Effects of low flow on Effects of low flow on Fountain Darter fecundityFountain Darter fecundity

BackgroundBackground

Fountain Darters Fountain Darters (Schenck and Whiteside 1977)(Schenck and Whiteside 1977)

– Spawn year round based on presence of Spawn year round based on presence of “ova”“ova”

– Two peaks: Aug and Jan – AprTwo peaks: Aug and Jan – Apr Warmer water temperatures (>23)?Warmer water temperatures (>23)? Decreases in flow (<200 cfs)?Decreases in flow (<200 cfs)?

BackgroundBackground

BackgroundBackground

Spring-associated fishes spawningSpring-associated fishes spawning

Photoperiod initiates Photoperiod initiates Temperature stopsTemperature stops Plenty of unexplained variationPlenty of unexplained variation

Questions?Questions?

Effects of low flow on Fountain Darter Effects of low flow on Fountain Darter reproduction?reproduction?– Flow is likely not a proximate cue for Flow is likely not a proximate cue for

spawningspawning– However, flow is a “master variable”However, flow is a “master variable”

Physical, chemical, and biological Physical, chemical, and biological environmentsenvironments

Difficult to test in laboratory settingDifficult to test in laboratory setting

Reproduction:Reproduction:– Related to flow?Related to flow?– Related to vegetative structure? Related to vegetative structure?

MethodologyMethodology

Fish will be collected: Fish will be collected: – monthly from Jan – Aug (Dec)monthly from Jan – Aug (Dec)

– from 4 locations (5 to 120 cfs)from 4 locations (5 to 120 cfs)

– from three vegetation types (tall, short, from three vegetation types (tall, short, no)no)

MethodologyMethodology

Laboratory: Laboratory: – Fish measured (wt, eviscerated wt, TL)Fish measured (wt, eviscerated wt, TL)– Ovary status (I, D, M, S)Ovary status (I, D, M, S)– Oocytes statusOocytes status

D. C. Heins, Tulane U.

Analyses and OutcomesAnalyses and Outcomes

ANOVA (cfs, vegetation type) ANOVA (cfs, vegetation type) – Covariates: time and potentially other Covariates: time and potentially other

factorsfactors

Refinement of year-round spawningRefinement of year-round spawning

Effects along a flow gradientEffects along a flow gradient

Effects of vegetationEffects of vegetation

Effects of predation on Effects of predation on fountain darter population fountain darter population size at various flow ratessize at various flow rates

Piscivorous fishes:Piscivorous fishes:

Predation varies Predation varies (Schlosser and Ebel 1989)(Schlosser and Ebel 1989)::– Temporally, dependent of flow regimeTemporally, dependent of flow regime– Spatially, dependent on habitatSpatially, dependent on habitat

Average flows: predation on Average flows: predation on Fountain Darters is low Fountain Darters is low (BIO-WEST 2002)(BIO-WEST 2002)

– 3 darters out of 437 potential predators3 darters out of 437 potential predators– 3 darters out of 126 confirmed predators 3 darters out of 126 confirmed predators

San Marcos River San Marcos River (BIO-West 2006)(BIO-West 2006) <100 cfs <100 cfs– consumption not detected consumption not detected

<<100 cfs<<100 cfs

Increase predation likely, decimation Increase predation likely, decimation of potential and confirmed fish of potential and confirmed fish predators?predators?

Trophic cascade:Trophic cascade:

Rahel and Stein 1988, Taylor and Soucek 2010, Thomas 2011

Questions?Questions?

Numbers of darters consumed by…?Numbers of darters consumed by…?–Crayfish onlyCrayfish only–Largemouth Bass onlyLargemouth Bass only–Crayfish & bassCrayfish & bass

Does vegetation mediate the response? Does vegetation mediate the response?

MethodsMethods

Laboratory setting (FAB)Laboratory setting (FAB)

Phase 1: Observational studiesPhase 1: Observational studies–Numbers of prey and predators, amount Numbers of prey and predators, amount of vegetation, exposure timeof vegetation, exposure time

MethodsMethods

Phase 2: Phase 2: –Predictions: Predictions:

Consumption Consumption (crayfish) (crayfish) > Consumption > Consumption (bass) (bass) > > Consumption Consumption (bass x crayfish) (bass x crayfish)

Consumption Consumption (bare) (bare) > Consumption > Consumption (vegetation)(vegetation)

Experimental designExperimental design

Completely randomized designCompletely randomized design

Experimental unit = aquarium with Experimental unit = aquarium with dartersdarters

TRT:TRT:

1: no pred, cray, bass, cray & bass1: no pred, cray, bass, cray & bass

2: veg/bare2: veg/bare

Experimental designExperimental design

Replication: 3Replication: 3

2-factor ANOVA (2-factor ANOVA (αα = 0.05) with = 0.05) with Fisher’s LSDFisher’s LSD