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Fisheries Techniques
Zoo 511
Today’s outline
• Announcements:
– Final Exam next week!
• Format will be one section with timed stations, and
one section with a total time limit for multiple
questions.
– Final Draft of paper due noon May 14th in
Alex’s mailbox at the CFL
• Lecture: Techniques (this is fair game for
exam!)
• Jeopardy!
Two main types of methods:
ACTIVE
PASSIVE
Passive Gear
Entanglement – gill nets
Considerations: habitat, depth, mesh
size, mortality
Standard
Nordi-mesh
Passive Gear
Entanglement -Longlining
Considerations: Habitat, by-catch, hook size,
type of bait, set time, predation, finding the
gear
Freshwater Equivalent=
Pelagic
Bottom
Passive Gear
Considerations: location,
mesh size, funnel diameter
Entrapment- trap nets, know the parts!
Wings
Pot or Car
Funnel
Wings
Lead
Trap nets, Lots of variety
Fyke Net
Pound Net
River Trap Net
PA style trap Net
Hoop Net - river
Passive Gear – Fish Weirs
Block entire stream, catch everything going up or down
Considerations: location, high level of effort, non-target effects
Passive Gear
Minnow trap – can mean anything
Considerations: location, mesh size, funnel
diameter, trap fullness = more or less caught,
predation
Gee style
B style
square
Glass style
Plastic style
Passive Gear
Angling – sort of a weird mix between active/passive
Considerations: time and place, what lure, certain types of fish more
vulnerable, behavioral effects
Active gear – Trawling
Considerations: depth,
bycatch, habitat destruction
Tickler
chains
Rockhopper
Active gear
Drag/Tow – larval fish sampling – Bongo nets, Miller sampler
Considerations: depth,
size of larvae, other stuff
in water
Reduced Opening
Standing Wave
Active gear - Seine
Purse seine and beach seine
Considerations: how to
find fish, preventing
escape, bycatch
Active gear - Electrofishing
Stream
electrofishingbackpack, tow
boat, bank based,
electric seine
Considerations: safety –
fish and researchers, not
effective in all habitats
Active gear Boat Electrofishing
Considerations: depth,
safety again
Active gear Toxicants – rotenone, lampricides
Considerations: Selectivity, ease of
application, health concerns
Active gear Direct observations (underwater,
camera, or viewing windows
Considerations: behavioral changes due
to your presence, water clarity, can’t
measure some things
Active gear - hydroacoustics
Considerations: expensive, how to
determine species composition, difficult
to sample fish near the bottom
Gear Bias
• Why certain species, sizes, or habitats are
caught more or less often than their
frequency in the population.
• Every gear has bias!
A B C D
5 6 5 7
25 A
25 B
25 C
25 D
A B C D
20 4 1 15
Gear Bias
• Gear can also be biased for size
• You sample and catch only one size of fish:
2 possible reasons.
– The population is all one size
– Your gear is biased towards one size
• Goal is to get least biased sample possible
• USE MULTIPLE GEARS!