ASSESSMENT OF EUROPEAN LOBSTER (HOMARUS GAMMARUS) RESTOCKING EFFORTS USING PARENTAGE ANALYSIS AND GENETIC DIVERSITY IN SOTENÄS, WEST COAST OF SWEDEN

Sammanfattning

The European lobster is a highly valuable resource along the west coast of Sweden, with a fishery dating back to the 17th century. However, natural stocks have undergone a longterm decline, leading to increasingly strict management regulations over time. In this context, restocking has emerged as a conservation strategy aimed at supporting and rebuilding natural populations. Although such efforts have been implemented for many years, their effectiveness has remained controversial largely due to methodological limitations in evaluating long-term outcomes. Recent advances in population genetics now enable long-term, non-invasive monitoring of both wild populations and enhancement programmes. In 2018, a European lobster restocking project was initiated on the west coast of Sweden, during which thousands of hatchery-reared juveniles were released over a three-year period. This study aimed to evaluate the success of this programme by detecting released individuals in the sampled population using parentage analysis. A total of 146 lobster tissue samples were collected from the coastal area around Smögen during 2025. Genetic analyses were conducted using a panel of 96 SNP loci previously tested for assessing parentage relationships between sampled individuals and the broodstock females used during the restocking programme. Genotype assessment based on multiple COLONY runs, using a likelihood-based approach for parentage inference, identified 10 offspring assigned to two broodstock females (M-S22 and MS27) used during the final year of the project (2020). In addition, full-sibling and halfsibling relationships were detected among individuals associated with females not included in the programme. A total of 123 potential sires were also identified, suggesting that a large number of males contributed to the studied population. Overall, this study suggests that genetic tools can provide a valuable and potentially cost-effective approach for evaluating restocking programmes. In the long term, these tools may also help assess the contribution of hatchery-reared individuals to the gene pool of wild populations and their potential impact on genetic diversity.