Heavy fishing and other anthropogenic influences can have profound impact on a species' resilience to harvesting. Besides the decrease in the census and effective population size, strong declines in mature adults and recruiting individuals may lead to almost irreversible genetic changes in life-history traits. Here, we investigated the evolution of genetic diversity and effective population size in the heavily exploited sole (Solea solea), through the analysis of historical DNA from a collection of 1379 sole otoliths dating back from 1957. Despite documented shifts in life-history traits, neutral genetic diversity inferred from 11 microsatellite markers showed a remarkable stability over a period of 50 years of heavy fishing. Using simulations and corrections for fisheries induced demographic variation, both single-sample estimates and temporal estimates of effective population size (N(e) ) were always higher than 1000, suggesting that despite the severe census size decrease over a 50-year period of harvesting, genetic drift is probably not strong enough to significantly decrease the neutral diversity of this species in the North Sea. However, the inferred ratio of effective population size to the census size (N(e) /N(c) ) appears very small (10(-5) ), suggesting that overall only a low proportion of adults contribute to the next generation. The high N(e) level together with the low N(e) /N(c) ratio is probably caused by a combination of an equalized reproductive output of younger cohorts, a decrease in generation time and a large variance in reproductive success typical for marine species. Because strong evolutionary changes in age and size at first maturation have been observed for sole, changes in adaptive genetic variation should be further monitored to detect the evolutionary consequences of human-induced selection.

Estimating connectivity between juvenile and adult fish habitats can provide an important contribution to effective fisheries management, through a better understanding of population resilience to harvesting pressure. Indirect methods for quantifying connectivity, such as geochemical or genetic techniques, allow us to assign adults from various sampling regions to their natal location, provided that natal origin data can be defined. The elemental composition of otoliths from juvenile sole Solea solea collected at 4 sampling locations in the Southern Bight of the North Sea was measured using laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS), to determine elemental fingerprints indicative of distinct nursery grounds. Significant differences in elemental composition were detected among the 4 locations, with Na, Sr, Ba, Mn and Rb concentrations varying the most between groups. A discriminant model resulted in high assignment proportions of the juvenile fish to their respective nursery grounds with a total jackknife reclassification success of 88%. Even though some interannual variability in otolith chemistry was observed in juveniles from the Scheldt estuary, spatial patterns seemed to dominate. Our results constitute a firm basis for future investigations on nursery area contributions and quality, adult dispersal history and applications of population traceability.KEY WORDS: Connectivity · Juvenile fish · Nursery · Otolith microchemistry · Traceability · Solea solea Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 401: [211][212][213][214][215][216][217][218][219][220] 2010 provide insights into the spatio-temporal connectivity on an evolutionary time scale (in the order of hundreds of generations) (Hedgecock et al. 2007). In marine fish, however, the chances of detecting strong genetic structure, applicable to management decisions, are low because even few migrants suffice to prevent detectable differentiation , Hartl & Clark 2007. Since the 1980s, otolith elemental composition has increasingly been used to describe life histories of fish, study small scale variability in seasonal and within-generation migrations and identify the various environments fish have experienced. The use of trace elements in otoliths is based on the empirical evidence that fish incorporate elements from their environments and that these elements are permanently deposited in their continuously growing otoliths (Campana 1999, Thresher 1999. Consequently, the chemical composition of otoliths differs among fish from different geographical areas and constitutes a powerful multielemental signal reflecting the surrounding physical and chemical environment (Vasconcelos et al. 2007). Juvenile fish that have lived in different coastal environments or estuaries are often characterised by a distinct otolith composition, referred to as the elemental fingerprint. Analysis of otolith composition has been successfully applied in a wide range of flatfish species living in di...

A thorough knowledge on the genetic connectivity of marine populations is important for Wsheries management and conservation. Using a dense population sampling design and two types of neutral molecular markers (10 nuclear microsatellite loci and a mtDNA cytochrome b fragment), we inferred the genetic connectivity among the main known spawning grounds of sole (Solea solea L.) in the North-East Atlantic Ocean. The results revealed a clear genetic structure for sole in the North-East Atlantic Ocean with at least three diVerent populations, namely the Kattegat/Skagerrak region, the North Sea and the Bay of Biscay, and with indications for a fourth population, namely the Irish/Celtic Sea. The lack of genetically meaningful diVerences between biological populations within the southern North Sea is likely due to a large eVective population size and suYcient connection (gene Xow) between populations. Nevertheless, an isolation-by-distance pattern was found based on microsatellite genotyping, while no such pattern was observed with the cytochrome b marker, indicating an historical pattern prevailing in the latter marker. Our results demonstrate the importance of a combined multimarker approach to understand the connectivity among marine populations at region scales.

Historical otolith collections are crucial in assessing the evolutionary consequences of natural and anthropogenic changes on the demography and connectivity of commercially important fish species. Hence, it is important to define optimal protocols for purifying DNA from such valuable information sources while avoiding any damage to the physical structure of the otolith. Before being able to conclude on the harmlessness of a method, it is important to validate protocols on different kinds of otoliths by testing purification methodologies under standardized conditions. Here we compare the effect of two DNA extraction methods on the success in identifying the age in an overexploited marine fish, the common sole (Solea solea L.). To ensure optimal future population genetic and demographic analyses, we assessed DNA quantity and tested the DNA quality by investigating the amplification success of a mitochondrial and nuclear marker. Our results show that the choice of the DNA extraction method had a significant effect on the success of using these otoliths in age and growth analyses. Standard commercial and published protocols resulted in a severe damaging of the otolith structure, hampering accurate preparation and analyses of the morphological structures of the otoliths. Shortening the lysis time and lowering the EDTA (ethylene diamine tetraacetic acid) and SDS (sodium dodecylsulphate) concentration turned out to be beneficial for the stability of otolith structure, while maintaining an overall high DNA quality measured through polymerase chain reaction amplification success. We therefore recommend that care should be taken when choosing the extraction method for a molecular study on archived samples, in order to enable the maximal use of information embedded in historical material.

The movement patterns of released hatchery-reared fish determine the geographical scale at which a population may be enhanced, while the movement patterns of wild fish affect the management strategies of wild populations. This article investigates (1) if movement patterns differ between hatchery reared and wild cod, and (2) if the movement patterns of coastal cod differ between regions. The results from a large mark-recapture experiment in northern Norway showed that displacement distances (DD) for both wild and hatchery-reared fish were highly skewed. The frequency distribution of DD for wild cod was well described by a log-normal distribution. While reared cod that were released at a small size (<27 cm in length) and young age (<1 year of age) had similar movement patterns to wild cod of similar size, reared cod that were larger and older at release dispersed rapidly after release. The frequency of long-distance migrations (DD > 50 km) for larger reared cod was similar, however, to that of wild cod. Fitting log-normal distributions to published mark-recapture data revealed that there was a latitudinal trend, with longer displacement distances in the north than in the south. Cod released in coastal bank areas and offshore island groups also had longer displacement distances than cod released at the Norwegian coast.