Impacts of population-level reproductive success on recruitment dynamics in Largemouth Bass (Micropterus salmoides)

摘要

Understanding the mechanisms that govern recruitment in fish populations is fundamental to informing management decisions that are designed to provide sustainable recreational fisheries. The Largemouth Bass (Micropterus salmoides) is a popular and widely exploited sport fish that provides exclusively paternal care to its offspring during the reproductive season each spring. While recreational anglers can negatively impact reproductive success of individuals by capturing nesting males, interrupting parental care, and thus facilitating higher embryonic mortality rates through brood predation, it is unclear whether or not variation in reproductive success across a population is an important driver of recruitment. Density-dependent survival of age-0 Largemouth Bass after parental care ceases may compensate for variation in reproductive success earlier in the first year of life. The chapters of this dissertation present the findings of one study that investigates mechanisms determining brood loss and the concomitant reduction in individual reproductive success during a recreational angling event, and two other studies that examine how reproductive success across a population determines recruit abundance. In Chapter 2, I found that 65% of bass nests in natural lakes experienced brood predation, and that higher brood predator density in the vicinity of the nest was associated with increased probability of brood predation, leading to higher rates of abandonment. Angled male Largemouth Bass were held in a live well for 15 minutes and returned to defend their broods after being released in 30 minutes on average. In addition, the consumption rate of brood predators was higher in nests with higher mating success (i.e., number of embryos), but the number of fry consumed was positively correlated with brood predator densities near the nest prior to angling. The size of the remaining brood determined whether or not the male abandoned its nest, while predator density, parental male quality, and initial brood size had little influence on abandonment decisions, indicating that even catch-and-release angling of nesting bass can have a negative effect on reproductive success. In Chapter 3, I experimentally induced episodic mortality of 50% of embryos across populations of Largemouth Bass in a series of research ponds, which resulted in a 39% reduction in recruit abundance and a 37% reduction in recruit biomass compared to control ponds. Although higher survival rates in the treatment ponds did appear to partially mitigate recruit losses due to that episodic mortality of embryos, compensatory survival was not great enough to overcome the overall reduction in recruit abundance caused by the treatment. In Chapter 4, I utilized long term fish community assessment data in an information theoretic modeling approach to define which combinations of predictor variables from several stages within the first year of life had the strongest relative influence on fall age-0 Largemouth Bass abundances. It was determined that 1) the presence of Gizzard Shad (Dorosoma cepedianum) had a strong negative effect on age-0 Largemouth Bass abundance in the fall; 2) regression models that included juvenile Bluegill (Lepomis macrochirus) abundance and turbidity best explained variation in age-0 Largemouth Bass abundance when compared to other models and that both variables were positively correlated with recruit abundance; and 3) density of nesting Largemouth Bass was positively correlated with recruit abundance but was less effective at explaining variation in age-0 Largemouth Bass abundance. While predator-prey interactions during the first summer had clear implications for determining year class strength in Largemouth Bass, reproductive success also played a role in recruitment dynamics of the species.;Overall, these findings demonstrate the importance of reproductive success in recruitment dynamics of Largemouth Bass and that especially in systems with intense angling pressure and high brood predator densities, density dependent growth and survival may not ameliorate early mortality due to brood predation. Furthermore, these findings show that the relative importance of sources of mortality occurring at various stages of the first year of life have variable impacts on determining recruit abundance, likely due to differences at large spatial and ecological scales.