Genetic population structure of anadromous striped bass along the US Atlantic coast was analyzed using 14 neutral nuclear DNA microsatellites. Young-of-the-year and adult striped bass (n = 1114) were sampled from Hudson River, Delaware River, Chesapeake Bay, North Carolina, and South Carolina. Analyses indicated clear population structure with significant genetic differentiation between all regions. Global multilocus F ST was estimated at 0.028 (P < 0.001). Population structure followed an isolation-by-distance model and temporal sampling indicated a stable population structure more than 2 years at all locations. Significant structure was absent within Hudson River, whereas weak but significant genetic differences were observed between northern and southern samples in Chesapeake Bay. The largest and smallest effective striped bass population sizes were found in Chesapeake Bay and South Carolina, respectively. Coalescence analysis indicated that the highest historical gene flow has been between Chesapeake Bay and Hudson River populations, and that exchange has not been unidirectional. Bayesian analysis of contemporary migration indicated that Chesapeake Bay serves as a major source of migrants for Atlantic coastal regions from Albemarle Sound northward. In addition to examining population genetic structure, the data acquired during this project were capable of serving as a baseline for assigning fish with unknown origin to source region.

The South Carolina Department of Natural Resources has been stocking red drum Sciaenops ocellatus since 1988 to evaluate parameters critical to their successful survival and recruitment in South Carolina estuaries. From 1999 to 2002, between 600,000 and 1,000,000 juvenile red drum were stocked each year in two tributaries of Charleston Harbor. The harbor and each tributary were partitioned into three independent strata and randomly sampled monthly for two decades, allowing population trends before, during, and after stocking to be evaluated. Using microsatellitebased parentage analysis, we examined the contribution of stocked age-0 juvenile red drum (15-60 mm total length) to the local population 1 year after release by using fishery-independent sampling. Analysis of these data showed that the highest contributions (88.9%) were close to the stocking site in years with low natural recruitment, whereas in years with high natural recruitment, contributions were lower and stocking was less effective in increasing catch per unit effort. The results of stocking 600,000 small juveniles/year from 1999 to 2001 in one of the study tributaries (Ashley River) indicated that stocked fish did not displace wild fish but had an additive effect on their abundance, supporting the hypothesis that trophic resources are not limiting for postlarval age-0 red drum within Charleston Harbor. The high observed variability in contribution among years of stocking similar-sized red drum suggests that (1) interpretation on a year-class-specific basis is necessary to fully understand the effects of stocking and (2) marine stock enhancement programs would benefit substantially from evaluation in the context of wild annual recruitment patterns.

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Mutualisms are ubiquitous in nature but are understudied in freshwater ecosystems. Mutualisms can be unstable, shifting to commensal or even negative outcomes with context. Quantifying context dependency in mutualisms is critical for understanding how biotic interactions will shift along disturbance gradients in freshwater systems. A common reproductive interaction among stream fishes, nest association occurs when individuals of one species spawn in nests constructed by a host fish. Hosts benefit from a dilution effect: high proportions of associate eggs decrease the odds of host brood predation. Thus, partner abundance can be an important source of biotic context influencing the outcome of an association. We conducted a large in situ experiment manipulating abundance of partner yellowfin shiner (Leuciscidae: Notropis lutipinnis) (absent, low, high) at constant abundance of host bluehead chub (Leuciscidae: Nocomis leptocephalus), and quantified chub reproductive success using genetic tools. Evidence suggests that the nest association switched from mutualistic to parasitic outcomes as shiner abundance decreased. Chub reproductive success was highest at high shiner abundances. However, chub reproductive success was actually higher in the complete absence of shiners than at low shiner densities. This study shows that outcomes of biotic interactions in freshwater systems are context‐dependent, and that partner abundance can be a key source of context‐dependency in nest associations. We encourage future studies on freshwater mutualisms, which are thus far largely overlooked, relative to competition and predation.

Across a species' range, the population dynamics of some areas may express spatial synchrony (i.e. they fluctuate with one another), whereas other areas may express no synchrony (they fluctuate independently). The degree of synchrony and spatial extent of synchrony are important considerations when assessing the population as a whole. We examined these aspects in red drum Sciaenops ocellatus along the coast of South Carolina using long-term survey data of juvenile abundance in estuarine areas separated by up to ~200 km. Synchrony of year class strength was detected among areas, but the degree of synchrony declined significantly with distance. By comparison, genetic segregation along the coast was either weak or undetectable (based on allele frequencies at 8 microsatellite loci), although it depended on the year class (2004, 2005 or 2007) of fish that was tested. By standardizing juvenile abundance data across estuaries and survey types, a single, regionwide juvenile time series was generated that covered the 1985-2007 year classes. The juvenile time series correlated significantly with the year class composition of the present-day adult population, which was determined using otoliths collected by a separate survey operating in deeper adult habitats. Future work integrating data across even broader spatial scales would assist in the understanding of large-scale ecological processes that control fluctuations in red drum populations, and would provide useful information for fishery managers.KEY WORDS: Sciaenops ocellatus · Red drum · Synchrony · Population dynamics · Recruitment · Genetics · Microsatellites · South Carolina Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 415: [221][222][223][224][225][226][227][228][229][230][231][232][233][234][235][236] 2010 spatial synchrony or are mobile (e.g. competition or predation) (Ranta et al. 1995, 1997, Hudson & Cattadori 1999, Liebhold et al. 2004. Distinguishing between these factors is difficult and their combined effects may lead to non-intuitive responses (Ranta et al. 1995, Hudson & Cattadori 1999.Large-scale spatial autocorrelations of density-independent environmental conditions have been widely studied as a mechanism that can lead to spatial synchrony. The underlying theory, which was first formulated by Moran in his study of Canadian lynx and hare population cycles (Moran 1953a,b), predicts that local populations with similar density-dependent structures should become synchronized under the influence of a spatially autocorrelated, density-independent factor (Royama 1992, Hudson & Cattadori 1999. This theory is relevant to fisheries because environmental conditions are well known to have major effects on fish population dynamics. In particular, the conditions experienced by the early life stages are critical in determining recruitment success because mortality rates are extremely high. Consequently, any environmental factor that modifies early mortality can have a disproportionate effect on the number...

The Black Drum Pogonias cromis is an estuarine-dependent fish that supports recreational and commercial fisheries throughout its range along the U.S. Atlantic coast and Gulf of Mexico (GOM) coast. We used nuclear microsatellite markers and samples collected from multiple locations along both the U.S. Atlantic and GOM coasts to evaluate the stock structure of Black Drum and to examine small-scale spatial genetic population structure along the U.S. Atlantic coast. As no microsatellite primers had been developed for Black Drum, primers for Spotted Seatrout Cynoscion nebulosus and Red Drum Sciaenops ocellatus were screened, selected, and optimized for use with Black Drum DNA. Six polymorphic loci were identified and used to genotype samples. Results suggested (1) significant genetic divergence between Black Drum populations from the U.S. Atlantic coast and the GOM coast; and (2) either recent or current gene flow between the two regions. Along the U.S. Atlantic coast, there appeared to be weak but significant genetic divergence among Black Drum from southern states, specifically between individuals from the Carolinas and Florida. An isolation-by-distance pattern was also observed for Black Drum from North Carolina to Florida. On a larger scale, results suggested a lack of genetic divergence between individuals from Delaware and Virginia and those from the southern Atlantic states, which may be attributable to the life history patterns of Black Drum. Our results support the management of Black Drum in U.S. waters as two separate stocks: Atlantic and GOM. The results also support the management of Black Drum along the U.S. Atlantic coast as a single unified stock and indicate the need for common management regulations among the Atlantic states.

The American shad Alosa sapidissima is an anadromous clupeid with once‐prolific stocks that have experienced major coastwide declines in abundance over the past century. The American shad spawning run in the Edisto River (South Carolina) has been exhibiting the same decreases as spawning runs in other coastal rivers, and stocking is now being considered as a restoration option for this river system. We utilized a suite of 13 microsatellite loci to provide a baseline genetic characterization of the Edisto River spawning run prior to supplementation and to evaluate the initial success of an experimental stocking program enacted from 2008 to 2010. No significant temporal genetic differentiation was found between sampling years, indicating that the genetic composition of the Edisto River spawning run is temporally stable over short time frames. Estimates of genetic diversity for Edisto River American shad were high (observed heterozygosity = 0.82–0.85) and similar to those observed in other river systems. Estimates of effective population size (3,505–8,379) resembled those reported for other diadromous species and were within the levels recommended for maintaining evolutionary potential. Hatchery‐produced individuals were detected within the 2010 year‐class of juvenile American shad prior to out‐migration (11/314 fish, or 3.5%), demonstrating initial success of the stocking effort (i.e., contribution of hatchery fish to the wild stock). Our results provide valuable information that can be incorporated into management plans for aiding the recovery of American shad in the Edisto River.

The South Carolina Department of Natural Resources began a stock enhancement research program for red drum, Sciaenops ocellatus, as a possible management strategy for augmenting the availability of juveniles for recreational harvest in South Carolina estuaries. Between 1999 and 2011, approximately 6 million juveniles and 260 million larvae were stocked into the Charleston Harbor (CH) estuary, and proportions of stocked fish were found through standardized sampling as high as 49.6% within a subadult year‐class and up to 12% within the spatially separate spawning population. This study evaluated the genetic influences of stocking on the spawning population, using microsatellite loci, and examined any changes in genetic diversity metrics over the course of the stock enhancement program. Percent contribution of stocked fish among subadult and adult collections was compared against measures of genetic diversity. No statistically significant correlations were found among genetic diversity metrics, suggesting that responsible stocking of red drum as small juveniles has not altered the genetic diversity of adults spawning offshore the CH. Life‐history characteristics likely play a large role in mitigating changes in genetic diversity, despite high contributions of stocked fish in some years, because red drum exhibit a long adult life span and benefit from overlapping generations.