Incorporating Early Life History and Recruitment in Analysis of Population Dynamics of Wetland Fishes

Hydrological variation is believed to be the major abiotic factor influencing fish recruitment in floodplain ecosystems. However, past studies fail to address the impact of hydrology on the three major drivers of recruitment: age-specific growth and mortality, and dispersal. I examined long-term recruitment dynamics for six fish species inhabiting the Everglades by addressing the impact of hydrology on these important characteristics. I then linked these changes to annual fluctuations in population size. Before interpreting time-series data on recruitment, I evaluated the impact of size-selective bias from sampling gear on our interpretation of hydrological drivers of recruitment. Analyses revealed that individuals under the size of maturation were under represented, but these individuals could be estimated using a stage-based model. Analyses of the corrected data revealed that recruitment primarily occurred in October for most species, driven by changes in water depth and the number of days post-drying. Recruitment variability in fish stocks is commonly assumed to be controlled by density-dependent processes. I examined density-dependent feedback on recruitment by evaluating stock-recruitment models. I found strong evidence for density-dependence along a wide hydrological gradient. This feedback was driven by recruitment from the previous season and was strongest at short and long hydroperiods. Immigration/emigration also explained residual variance in these models. To quantify dispersal, I evaluated the recolonization patterns following disturbance. The sequence of species arrival was highly repeatable. Interspecific differences in both speed and directedness estimated by swimming tests and field data best described arrival order of these species. Directedness was more strongly correlated with faster recolonization than speed. The transitional age when mortality equals weight-specific growth (M’/G’=1) is an important indicator of recruitment success. Analyses revealed that the transitional age was correlated with annual changes in species abundance. The timing of the transitional age occurred later in life as disturbance frequency increased, with highly dispersing species unaffected. My research has detailed how hydrology influences the three indicators of recruitment success. Interpretation of these results can only be accomplished after accounting for bias in sampling gear, identifying the source of density-dependent mortality, and accounting for movement from long-distance dispersal