The Population Ecology and Nutrient Transport of Gulf Menhaden in Fourleague Bay, Louisiana (Mortality, Growth, Feeding, Production, Migration).

An ecological study of the young-of-the-year of three year-classes of gulf menhaden (Brevoortia patronus) was conducted from July 1981 to December 1983 in Fourleague Bay, Louisiana. This study documented gulf menhaden population ecology and the importance of gulf menhaden in the nutrient and energy balance of estuaries. Young-of-the-year gulf menhaden immigrated in winter and moved to tidal creeks and ponds, where they remained until midsummer. They then moved into open bays, where they remained until the fall. This migration pattern coincides with sequentially available, but spatially separate, productivity peaks in marsh and open bays. In the fall, they emigrated to offshore coastal areas. Emigration is size-related, with larger individuals moving out first. The instantaneous growth coefficient (G), determined from otolith and length-frequency studies, ranged from 0.00454 to 0.00517 % day(\u27-1). Mortality rate was between 0.008 and 0.018 % day(\u27-1). In 1983, when river discharge was high and winter temperatures and salinities were low, fish grew more slowly and the mortality rate was higher. Major body composition changes from larvae to subadult included an increase in lipid content and energy content, and a decrease in nitrogen content. Young-of-the-year gulf menhaden did not exhibit the condition factor pattern typical of adult clupeids. Lipid condition (KF) peaked in midsummer, then declined, and increased again in the fall. The decline of KF in the fall may be because gulf menhaden with higher lipid contents migrated out of the estuary first. Gulf menhaden may export significant quantities of energy and nutrients from estuaries to the offshore ecosystem. The amount varies with growth and mortality rates and the abundance of fish. Typical values are 9.9 g biomass, 261.5 kJ, 5.6 g C, 1.0 g N, and 0.3 g P, m(\u27-2) marsh yr(\u27-1). These exports indicate that fish transport may be an important component of the nutrient budget of estuaries