Effects of low flow on Effects of low flow on Fountain Darter Fountain Darter fecundity fecundity
Dec 27, 2015
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)?
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?
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