Population Genetic Study on the European Flounder (<i>Platichthys flesus</i>) from the Southern Baltic Sea Using SNPs and Microsatellite Markers

The European flounder (Platichthys flesus), which is closely related to the recently discovered Baltic flounder (Platichthys solemdali), is currently the third most commercially fished species in the Baltic Sea. According to the available data from the Polish Fisheries Monitoring Center and fishermen’s observations, the body condition indices of the species in the Baltic Sea have declined in recent years. The aim of the present study was to obtain information on the current patterns of genetic variability and the population structure of the European flounder and to verify whether the Baltic flounder is present in the southern Baltic Sea. Moreover, we aimed to verify whether the observed decline in the body condition indices of the species in the Baltic Sea might be associated with adaptive alterations in its gene pool due to increased fishing pressure. For this purpose, 190 fish were collected from four locations along the central coastline of Poland, i.e., Mechelinki, Władysławowo, the Vistula Lagoon in 2018, and the Słupsk Bank in 2020. The fish were morphologically analyzed and then genetically screened by the application of nineteen microsatellite DNA and two diagnostic SNP markers. The examined European flounder specimens displayed a high level of genetic diversity (PIC = 0.832–0.903, I = 2.579–2.768). A lack of significant genetic differentiation (Fst = 0.004, p > 0.05) was observed in all the examined fish, indicating that the European flounder in the sampled area constitutes a single genetic cluster. A significant deficiency in heterozygotes (Fis = 0.093, p Ne) among the sampled fish groups varied from 712 (Słupsk Bank) to 10,115 (Władysławowo and Mechelinki). However, the recorded values of the Garza–Williamson indicator (M = 0.574–0.600) and the lack of significant (p > 0.05) differences in Heq > He under the SMM model did not support the species’ population size changes in the past. The applied SNP markers did not detect the presence of the Baltic flounder among the fish sampled from the studied area. The analysis of an association between biological traits and patterns of genetic diversity did not detect any signs of directional selection or density-dependent adaptive changes in the gene pool of the examined fish that might be caused by increased fishing pressure

Benchmark Workshop on Atlantic Salmon (Salmo salar) in the North Atlantic (WKBSALMON)

WKBSalmon reviewed the implementation of a Life Cycle Model (LCM) for wild anadromous Atlantic salmon (Salmo salar L.) covering their natal north Atlantic range. The LCM is a time iterative, Bayesian hierarchical model incorporating salmon records of fifteen countries at 25 stock-units. It tracks salmon of two explicit sea-age streams, namely, one-sea-winter (1SW) and multi-sea-winter (MSW), stock unit specific smolt ages, numbers of salmon returning to stock-units, proportions maturing, survival at sea by month and stock unit specific post-smolt survival rates and proportion maturing at 1SW. Mixed-stock catches at West Greenland and Faroes, as well as those in North America, are designated to stock-units based on observed historic tag data, genetic identification and assumed harvest distributions. The LCM will replace three Pre-Fisheries Abundance (PFA) forecast models, aligned to three management units, one eastern North America and two Northeast Atlantic European complex-es of stock-units. The LCM enables a more comprehensive and consistent approach, account-ing for migration and maturation of salmon by stock-unit and a hierarchical (over stock-units) modelling of post-smolt survival and proportion maturing in the first year at sea. The LCM uses outputs from two “Run Reconstruction” models, one for each of eastern North America and Northeast Atlantic origin salmon. These process catch data and exploitation rates and/or returns at stock-unit spatial scales to estimate returning numbers and catches of salm-on by sea-age group. The LCM model uses a similar sea-age group structure for all stock-units resulting in a harmonized life cycle for Atlantic salmon from the North Atlantic. The LCM forecasts estimates of returning salmon by stock-unit based on the post-smolt survival and proportion maturing parameters, forecast forward as a random-walk, from the most recent observations and accounting for “banked” maturing and non-maturing salmon. Forecast returns to stock-units may be compared to Conservation Limit (CL) reference points and “Spawner Escapement Reserves” (SERs – reference points prior to any marine fishing activities) at national and international levels to quantify the risk to the salmon stocks under different mixed-fisheries catch levels. The LCM was found to provide estimates of stock status and forecasts in line with perceptions and previously used modelling frameworks and to be robust to a range of settings and uncertainties.nonPeerReviewe