pots, fish traps
-construction of wood, metal or plastic
-equipped w/funnels to prevent escape
-used for bottom-dwelling or cavity-seeking spp.
-commonly baited
-often fished in large numbers
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Ghost Fishing