Population Dynamics of Spot, Leiostomus xanthurus, in Polyhaline Tidal Creeks of the York River Estuary, Virginia

Abstract

Most populations of estuarine-dependent, early life stages of marine fishes are open. As a result, it has been difficult to apply conventional population models to most systems. In this study, a marked population of young-of-year spot (Leiostomus xanthurus) was released into a polyhaline tidal creek within the Guinea Marshes of the York River estuary, Virginia. Over a 90-day study period, 221 marked fishes were recaptured. Plots of the ratio of marked to unmarked individuals (mi/ni) in subsequent samples indicated that the population was resident in the creek for up to 162 days with the average individual present for 81 days. When this population turnover rate was compared to the total population decay rate (marked plus unmarked fish), it was determined that exchange between habitats (immigration/emigration) accounted for about 36.4% of the total decay rate, with the remainder attributed to natural mortality. By correcting the overall disappearance rate for population turnover due to emigration and using this adjusted value as a measure of instantaneous mortality (z), the estimated production (over 90 days) in this population was 23,630 cal (98,870 J) per m2. This figure agrees with a previously derived estimate for spot in the Guinea marshes and is nearly two orders of magnitude higher than other reported values for this species for all size classes over the entire growing season.