This paper provides the results from the first meta-analysis to examine the impact of cormorant (Phalacrocoracidae) predation on fish. It is based on a systematic search of literature, covering studies using significance-based hypotheses tests on the relation between fish parameters and cormorant abundance. The results show that extensive research on cormorant diet exists, but few studies use statistical hypotheses testing to examine the effect on fish populations. In total, 603 publications were identified from titles and abstracts, to include the interaction between cormorants and fish.From these, 27 articles tested fish population parameters against cormorant predation, whereof 22 could be included in analyses. The effect size was defined negative in cases when cormorant numbers or presence reduced fish numbers or biomasses, or when individual fish sizes decreased, and vice versa for a positive effect. In a hierarchical dependence model, the combined effect of cormorant predation on fish was negative, but the overall effect was not significant at the 95% confidence level (−0.169, 95% C.L. −0.505 to 0.167, p = .256, df = 5.26). A covariate analysis revealed a difference in predatory effects between fish prey taxa (p = .006, df = 5.73), but no difference in effect sizes between study type, foraging habitat, or response variable measured. The meta-analysis reveals a complex interaction between cormorants and fish, but adds to the consensus on the importance of considering cormorant predatory effects in research, conservation actions, ecosystem-based management, and environmental monitoring.

Overexploitation of fisheries is recognized as a major environmental and socioeconomic problem that threats biodiversity and ecosystem functioning. Inappropriate management policies of fish stocks have been applied as a consequence of inadequate characterization of subtle genetic structure in many fish species. In this study, we aim to assess the extent of genetic differentiation and structure of vendace (Coregonus albula) collected from eight locations in the Bothnian Bay, the northernmost part of the Baltic Sea. Specifically, we test if this species forms a single panmictic population or is divided into several genetically distinct units. We used restriction site-associated DNA sequencing (RAD-seq) to identify 21,792 SNPs based on 266 individuals. We identified a clear pattern of genetic differentiation between River Kalix and the other sampling locations, and a weak structuring between samples from Swedish and Finnish coast. Outlier analysis detected 41 SNPs putatively under divergent selection, mainly reflecting the divergence between River Kalix and the other samples. The outlier SNPs were located within or near 25 genes, including voltage-dependent calcium channel subunit alpha-2 (CACNA2D2), cadherin 26 (CDH26) and carbonic anhydrase 4-like (CA4) that have earlier been associated with salt-tolerance and salinity stress. Our study provides the first genome-wide perspective on genetic structuring of Baltic Sea vendace and rejects the hypothesis of panmixia in the Bothnian Bay. As such, our work demonstrates the power of RAD-sequencing to detect low but significant genetic structuring relevant for fisheries management.