Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
A conceptual life history of the Atlantic croaker (Micropogonias undulatus) identifies the effects of the environment on juvenile recruitment. In a multi-disciplinary approach to modelling, the major effects are investigated, quantified and presented in a flow chart. The model is divided into three sub models, each representing a major component which affects juvenile recruitment. North/south spawning location in the Mid-Atlantic Bight is affected by the bottom water temperature as influenced by the cessation of the summer winds in relation to timing of croaker migration. The pelagic phase is the most critical time in the life history of a larval croaker as they are subjected to wind-induced transport which may cause direct loss off the shelf and entrainment in the Gulf Stream, or indirect loss by prolonging time in transit to the nursery area. The magnitude of this wind-included effect is a function of the direction, strength, duration and time relative to spawning and is incorporated in an equation to predict year-class strength of croaker. The juvenile croaker overwinter in the Chesapeake Bay system. Winter temperature is shown to be the predominant variable affecting year-class survival to the following summer in very cold years. However, in very warm years, the predictive capabilities of the model are improved when a measure of fall recruitment, i.e. wind-induced transport, is incorporated. Croaker is basically a density-independent stock as, juvenile recruitment is erratic and dependent upon these environmental parameters. The effect of spawning stock size is only apparent after accounting for density-independent effects, and slightly improves the explained variance of the statistical relationship. Year-class strength and fishing pressure cause interannual variability in commercial catch. Overfishing a weak year class reduce spawning potential, and several poor year classes in a row magnify this. The moel, tested for the 1982-83 data, predicts a strong year class.
© The Author
Norcross, Brenda L., "Climate scale environmental factors affecting year-class fluctuations of Atlantic croaker (micropogonias undulatus) in the Chesapeake Bay (Maryland, Virginia)" (1983). Dissertations, Theses, and Masters Projects. Paper 1539616796.