We hypothesized that most recruitment of striped bass Morone saxatilis in the Santee-Cooper system. South Carolina, comes from river-spawn egg cohorts transported at the right time to high-quality nursery habitat, generally located in or near Lake Marion, a large reservoir within the system. Because striped bass produce a superabundance of eggs, only a small portion of the total egg production must develop in favorable nursery habitat to produce good recruitment in any year. In a 3-year study, we assessed temporal variability in egg mortality, compared the survival of progeny cohorts, and monitored abundance of juveniles and zooplankton in nursery areas. Growth rates and hatch dates of juveniles were estimated from otoiiths. Mortality rates and hatching locations varied among egg cohorts. In the best recruitment years, 1988 and 1990, highest survival was associated with eggs hatched during the early half of the spawning season in Lake Marion. Zooplankton densities were higher in Lake Marion than in the spawning tributaries, suggesting that the lake was a superior nursery habitat. Growth rate of juveniles was highest in 1990. Water management at upstream dams in the Santee-Cooper system might increase recruitment by optimizing temperature and flow so that the maximum possible number of eggs hatch in upper Lake Marion.

1. Biological resilience is of heightened concern in increasingly anthropogenic landscapes. Quantification of faunal resilience across a wide range of spatial scales and geographical areas is necessary to understand factors influencing the rate and degree of recovery, especially in fragmented ecosystems. 2. We evaluated the recovery of a riverine fish assemblage from a major diesel oil pipeline spill and associated fish kill in 37 km of the Reedy River, South Carolina, U.S.A. The fish assemblage was monitored at four disturbed sites within the fish kill zone and one upstream, undisturbed reference site over a 112-month (9.3-year) period following the disturbance. We used non-metric multidimensional scaling (NMS) ordination to evaluate change in fish assemblage structure among sites and to determine the degree of recovery in assemblage structure. 3. NMS ordination of species relative abundance in two dimensions represented 93% of the total variation in fish assemblage structure among samples and illustrated recovery of the fish assemblage. Initial dissimilarity in assemblage structure was evident between the disturbed sites and the reference site, reflecting high mortality from the oil spill. The disturbed sites as a group increased in similarity to the reference assemblage with time, while the reference assemblage remained relatively stable. Strongest similarity in assemblage structure between the disturbed group and the reference group was achieved by October 2000 (52 months post-disturbance), indicating recovery from the oil spill. Remaining variation in assemblage structure was consistent with longitudinal site position and comparable to that of an undisturbed reference river, attributable to inherent longitudinal variation along the 37-kilometre river section. 4. Recovery rate among sites varied in relation to proximity and connectivity to recolonisation sources on a landscape scale. Recovery of the uppermost disturbed site was faster than the other disturbed sites because of its proximity to the undisturbed main stem fish assemblage, whereas the three most downstream sites were slower to recover largely because of isolation by anthropogenic barriers. These observations illustrate the influence of fragmentation on fish assemblage resilience at large spatial scales.

Life history and harvest characteristics of a reproducing population of striped bass Morone samailis in the Santee–Cooper system, South Carolina, were assessed to determine the relative merits of selected management strategies. Equilibrium yield and Leslie matrix analysis were the primary analytical tools. The analyses indicated that. without stocking, recruitment overfishing would occur al the current harvest rate, causing population decline. Restricting harvest until age 4 or greater produced population growth under a wide range of mortality rates. Current stocking levels stabilized or stimulated population growth. The magnitude of the effect of stocking was dependent on the level of' harvest restriction. A combination of a 2‐year stocking pulse and increased harvest restriction provided short‐term numerical benefits and reduced the long‐term risks of genetic swamping.

The Santee–Cooper system in South Carolina, USA, is a complex of reservoirs, rivers, and canals. The endangered shortnose sturgeon Acipenser brevirostrum inhabits the rivers below the reservoirs and has also occasionally been reported anecdotally in the reservoirs themselves. During 1998–1999, we conducted a study to determine whether shortnose sturgeon were reproducing in the reservoirs, and if so, to evaluate habitat use and degree of separation from the riverine groups. Fourteen shortnose sturgeon were captured from the reservoirs, and all (even gravid females) appeared qualitatively less robust than riverine fish previously captured below one of the dams. Ten of the fish were implanted with transmitters and tracked at least once per week. Fish tracked in the upper reservoir, Lake Marion, stayed in the upper portion of that lake or in tributary streams flowing into it. We documented seasonal movements among four primary areas of upper Lake Marion and its tributaries. A spawning site on one of the tributaries, the Congaree River, was verified by collection of viable eggs. Genetic analysis demonstrated significant differences between samples from the Santee–Cooper reservoirs and three nearby coastal rivers. Cooper River samples, however, were not significantly different from reservoir samples, although appreciable differences in haplotype frequencies were observed. The need for a larger sample size was apparent. Although telemetry, spawning, genetic, and observational evidence suggests that the shortnose sturgeon in the reservoirs form a separate population segment, the results are not conclusive because possible downstream movement, especially of juveniles, through the dams has not been investigated.

A major factor that contributes to loss of genetic variation in natural populations is a small effective population size. In species with a complex life history that involves overlapping generations and delayed maturity, the impact of infrequent annual reproductive bottlenecks is likely to be small because effective population size is defined by the number of individuals contributing to a generation and not to a single year‐class. The striped bass Morone saxatilis is a long‐lived species with overlapping generations and age structure, whose recreational and commercial importance has made it a target of intense harvest. We analyzed allele frequency fluctuation among juvenile year‐classes of the Santee–Cooper, South Carolina, population from 1990 through 1994 with three independently segregating polymorphic nuclear DNA loci to examine genetic drift and estimate the number of breeders each year. Significant fluctuations in allele frequencies among juvenile year‐classes were observed, and most of the variation was attributed to a small number of parents in 1992. The potential impact of this year‐class is likely to be low because 1992 was a poor recruitment year, and striped bass have multiple opportunities to breed. However, high adult mortality due to fishing may increase the impact of the 1992 year‐class by decreasing the number of adult age‐classes in this population. Thus, high exploitation in species with overlapping generations can reduce the long‐term effective population size by abrogating the possibility of multiple breeding opportunities.