Sample Methods

· Lecture Outline

· Passive capture techniques

· Active capture techniques

· Sampling with toxicants

· Assignments

· pp. 221 – 254 and 384 – 432 in Fisheries Techniques

Passive Capture Techniques

1) Capture fish by devices that are not actively moved by humans or machines

2) Entanglement

3) Entrapment

4) Angling gears

Gill nets

1) Experimental gill nets

2) Mono- vs. Multifilament

Mono- versus multi- filament gill nets

Species effectively captured by gill nets

1) Fusiform fishes such as northern pike, walleye, yellow perch, trout, salmon, etc.

2) Fish with spines; particularly serrated spines

3) Some species (e.g., largemouth bass) avoid gill nets

Considerations for use of gill nets

1) Gill nets can cause substantial mortality

a) Short-term sets can alleviate problem

b) Sampling using gill nets is still justified

2) Size selectivity

a) Mesh size can determine size of fish captured

b) Probability of capture depends on fish encountering the net

i) Larger fish travel greater distances

c) Selection curves

Relative selectivity curves

Trammel net

1) Three mesh panels

a) Two outer, large-mesh panels

b) One middle, small mesh

c) Fish get caught in “bag”

2) Commonly used in commercial fisheries

3) Target species: ictalurids, catostomids, common carp, etc.

Passive entrapment gear (Hoop net)

1) Often used in flowing waters and with bait

2) Species often captured in hoop nets

a) Ictalurids (esp. Flathead catfish)

b) Catostomids (suckers)

c) Centrarchids (crappies and sunfishes)

Passive entrapment gear (Fyke net)

1) Most effective on species that seek cover (e.g., crappies and sunfish)

2) Often effective for collection of fish during spawning runs (e.g., walleye, kokanee salmon, northern pike)

3) Largemouth bass avoid traps

Passive entrapment gear (Pot gears)

1) Lobster, eel, and crap pots

2) Construction of wood, metal or plastic

3) Equipped with funnels to prevent escape

4) Used for bottom-dwelling or cavity seeking species

5) Commonly baited

6) Often fished in large numbers

Advantages of passive gear

1) Simple design and construction

2) Relatively low cost

3) Require little specialized training

4) Provide relatively precise data for standard samples

5) Some methods allow release of fish unharmed

Disadvantages of passive gear

1) Rely on fish activity

2) May damage bycatch

3) Partially selective for species, size, sex, etc…

4) Easy target for derelicts

5) Catch rates (CPUE) influenced by:

a) Environmental factors (season, temp. turbidity, currents)

b) Fish behavior

c) Morphology (shape, spines, etc…)

Active capture gear

1) Human or mechanical action moves gear to fish

2) Dragged or towed gears

3) Surrounding or encircling nets

4) Angling

Midwater trawls

Tucker Trawl

Bottom trawls

Purse seine

Pop nets

1) Effectively sample dense aquatic vegetation

2) Measure distribution, diversity and abundance

3) Sampling efficiency high (90 – 100%)

4) Large fish can escape more easily

Common sense seines

Snorkel surveys

Angling

1) Angling CPUE can be positively associated with electrofishing CPUE

2) Works for mark-recapture studies

3) Can be useful for food habits and telemetry studies

Toxicants

Rotenone

1) Natural substance from stems and roots of tropical plants (e.g., Jewel Vine, Flame tree, Lacepod, or Hoary pea)

2) Blocks transfer of electrons in mitochondria during cellular respiration

3) Detoxify with 1:1 addition of potassium permaganate (oxidizing agent)

4) Fish differ in their tolerance to rotenone

5) When to treat?

a) Between 50^o and 75^o F

b) Shorter retention time in warm months

6) How much?

a) 0.5 ppm to 5 ppm (usually 2ppm)

7) Side effects?

a) Zooplankton and some macroinvertebrates

b) No effect on snails, clams, and crayfish

Antimyacin

1) Antibiotic produced from mold

2) Blocks transfer of electrons in mitochondria during cellular respiration

3) Concentrations typically 5-10 :g/L (range 1 to 120 :g/L)

4) Oxidizes faster than rotenone (potassium permanganate)

a) Complete breakdown occurs within 1 to 14 days

5) Fish do not sense antimyacin

6) Typical uses

a) Catfish farmers use to remove scaled fish

b) Agencies use to restore native trout species in streams