Effects of low flow on Fountain Darter fecundity

1
Effects of low flow on Fountain Darter
fecundity

2
Background

• Fountain Darters (Schenck and Whiteside 1977)
• Spawn year round based on presence of ova
• Two peaks Aug and Jan Apr
• Warmer water temperatures (gt23)?
• Decreases in flow (lt200 cfs)?

3
(No Transcript)
4
Background

5
Background

6
Spring-associated fishes spawning

• Photoperiod initiates
• Temperature stops
• Plenty of unexplained variation

7
Questions?

• Effects of low flow on Fountain Darter
  reproduction?
• Flow is likely not a proximate cue for spawning
• However, flow is a master variable
• Physical, chemical, and biological environments
• Difficult to test in laboratory setting

8
(No Transcript)
9

• Reproduction
• Related to flow?
• Related to vegetative structure?

10
Methodology

• Fish will be collected
• monthly from Jan Aug (Dec)
• from 4 locations (5 to 120 cfs)
• from three vegetation types (tall, short, no)

11
Methodology

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

D. C. Heins, Tulane U.
12
Analyses and Outcomes

• ANOVA (cfs, vegetation type)
• Covariates time and potentially other factors
• Refinement of year-round spawning
• Effects along a flow gradient
• Effects of vegetation

13
(No Transcript)
14
Effects of predation on fountain darter
population size at various flow rates

15
Piscivorous fishes

• Predation varies (Schlosser and Ebel 1989)
• Temporally, dependent of flow regime
• Spatially, dependent on habitat
• Average flows predation on Fountain Darters is
  low (BIO-WEST 2002)
• 3 darters out of 437 potential predators
• 3 darters out of 126 confirmed predators

16

• San Marcos River (BIO-West 2006) lt100 cfs
• consumption not detected
• ltlt100 cfs
• Increase predation likely, decimation of
  potential and confirmed fish predators?

17

• Trophic cascade

Rahel and Stein 1988, Taylor and Soucek 2010,
Thomas 2011
18
Questions?

• Numbers of darters consumed by?
• Crayfish only
• Largemouth Bass only
• Crayfish bass
• Does vegetation mediate the response?

19
Methods

• Laboratory setting (FAB)
• Phase 1 Observational studies
• Numbers of prey and predators, amount of
  vegetation, exposure time

20
Methods

• Phase 2
• Predictions
• Consumption (crayfish) gt Consumption (bass) gt
  Consumption (bass x crayfish)
• Consumption (bare) gt Consumption (vegetation)

21
Experimental design

• Completely randomized design
• Experimental unit aquarium with darters
• TRT
• 1 no pred, cray, bass, cray bass
• 2 veg/bare

22
Experimental design

• Replication 3
• 2-factor ANOVA (a 0.05) with Fishers LSD