Coldwater Fisheries

• Lecture Outline

• Assignments

Coldwater Fishes

1) Anadromous fishes

a) Immediately disperse to sea

b) Remain in streams before migrating to sea

2) Resident fishes

Distributions

Temperature and Dissolved Oxygen

1) Summer temperature generally 22 ^oC or less

2) Optimum growth occurs at 15 to 20 ^oC

3) DO should be 8 – 10 mg/l

4) Over-winter mortality can be high

a) Anchor ice

b) Movement to thermal refuges

c) Concealment in substrate

Habitat Constraints on Salmonids

1) Four habitats required for various stages of life (Benke 1992)

a) Spawning – Gravel necessary to build redds

b) Nursery or rearing – Low velocity off-channel habitats

c) Adult – Deep pools with overhanging structure

d) Overwintering – Deep water with low current velocity and protective cover

Reproduction

1) Western trout evolved to spawn in spring with rising temperature

a) Eggs develop in 300 degree-days

2) Brook and Brown trout spawn in Fall

a) 50 days….50 degrees F

3) Need flowing waters with low sediment loads

4) Fecundity ranges from 1,200 to 3,200 eggs per kilogram of body weight

5) Most fish spawn between age 2 – 4

Territoriality

1) Competition to establish feeding territory

2) Nipping and chasing

3) Threat postures and body shading

4) Species can easily be displaced by introductions

Movements

1) Knowledge of fish movement is essential to management of fishes

2) Restricted Movement Paradigm (Gerking 1959)

a) Most fish spend majority of life is one pool or stream reach

3) Restricted Movement Paradigm largely based on inability to capture marked fish large distances from where they were tagged (Gowan et al. 1994)

Flow regime

1) Life history of salmonids adapted to a particular flow regime

Sedimentation

1) Sedimentation is detrimental to production of salmonids

2) Clean cobbles needed for:

a) Production of invertebrates

b) Spawning habitat

Allan Paradox

1) Fish require many times more benthic prey than are available at any instant in time

2) Benthic invertebrates 4 – 120 g m-2 yr-1

3) Salmonids 11 – 300 g m-2 yr-1

4) Possibly explained by:

a) Supplement of terrestrial arthropods

b) Recruitment from hyporheic fauna

Management

1) Stocking

a) Necessary when natural production is low

b) Average cost per adult trout $1.50

c) Competition with naturally producing fish

d) Response depends on number of fish stocked and angling pressure

2) Habitat Improvement

a) More emphasis on watershed management

b) Riparian enhancement

c) Large woody debris important

3) Harvest regulations

a) Catch and release

b) Gear restrictions

c) Delayed harvest

4) Angler surveys