The Relative Influence of Thermal Experience and Forage Availability on Growth of Age 1–5 Striped Bass in Two Southeastern Reservoirs
Jessica S. Thompson and James A. Rice
Abstract.—Warm epilimnetic temperatures and hypolimnetic hypoxia during summer stratification have been linked to poor growth and condition of inland striped bass Morone saxatilis. Contrary to expectations, however, growth occurs in some reservoirs with intense temperature–oxygen stratification in which hypoxia forces striped bass into temperatures well above their preferred range. One potential explanation for this apparent contradiction is that high forage availability may mediate the energetic costs of exposure to warm summer temperatures in some systems. To test this hypothesis, we assessed the relative influence of thermal experience and food consumption on growth of striped bass in Badin Lake and Lake Norman, North Carolina, using bioenergetics model simulations. Badin Lake is eutrophic with striped bass restricted by hypoxia to warm temperatures in the summer, but striped bass experience modest positive growth over the summer and substantial annual growth. Lake Norman is oligotrophic and striped bass are restricted to warm temperatures by hypoxia for a shorter period, but they experience almost no summer growth and minimal annual growth after age 3. Model simulations showed that Badin Lake striped bass ages 1–4 achieved high food consumption rates during the summer that continued into the fall as temperatures cooled, allowing for rapid fall growth. Lake Norman striped bass ages 1–5 experienced lower consumption rates over the summer and fall. Consumption was not sufficient to allow larger striped bass to allocate energy to growth over the summer, and these fish did not experience any season with a combination of cool temperatures and high food consumption. Habitat exchange simulations modeled how much the growth of a particular size fish in one reservoir might change if it had experienced the temperatures or food consumption of a similar sized fish in the other reservoir. These simulations showed that the relative effect of food consumption on striped bass growth was three times that of exposure temperature in the first year of the study and 37 times that of temperature in the second year. Poor striped bass growth and condition is not, therefore, linked solely to poor physical habitat. Rather, management of reservoir striped bass populations will be improved by balancing demand for and availability of prey resources for striped bass, and this balance will be especially important in reservoirs where summer hypoxia forces fish into warm temperatures that increase metabolic costs.