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

Pelagic

Bottom

Freshwater Equivalent=

Passive GearEntrapment- trap nets, know the parts!

Wings

Wings

Lead

Pot or Car

Funnel

Considerations: location, mesh size, funnel diameter

Trap nets, Lots of variety

Pound NetFyke Net

PA style trap Net

Hoop Net - river

River Trap Net

Block entire stream, catch everything going up or down

Passive Gear – Fish Weirs

Considerations: location, high level of effort, non-target effects

Passive GearMinnow trap – can mean anything

Glass style

square

B style

Plastic style

Gee style

Considerations: location, mesh size, funnel diameter, trap fullness = more or less caught, predation

Passive GearAngling – 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

Rockhopper

Tickler chains

Active gear Drag/Tow – larval fish sampling – Bongo nets, Miller sampler

Reduced Opening

Standing Wave

Considerations: depth, size of larvae, other stuff in water

Active gear - SeinePurse seine and beach seine

Considerations: how to find fish, preventing escape, bycatch

Active gear - ElectrofishingStream electrofishing- backpack, 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 windowsConsiderations: behavioral changes

due to your presence, water clarity, can’t measure some things

Active gear - hydroacousticsConsiderations: 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!

25 A25 B25 C25 D

A B C D5 6 5 7

A B C D20 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!