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Chapter 6

Chapter 6. Passive Capture Techniques. Passive Capture Techniques. Fish caught by Entanglement Entrapment Angling gears Gear is not moved through the water. Entangling devices. Fish are snared or tangled in fabric or mesh Examples Gill nets Trammel nets. Entrapment devices.

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Chapter 6

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  1. Chapter 6 Passive Capture Techniques

  2. Passive Capture Techniques • Fish caught by • Entanglement • Entrapment • Angling gears • Gear is not moved through the water

  3. Entangling devices • Fish are snared or tangled in fabric or mesh • Examples • Gill nets • Trammel nets

  4. Entrapment devices • Capture fish that go through small openings in gear • May be more than one opening • Fish can't find their way out • Examples • Hoop nets • Trap Nets • Lobster Pots

  5. Angling devices • Use baited hooks on lines • May be unattended • Examples • Trot lines • Long lines • Jugs and yo-yos

  6. Problems with passive gear • Gear selectivity - bias for or against certain species, sizes or sexes of fish. • Example - trap nets catch crappie, but usually not largemouth bass orr X

  7. Problems with passive gear • Gear efficiency - number of target animals collected for a given amount of effort expended • Example - gill nets catch fewer crappie per net night than trap nets

  8. Advantages of Passive Gear • Simple design and construction • No mechanical assistance (except boat) • Same gear each year ... CPE ~ = Population Abundance

  9. Disadvantages of Passive Gear • Gear selectivity influences • Encounter • Caught • Retained

  10. Capture efficiency influences • Season • Turbidity • Current • Time of day • Water Temperature

  11. Other Considerations • Animal Behavior • Movement • Schooling • Fish morphology See Fish Swim Swim Fish Swim

  12. Gill Nets - Fish caught by... • Wedged • Gilled • Tangled

  13. Gill Nets - Construction • Hanging Ratio • Mesh size (Bar or stretch) • Wall of Netting • Floats, Weights • Anchors, Bouys

  14. Net Cotton Linen Nylon Monofilament Floats Wood Cork Plastic Lead weights on bottom Gill Nets - Materials

  15. Gill Nets - Set Procedure • Deployment • Drop anchor, play out untangled net, drop anchor • Retrieval • Start from downwind, remove fish, into tub in coils

  16. Gill Nets - Types of Sets • Standard - anchored on bottom like a fence • Midwater - suspended mid-depth by lines • Surface - strong floats • Vertical - for determining vertical distribution (windowshade) • Drift - not anchored

  17. Gill Nets - Biases (cont.) • Mesh size, elasticity, hanging ratio, strength, visibility • Movement of fish • Duration (soak-time)

  18. Gill Nets - Biases • Optimal girth . . . 1.25 x mesh perimeter • Few smaller or larger fish than optimal =1.25 x

  19. Season Weather fronts Currents Water temperature Movement of Fish

  20. Water depth Thermocline location Movement of Fish • Fluctuations in water level • Turbidity

  21. Trammel Nets - Construction (cont.) • Three panels of netting • small mesh sandwiched between two large mesh • Float line • Lead line • Fish in a pocket made of small mesh poked through large

  22. Trammel Nets - Material • Cotton or nylon • 2-m deep • 250-mm bar • 25-mm bar

  23. Same as gill nets Standard sets Floating sets Trammel Nets - Sets • Common in commercial fisheries

  24. Hoop Nets - Construction • Cylindrical or conical • Frames covered by mesh • Square or finger throat • Cod end • Anchor • Bouys

  25. Hoop Nets - Material • Hoops - wood, plastic, fiberglass, steel • 0.5 to 3m diameter • Cotton or nylon mesh • 10 to 100mm bar mesh

  26. Hoop Nets - Sets • Riverine habitats - good in strong currents • Anchor upstream, stretch out, mouth downstream • Baits - cheese, soybean cakes, chicken livers

  27. Hoop Nets - Biases • Hoop size • Mesh size • Escape rates • Season, temperature, current, turbidity, habitat type

  28. Fyke and Trap Nets - Construction • 1-3 wings or leaders (guide fish) • enclosure with throat • float • anchor

  29. Fyke and Trap Nets - Materials • Hoops or rectangular frames - metal • 0.5 to 2m diameter • Cotton or nylon mesh • 10 to 100mm bar mesh

  30. Fyke and Trap Nets - Sets • Lakes and reservoirs • Perpendicular to shore • Leader onshore, anchor away • Floating trap nets

  31. Fyke and Trap Nets - Biases • Species and size selectivity - good for crappie • Live releases - mostly larger sport fish

  32. Pot Gears - Construction • Rigid traps with throats • Widely variable for different species • Box or cylinder with conical funnel • Usually with door for easy removal

  33. Pot Gears - Materials • Plastic • Wood • Metal • Partial mesh

  34. Pot Gears - Sets • Usually over the side of boat, with float attached • Suspended in midwater - minnow traps

  35. Pot Gears - Biases • Same as other gear • Ghost fishing • Overcrowded traps

  36. Angling Gear • Trot lines • Floats, lines, drop hooks, weights • Mostly warm water inland fisheries

  37. Angling Gear • Long lines • Floats, lines drop hooks • Mostly oceanic fisheries (miles/longline)

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