Environmental Factors and Fish Ecology

Environmental factors affecting organisms and local assemblages•Many factors•High complexity•Abiotic

•Large, long•Geological strata•Climate change

•Small, short•Micro-hydraulics•Temperature

•Biotic•Competition•Predation

From Matthews 1998

Important Abiotic Environmental Variables Affecting Organisms in Streams

• Current velocity/Discharge• Substrate• Temperature• Dissolved oxygen

Relationships between environmental variables can be very important

Organism Adaptations to Flow

• Streamlined shape– Fusiform shape

– Reduced fins and fin location

• Suckers• Benthic habit

– Enlarged pectoral fins

– Dorsal eyes

– Loss of swim bladder

Effect of Current Velocity and Discharge on Substrate

Effect of Current Velocity on Fish

• Position maintenance– Swimming ability

• Species, size, life stage– Energy use

• Food availability– Drift feeders

• Bioenergetically– Cost/benefit relationship

Hill and Grossman 1993

Effect of Substrate on Current Velocity and Flow

• Eddies• Wake interference• Quasi-smooth flow

Ozark Highlands•Lower gradient•Cobble-gravel•Spring influence

Boston Mountains•Higher gradient•Bedrock-cobble•High flow variation

Research Questions

• Does fish morphology predict fish swimming ability and refuge use?

Central stoneroller Campostoma anomalum

Cardinal shiner Notropis cardinalis

Orangethroat darter Etheostoma spectabile

Green sunfish Lepomis cyanellus

Longear sunfish Lepomis megalotis

Pictures by W. N. Roston, from ‘Fishes of Arkansas’

Five Common Arkansas Stream Fish

Two substrate types:

1. Complex (w/ rocks)

2. Smooth plexiglas

Velocity increased by

10 cm/s every 15 min

until fish exhaustion

ResultsMean CSS in cm/sec (SE)

Low complexity High complexity

Central stoneroller 35.51 (2.52) 37.40 (8.40)

Cardinal shiner 31.70 (2.38) 26.48 (4.59)

Orangethroat darter 22.49 (3.02) 17.25 (4.49)

Longear sunfish 14.40 (0.18) 15.74 (3.67)

Green sunfish 13.89 (0.59) 11.41 (5.77)

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Temperature• Mean, max and min

temps.– Survival– Growth– Reproduction

• Cumulative temperature– Degree-days– Latitude– Stream size– Groundwater influence– Elevation

Effect of Temperature on Egg Hatching

Temp and DO in Lakes and Rivers

Allan 1995

Organisms Vary With Abiotic Variables

Longitudinal pattern in streams• Rivers generally increase in size as one proceeds

downstream– Velocity (U) varies with gradient, depth, and substrate texture

• Average velocity usually increases downstream!– Gradient decreases, but depth increases and friction

decreases

Gradient

Friction

Depth

Velocity

Distance from headwater

Fish species and numbers are related to these changes in stream abiotic variables.

Size (Spatial and Temporal Scale) Matters

• Relationship between environmental variables and organisms is scale dependent

Questions

• How do crayfish species-environmental relationships change with spatial scale?

• How do lotic crayfish species relationships change with spatial scale?

Study Design

S amplen=56 7

Runn=18 9

S t ream S ect ionn=6 3

S t reamn=21

S ub-wat ershedn=7• Balanced,

hierarchical design.

• Replicate units contained within a particular level.

• Each level represents a different level of spatial scale.

Study Site• Drainage area of

3, 926 km2

• Streams 2nd or 3rd order.

• Stream sections at least 500 m apart defined as 3 consecutive runs separated by riffle or pool habitats.

Spring RiverWatershed

Field Methods

• Measurements of substrate composition, stream width, current velocity, and depth measured at each sample location.

• Water temperature, pH, and conductivity measured in each stream section.

• Crayfish collected identified to species, sexed, and carapace length measured.

Contribution to Species-Environment Relationships

Effect Variance % explainedSub-watershed 0.033 27.0

Stream 0.029 23.8

Stream section 0.026 21.3

Run 0.018 14.8

Sample 0.016 13.1

TSS 0.122

Variable Watershed Stream StreamSection

% Cobble ** ** *Depth ** N. S. *% Pebble ** N. S. N. S.Conductivity ** N. S. N. S.Temperature ** * N. S.Width ** ** N. S.pH * N. S. N. S.% Gravel N. S. ** **% Boulder N. S. N. S. N. S.Velocity N. S. N. S. N. S.% Bedrock N. S. N. S. N. S.

Importance of Environmental Variables with Scale

** < 0.005 * < 0.05 N. S. = Not Significant

Contribution to Crayfish Species Relationships

Effect SS % varianceexplained

F p

Sub-watershed 0.189 18.9 21.7 0.002Stream 0.123 12.3 6.95 0.002Stream section 0.158 15.8 3.59 0.002Run 0.195 19.5 1.74 0.005Sample (RSS) 0.335 33.5 - -

TSS 1.00

Conclusions• Importance of environmental variables differed

among levels of scale.• Largest scale (sub-watersheds) explained most

variation in species-environmental relationships (27.0%) and this decreased with decreasing spatial scale.

• Greatest amount of variation in crayfish species relationships explained (33.5%) attributed to differences at the microhabitat (sample) level.