Lecture 2.3 Sampling Fish and Wildlife Populations

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Lecture 2.3Sampling Fish andWildlife Populations

• Natural Resources 250
• Michael J. Hansen
• Professor of Fisheries

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Outline

• Sampling.
• Passive capture methods.
• Active capture methods.
• Electrofishing.
• Anesthetics.
• Toxicants.
• Traps, sieves, and dredges.
• Indirect methods.

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Sampling

• Sample is a portion of a population.
• Sample must be representative.
• Capture methods are all biased.
• Capture process affects sampled organisms.
• Sampling method may be lethal.
• Sampling method may alter behavior.
• Sampling methods can be complimentary.

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Passive Methods

• Entanglement devices.
• Fish gill nets and trammel nets.
• Birds mist nets and drive nets.
• Mammals leg-hold traps and snares.
• Entrapment devices.
• Fish hoop and trap nets.
• Mammals funnel traps and box traps.

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Passive MethodsEntanglement Devices - Fish

• Floats and leads stretch net vertically.
• Anchors keep net positioned in space.
• Gill nets wedge and entangle fish.
• Mesh size targets particular size of fish.
• Multiple mesh sizes are needed to better
  represent the entire range of fish sizes.
• Trammel nets surround fish in fine mesh.

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Passive MethodsEntanglement Devices - Birds

• Nets suspended between poles or trees.
• Birds (and mammals) driven into nets.
• Birds (and mammals) are entangled.

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Passive MethodsEntanglement Devices - Mammals

• Leg-hold traps snap onto leg of mammals.
• Snap traps kill target animal.
• Snares encircle neck of body of mammal.
• Demonstrate traps at front of room!

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Passive MethodsEntrapment Devices - Fish

• Nets have series of hearts.
• Fish cannot exit a heart once entered.
• Continue into cod end of net.

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Passive MethodsEntrapment Devices - Mammals

• Funnel traps lead into central holding area.
• Box traps close entry way when tripped.
• Pit traps collapse downward.

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Active Capture MethodsFish Sampling

• Seines are used to encircle fish.
• Trawls are towed to capture fish.
• Dredges are towed to capture shellfish.

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Active Capture MethodsWildlife Sampling

• Cannon nets are launched over wildlife.
• Drop nets are dropped onto wildlife.

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Electrofishing

• Electrical current immobilizes fish.
• Excessive current kills fish or damages fish.
• Alternating current (AC) stuns fish in place.
• Direct current (DC) draws fish into field.
• Many factors affect effectiveness.

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Anesthetics

• Dart guns immobilize wildlife for study.
• Drugs immobilize fish after capture by other
  methods.

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Toxicants

• Rotenone and antimycin (general use).
• Rotenone blocks oxygen uptake at gills.
• Antimycin blocks cellular uptake of oxygen.
• Toxicity affected by many factors.
• TFM and Bayer-73 (sea lamprey).
• Selective for lampreys, amphibians, etc.
• TFM is dissolved in water.
• Bayer-73 adsorbed to sand.

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Traps, Sieves and Dredges

• Plankton, fish eggs, and fish larvae.
• Benthic organisms in lakes.
• Benthic organisms in streams.

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Indirect Methods

• Count songs of breeding birds.
• Count eyes of mammals in spotlights.
• Count feces of mammals.
• Count echoes of fish (hydroacoustics).

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