Passive Fish Capture

Fishery sampling gears generally categorized as active or passive; However, toxicants 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. 0 2,000 4,000 6,000 8,000 10,00012,000 20 40 60 80 100 120 Population density

General disadvantages of passive gear: -- rely on fish activity -- 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 Examples: 6 panels -- 0.5, 0.75, 1.0, 1.5, 2.0, 2.5 in (bar measure)

stretch mesh (2X) }bar mesh

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

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

Seasonal changes in CPUE - Fish behavior (e.g., spawning) - Often highest in spring/fall and lower in summer 3 4 5 6 7 8 MAY JUN JUL AUG SEP OCT

Considerations: • 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

Trammel net Typically constructed of three mesh panels. The two outer panels have large mesh, and the middle panel is small mesh. Thus, the fish get caught in a “bag.”

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

Experimental Gill Net Case Study

Figure 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.

Passive entrapment gear • Entrapment: fish typically retained by some type of “funnel” • Trap (modified fyke) nets, and • Hoop nets most commonly used

Species 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

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

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