Ecological Archives A025-134-A3

Kimberly L. Dibble, Charles B. Yackulic, Theodore A. Kennedy, and Phaedra Budy. 2015. Flow management and fish density regulate salmonid recruitment and adult size in tailwaters across western North America. Ecological Applications 25:21682179. http://dx.doi.org/10.1890/14-2211.1

Appendix C. Description of hypotheses on the response of rainbow and brown trout recruitment and mean adult length to flow, biological, and other predictors.

Table C1. Hypotheses on the predicted response of rainbow trout (RBT) and brown trout (BT) recruitment and mean adult length to an increase in predictor variables. The predicted sign of the response may vary between rainbow and brown trout, as indicated by separate columns.

Response

Predictor

RBT Sign

BT Sign

Justification

Recruitment

Hydropeaking (variable subdaily flow, based on the coefficient of variation)

-

-

Redd de-watering decreases survival of eggs and newly emerged fry; decreases growth

 

Relative annual flow

+

+

Channel expands into low-velocity shelf habitats; energetic savings

 

Specific discharge

-

-

High velocity water is energetically costly; decreases survival and growth

 

1st axis, Principal Component Analysis (PC1; ↑ summer flow)

+

+

Channel expands into low-velocity shelf habitats; energetic savings; better prey availability

 

2nd axis, Principal Component Analysis (PC2; ↑ winter, ↓ spring flow)

+

-

Flow response increases egg and fry survival during the spawning season; decreases competition from competing species

 

Rainbow and brown trout catch (sub-adult, adult)

-

-

Interspecific competition for prey; adult BT prey on sub-adult RBT (competing species only included in model)

 

Fish stocking

-

-

Natural reproduction may not be sufficient to support population

 

Whirling disease

-

+

Disease disproportionally affects RBT (decreased survival relative to BT); BT are often disease-resistant and may increase in open niche

 

Dam age

-

-

Nutrients (phosphorus) decline, thereby decreasing tailwater productivity

 

Altitude

+

-

Colder water temperatures and ice decrease fall-spawning BT egg and fry survival; Spring-spawning RBT may benefit from slightly cooler temperatures and decreased BT recruitment at high elevations

 

Latitude

+

+

Northerly dams closer to headwater streams may have cooler, more stable water temperatures; decreases exposure to drought conditions and water withdrawals in southern latitudes of intermountain West

 

Reservoir storage capacity

+

+

Stratification from large, hypolimnetic-releasing dams provides stable water temperatures

Mean adult length

Hydropeaking (variable subdaily flow, based on the coefficient of variation)

+

+

Food base enhanced through pulses of invertebrate drift

 

Relative annual flow

+

+

High invertebrate production, high dissolved oxygen, cooler water temperatures

 

Specific discharge

-

-

High velocity water is energetically costly; decreases condition and growth

 

1st axis, Principal Component Analysis (PC1; ↑ summer flow)

+

+

Channel expands into low-velocity shelf habitats; energetic savings; better prey availability

 

2nd axis, Principal Component Analysis (PC2; ↑ winter, ↓ spring flow)

+

-

Metabolic cost savings during spawning; provision of thermal habitat refugia and better post-spawning habitat

 

Rainbow and brown trout catch (any size)

-

-

Inter and intraspecific competition for prey; density-dependent effects (both species included in models)

 

New adult cohort strength

-

-

Large cohort swamps adult cohort with fish exhibiting shorter lengths; potential density effects on growth

 

Fish stocking

+

+

Stocked fish are typically larger, increasing the mean length of the population

 

Whirling disease

+

+

Decreased recruitment shifts age structure towards larger surviving individuals

 

Dam age

-

-

Nutrients (phosphorus) decline, thereby decreasing tailwater productivity

 

Altitude

-

-

Metabolic costs associated with cold water temperatures may decrease size

 

Latitude

+

+

Northerly dams closer to headwater streams may have cooler, more stable water temperatures; decreases exposure to drought conditions and water withdrawals in southern latitudes of intermountain West

 

Reservoir storage capacity

+

+

Stratification from large, hypolimnetic-releasing dams provides stable water temperatures


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