Daily ageing to delineate population dynamics of the invasive fish Gambusia holbrooki: implications for management and control.
Despite the high global invasion profile of Gambusia holbrooki, there is limited knowledge of its population dynamics, especially biological parameters for fine-scale delineation of recruitment events that can provide a basis for controlling this short-lived invasive species. Key to this is daily ageing of otoliths, and in this study 193 (~ 50%) of 394 wild fish sampled from an invaded wetland were successfully aged. Increment counts of growth rings in otoliths from aquaria-reared G. holbrooki did not correspond 1:1 to their known ages but were significantly correlated (P < 0.05, R2 = 0.92), suggesting the use of linear relationships could nevertheless be used to estimate the age of wild-caught fish. Mean daily growth rate estimated for spring-summer cohorts (0.28 mm/day) was much greater than that of winter cohorts (0.12 mm/day). A natural mortality rate of 0.01 day- 1 for females was estimated by catch-curve analysis via length to age conversion based on the growth relationship. Birth rate closely correlated with changes in water temperature with a peak reproduction in January (Austral summer) at the study site. This study, for the first time, used daily age estimates of G. holbrooki to quantitatively examine population dynamics, which can be used to investigate invasive dynamics and choice of pest control strategies, including their scheduling and assessment.