Limited genetic structure of Gulf Menhaden (Brevoortia patronus), as revealed by microsatellite markers developed for the genus Brevoortia (Clupeidae)

The views and opinions expressed or implied in this article are those of the author (or authors) and do not necesarily refl ect the position of the National Marine Fisheries Service, NOAA. Abstract—Long-term sustainable management of wild populations should be based on management actions that account for the genetic structure among populations. Knowledge of genetic structure and of the degree of demographic exchange between discreet populations allows managers to better define management units. However, adequate gene loci for population assessments are not always available. In this study, variable co-dominant DNA loci in the heavily exploited marine genus Brevoortia were developed with a microsatellite-enriched DNA library for the Gulf Menhaden (Brevoortia patronus). Microsatellite marker discovery was followed by genetic characterization of 4 endemic North American Brevoortia species, by using 14 novel loci as well as 5 previously described loci. Power analysis of these loci for use in species identification and genetic stock structure was used to assess their potential to improve the stock definition in the menhaden fishery of the Gulf of Mexico. These loci could be used to reliably identify menhaden species in the Gulf of Mexico with an estimated error rate of α=0.0001. Similarly, a power analysis completed on the basis of observed allele frequencies in Gulf Menhaden indicated that these markers can be used to detect very small levels of genetic divergence (Fst≈0.004) among simulated populations, with sample sizes as small as n=50 individuals. A cursory analysis of genetic structure among Gulf Menhaden sampled throughout the Gulf of Mexico indicated limited genetic structure among sampling locations, although the available sampling did not reach the target number (n=50) necessary to detect minimal values of significant structure. Management of wild populations is improved when management actions take into account genetic structure. Stock assessments of marine species are improved when genetic data are used in the development of a fi shery stock defi nition (Begg and Waldman, 1999; Waples et al., 2008). Different outcomes in stock assessments are expected between a scenario with a single exploited population and a scenario in which 2 or more demographically independent populations are exploited simultaneously by a fi shery. In the latter case, treating 2 or more independent fi shery stocks as a single unit could potentially lead to underestimates of the effects of exploitation on local stocks and an overall diminished yield (Carvalho and Hauser, 1994). Therefore, genetic analyses of population structure can improve stock assessments by increasing accuracy in identifi cation of the number of populations exploited and the extent and direction of demographic exchange (migration) among exploited populations (Begg and Waldman, 1999; Waples et al., 2008). A recent Southeast Data, Assessment, and Review (SEDAR) stock assessment indicated that more genetic data are needed to appropriately defi ne the stock harvested by the menhaden fi shery (Brevoortia spp.) in the Gulf of Mexico (Vaughn et al.1). Two