Fish Sampling Methods

Question 1

Why do we do fish inventories? (3)

Answer 1

To identify all fish species in all habitats
To predict contributions to commercial and recreational fisheries
To predict escapement (how many will spawn)

Question 2

Where and how do we do fish inventory? (2)

Answer 2

Using passive gear (e.g. fences, floating traps installed in the lower watershed)

Using active gear (e.g. electrofishing, pole seining etc. used upstream in smaller tributaries)

Question 3

What are the factors that affect gear selection? (5)

Answer 3

Water depth 
Bed characteristics
Vegetative cover 
Target species 
Season and flow regime

Question 4

What is Gear Selectivity and Gear Efficiency? (2)

Answer 4

Gear selectivity is the bias of a sample obtained with a certain gear type when gear over-represents certain species, sizes, or sexes of fish

Gear efficiency refers to the amount of effort needed to capture target organisms - generally for time and financial reasons we want to select gear to maximize efficiency

Question 5

What is passive gear? (4)

Answer 5

Depends on the movement of fish into the gear, not actively moved by human or machine effort

Relatively simple in design and use

Appropriate for fish capture during migrations and periods of movement

Useful in habitats where more active methods would be impeded by underwater obstacles or vegetation

Question 6

What are the three groups of passive gear? (3)

Answer 6

Entanglement (e.g. gill nets)
Entrapment (e.g. minnow traps or hoop nets)
Angling gears (e.g. long lines)

Question 7

What are the main types of passive gear we went over? (7)

Answer 7

Gill nets 
Hoop/fyke nets 
Minnow (Gee) traps
Fish counting fences/weirs
Fish wheels
Inclined Plane Traps
Rotary screw traps

Question 8

What are gill nets? (4)

Answer 8

Vertical panel of netting maintained by a float line and a lead line

Can be set at varying water depths

Highly selective for different sizes of fish depending on the mesh size

Generally is a lethal sampling event

Question 9

What are the 3 ways that fish can get caught in a gill net?

Answer 9

Wedged - fish is held by mesh around body
Gilled - fish is held by mesh slipping behind the opercula
Tangled - fish is held by teeth, spines, maxilliaries, or other protrusions without them body penetrating the mesh

Question 10

What are fish traps? (4)

Answer 10

Designed to encourage fish to enter a confined space and the. Percent the fish from leaving the chamber once they have entered

Can be baited or unbaited

Often highly size selective for smaller fish but can catch any size that can pass through the entrance

E.g. minnow traps or hoop nets

Question 11

What are hoop/fyke nets? (4)

Answer 11

Catch a portion of the out-migration
May use panels to deflect fish into the long net or sock
Net must be attended to daily
Fyke nets consist of a cylinder supported by hoops within which cones of netting act as a non-return valve. Deflections include wings and leads that direct fish into the fyke net

Question 12

What are minnow (Gee) traps? (5)

Answer 12

Effective method of capturing fish in habitats that do not have sufficient water velocities to employ other trap types

Should be installed in quiet back water areas such as pools and back eddies

Maximum recommended soak time is 24 hours

Traps are often set with bait and places with opening facing upstream

Small fish enter through opening and once inside it is used to escape

Question 13

What are fish counting fences/weirs? (4)

Answer 13

Capture 100% of out or in - migration

Inexpensive, easy to build and install

Require frequent maintenance and cleaning

Site selection is critical

Question 14

What are fish wheels? (2)

Answer 14

Wheel contraption that floats in flow of stream

Fish swim into it and are scooped up and put into holding area

Question 15

What are inclined plane traps?

Answer 15

An inclined aluminum plane is fixed in flow of stream and as fish swim up it, they unable to back up and end up in holding area

Question 16

What are rotary screw traps? (3)

Answer 16

Floating trap that captures out-migrating fry and smolts

Used to estimate fry and smolt abundance and timing

Water velocity turns the large drum with 5 to 8 rotations per minute

Question 17

What is active gear? (3)

Answer 17

Depend on the gear moving to capture fish by way of boat or human effort

Sampling efforts are generally mobile in space and time (unlike most passive gear sampling) and can be deployed for shorter periods of time

Most appropriate for capturing fish when they are relatively stationary at the bottom, in the water column, or in some kind of refuge

Question 18

What are the main types of active gear? (4)

Answer 18

Using seine nets for:

Stick (pole) seining
Kick seining
Beach seining

Question 19

What is a seine net? (4)

Answer 19

Consist of a sheet of netting attached to a head line with floats, a weighted foot line, as a bridle ropes for hauling

Usually set from shore in a semi-circle

Fish are disturbed as the net passed by and swim into the net

Can be used in both lakes and rivers

Question 20

What is stick (pole) seining? (4)

Answer 20

Used on smaller streams

1 and 2 person netting systems available

Operators move downstream in fast water, upstream in slower-moving water

Net is folded or purses following a pass, and lifted from the water column

Question 21

What is kick seining? (2)

Answer 21

Works well for fish species living in interstitial spaces in the cobbles

The bed material is disturbed and the fish flow into the net

Question 22

What is beach seining? (5)

Answer 22

Generally 10 to 30 meter long nets of uniform mesh size

Used to capture juveniles and adults

Typically used in shallow water where the bet wall extends from the surface to the bottom

Most effective in large, smooth bottom rivers and lakes, lead line must be in contact with the bottom to prevent fish from escaping

In fast water, set downstream and use a purse net around potential habitats