Defining a spawning population (spotted seatrout Cynoscion nebulosus) over temporal, spatial, and demographic scales

Fish spawning populations are complex and affected by many factors acting over temporal, spatial, and demographic scales. To better understand these factors, we chose to study spotted seatrout Cynoscion nebulosus, which has closed populations over small spatial scales and a periodic life-history pattern. We used experimental gill nets and hook and line, within a spatially and temporally explicit sampling design, to collect 2034 spotted seatrout in lower Tampa Bay, Florida, USA, in 2001 and 2002. Ovarian development was evaluated histologically. Mature females did not all spawn throughout the spawning season, and first-time spawners (Age 1) had the lowest probability of doing so. Two reproductive behaviors were observed: fish moving in the late afternoon or evening to a high-intensity spawning site in an inlet and low-intensity spawning within the estuary. Larger, older female and male spawners were more abundant at the inlet site than at nearby estuarine sites. Both batch fecundity and the percentage of females spawning increased with age and size. Spatial-temporal interactions made it difficult to assess certain aspects of reproduction, such as spawning frequency.