Genetic analysis redraws the management boundaries for the European sprat

Abstract

Sustainable fisheries management requires detailed knowledge of population genetic structure. The European sprat is an important commercial fish distributed from Morocco to the Arctic circle, Baltic, Mediterranean, and Black seas. Prior to 2018, annual catch advice on sprat from the International Council for the Exploration of the Sea (ICES) was based on five putative stocks: (a) North Sea, (b) Kattegat–Skagerrak and Norwegian fjords, (c) Baltic Sea, (d) West of Scotland—southern Celtic Seas, and (e) English Channel. However, there were concerns that the sprat advice on stock size estimates management plan inadequately reflected the underlying biological units. Here, we used ddRAD sequencing to develop 91 SNPs that were thereafter used to genotype approximately 2,500 fish from 40 locations. Three highly distinct and relatively homogenous genetic groups were identified: (a) Norwegian fjords; (b) Northeast Atlantic including the North Sea, Kattegat–Skagerrak, Celtic Sea, and Bay of Biscay; and (c) Baltic Sea. Evidence of genetic admixture and possibly physical mixing was detected in samples collected from the transition zone between the North and Baltic seas, but not between any of the other groups. These results have already been implemented by ICES with the decision to merge the North Sea and the Kattegat–Skagerrak sprat to be assessed as a single unit, thus demonstrating that genetic data can be rapidly absorbed to align harvest regimes and biological units.

Genetic response to human‐induced habitat changes in the marine environment: A century of evolution of European sprat in Landvikvannet, Norway

“…Genetic structure in the 40 reference samples was determined in Quintela et al. (2020), showing three highly distinct and relatively homogenous groups: (a) Norwegian fjords; (b) Baltic Sea; and (c) Northeast Atlantic including the North Sea, Kattegat–Skagerrak, Celtic Sea and Bay of Biscay. Evidence of genetic admixture and possibly physical mixing was detected in the transition zone between the North and Baltic seas, but not elsewhere.…”

“…All 45 samples were genotyped with the 91 SNPs for which protocols are described in their entirety in Quintela et al. (2020). In addition, a subset of 15 of the 45 samples was genotyped with eight microsatellite markers (see Table A1), as described in Glover et al.…”

“…The European sprat is a small pelagic fish that is widely distributed from northern Norway to Morocco, the Baltic Sea, the northern Mediterranean basins, and the Black Sea (Debes et al., 2008). Three geographically distinct genetic groups have been described with nuclear markers: (a) Norwegian fjords, (b) Baltic Sea, and (c) a wide‐ranging component spanning the North Sea, Kattegat–Skagerrak in north to the Celtic Sea, and Bay of Biscay in south (Glover et al., 2011; Limborg, Hanel, et al, 2012; Limborg et al., 2009; Quintela et al., 2020). Furthermore, mitochondrial control region revealed two additional demes in the Mediterranean Sea, Gulf of Lyon, and Adriatic Sea (Debes et al., 2008).…”

“…Furthermore, mitochondrial control region revealed two additional demes in the Mediterranean Sea, Gulf of Lyon, and Adriatic Sea (Debes et al., 2008). Differences found in candidate loci for divergent selection between the fresh‐ to brackish water Baltic Sea and fully marine populations suggest that local adaptation to low salinity is likely (Quintela et al., 2020), as has been shown in other Clupeid species such as the Atlantic herring in the Baltic Sea (Guo et al., 2016; Limborg, Helyar, et al, 2012), and the European anchovy ( Engraulis encrasicolus Linnaeus, 1758) in the Adriatic (Ruggeri et al., 2016) and Tyrrhenian Seas (Catanese et al., 2017). The colonization of Landvik's brackish waters might have been possible due to the sprat's standing genetic variation allowing adaptation to a range of salinities, as conditions in Landvik partly resemble those in the Baltic Sea, the largest brackish water body in the world (Florian Berg, 2018).…”

“…To test for local adaptation and parallel evolution, we first characterized Landvik sprat with a suite of recently developed SNP markers and investigated the origin and connectivity of the lake population using a set of 42 geographically explicit samples, most of which were described in Quintela et al. (2020). Secondly, we investigated whether loci putatively under selection could be identified across these samples.…”