2Fishery sampling gears generally categorized as active or passive; However, toxicants and electrofishing don’t fit these categories well.
3Passive entanglement gear • Passive: gear is relatively stationary,and fish come to gear• Entanglement: they get tangled
4General advantages of passive gear: -- simple design and construction-- relatively low cost-- require little specialized training
5If a gear is efficient for a species, then CPUE (catch-per-unit-effort) should be directly proportional tothe abundance of fish in the populations. Thus CPUE is an INDEX to abundance.0 2,000 4,000 6,000 8,000 10,00012,00020406080100120Population density
6General disadvantages of passive gear: -- rely on fish activity-- may damage bycatch-- can be selective for species, size,sex... (more on this later)
10Monofilament vs. multifilament • Monofilament gill nets typically catchmore fish• Size structure similar between net types for most species• Monofilament nets easier to run
11Species 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
12Seasonal changes in CPUE - Fish behavior (e.g., spawning)- Often highest in spring/fall andlower in summer345678MAY JUN JUL AUG SEP OCT
13Considerations:• Gill nets can cause substantial mortality• Short-term sets can alleviate some of problem• However, sampling can still be justified• Most biologists prefer to use most benign gear that is still effective
14Trammel netTypically constructed of three mesh panels.The two outer panels have large mesh, andthe middle panel is small mesh. Thus, thefish get caught in a “bag.”
15Trammel nets• Commonly used in commercial fisheries• Target species: catfishes, catostomids, Common Carp.
17Figure 1. Length frequency for a sample of yellow perch (YEP) collected with experimental gill nets from a natural lake in the northern United States during the spring. All length measurements were maximum total length.
18Passive entrapment gear • Entrapment: fish typically retained by some type of “funnel”• Trap (modified fyke) nets, and• Hoop nets most commonly used
22Species effectively captured: 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
23Species effectively captured by hoop nets • Often used in flowing waters; often baited• Catfishes• Suckers: buffalo fishes, carpsuckers• Crappies and sunfishes
24Considerations• Both trap and hoop nets inflict little mortality; most fishes can be released alive
25Pot 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