Passive Fish Capture

Collection Methods All are biased!

Fishery sampling gears generally categorized as active or passive; Toxicants (poisons) and electrofishing don’t fit these categories well.

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

If a gear is efficient for a species, then CPUE (catch-per-unit-effort) should be directly proportional to the abundance of fish in the populations. Thus, CPUE is an INDEX to abundance. Catch per day Population size of fish

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)

Most common example probably is the gill net

“Experimental” gill net has multiple panels of various mesh sizes Example: 6 panels , 0.75, 1.0, 1.5, 2.0, 2.5 in (bar measure)

Monofilament vs. multifilament Monofilament gill nets typically catch more fish Size structure similar between net types for most species Monofilament nets easier to run

Experimental Gill Net Catch

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

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

Trammel Net Typically 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.”

Trammel nets Commonly used in commercial fisheries Target species: catfishes, catostomids, Common Carp.

Passive Entrapment Gear Entrapment: fish typically retained by some type of “funnel” Trap (modified fyke) nets and hoop nets most commonly used

Minnow Trap

Fyke Net

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

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

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

Ghost Fishing