Theses and Dissertations

Title: Influences of spatial and temporal heterogeneity on age-0 largemouth bass growth and recruitment in a tidal-freshwater to low-salinity estuary

Name: Peer, Adam C.

Degree: MS

Chair: Dennis R. DeVries and Russell Wright


University: Auburn University

Location: Auburn, Alabama

Date: 2004

Pages: 115

Keywords: spatial and temporal heterogeneity, largemouth bass, growth, recruitment, tidal-freshwater, low-salinity estuary


Spatial and temporal heterogeneity in ecological systems can have strong influences on population demographics. For populations distributed across a wide spatial scale, this heterogeneity can lead to differential populations processes, especially if movement between subpopulations is limited. Tidal freshwater and low-salinity brackish water estuaries are complex systems characterized by extreme variation in physicochemical factors (i.e., temperature, salinity, dissolved oxygen, discharge, turbidity, and nutrient concentrations) that can influence organism growth, survival, and abundance, while indirectly affecting them through modifications of predator-prey relationships and competition. Although ecological factors are influenced by spatial heterogeneity of multiple variables, the timing of these factors also plays a role in the growth and recruitment of fishes. For age-0 largemouth bass (Micropterus salmoides) and other piscivores, growth, survival, and ultimately recruitment success often is determined by one or more critical early-life periods. These critical periods include time of hatching, onset of piscivory, fall lipid accumulation, and overwinter survival. In this study, I examined growth and recruitment of a juvenile freshwater predator, largemouth bass in a heterogeneous tidal freshwater to low-salinity brackish water estuary in the Mobile-Tensaw Delta, Alabama. In addition, I explored the significance of historically referenced critical periods (i.e., hatch date, onset of piscivory, and overwinter survival) and examined alternative critical periods or events influencing growth and recruitment. To examine whether physical, chemical, or biological heterogeneity in the delta led to spatial and temporal variation in growth and recruitment of age-0 largemouth bass, I established six sampling sites along an upstream-downstream gradient that encompassed ~ 13 river km. From May 2002 through April 2004 I collected young-of-year largemouth bass monthly. I quantified summer growth using otoliths collected in June and July of each year, whereas length-frequency distributions were used to evaluate growth and size during the remainder of the year. I collected and quantified all other fish species to determine the potential effects of interspecific interactions. In addition, I quantified temperature, salinity, dissolved oxygen, turbidity, water level and zooplankton biomass to examine the variability of important physicochemical and biological variables. During both years of this study, mean daily growth rates of summer age-0 largemouth bass was faster at sites either in, or adjacent to brackish water habitats. Fast spring and summer growth, particularly at the site furthest downstream, was strongly related to high fish prey availability, greater piscivory, and consequently greater energetic content of food consumed (diet calories ? g-1 bass). These growth patterns carried through fall and into spring, producing larger, but nearly equal abundances of age-1 largemouth bass at sites in, or adjacent to brackish water habitats during summer. Unlike most other southern latitude systems, growth continued through winter, and size-selective mortality appeared to be negligible. In addition, hatch date and transition to piscivory had no influence on growth differences among sites, nor overwinter survival, or age-1 recruitment. Spatial heterogeneity in physical, chemical, and biological variables, however, appeared to have a strong influence on summer prey availability, the degree of piscivory, and consequently growth variability in the delta. Temporal growth trends showed that, with the exception of the site furthest downstream, the 2003 year-class grew slower and exhibited smaller sizes throughout the year in comparison to the 2002 year-class. Slower growth and smaller sizes appeared to be due to hydrologic conditions during spring and early summer. High water and low water temperatures during this period appeared to lead to more protract

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