Biological and otolith shape data for a parental generation and their subsequent F1-generation of Atlantic/Baltic herring

Atlantic herring, Clupea harengus, have complex population structures and different populations can be found in fully marine, as well as nearly freshwater conditions. Mixing of populations is known, but the extent of connectivity is still unclear. Ripe spring spawning herring were collected in marine (salinity 35, Atlantic) and brackish water (salinity 6, Baltic Sea) conditions. One Atlantic herring female was crossed with one Atlantic and one Baltic male generating an F1-generation consisting of Atlantic purebreds and Atlantic/Baltic hybrids which were incubated and co-reared at two different salinities, 16 and 35 respectively, for three years. The F1-generation was repeatedly sampled for length measurements, vertebral counts and otoliths were also extracted for shape analysis. Atlantic purebreds grew better than Atlantic/Baltic hybrids at salinity 35, but not at salinity 16. In contrast, Atlantic/Baltic hybrids achieved larger size-at-age than the wild caught Baltic parental group. Mean vertebral counts and otolith aspect ratios were higher for Atlantic purebreds than Atlantic/Baltic hybrids, consistent with the parental groups. There were no differences in vertebral counts and otolith aspect ratios between herring with the same genotype but raised in different salinities. A Canonical Analysis of Principal Coordinates was applied to analyze the variation in wavelet coefficients that described otolith shape. The first discriminating axis identified the differences between Atlantic purebreds and Atlantic/Baltic hybrids, while the second axis represented salinity differences. These results demonstrate that otolith shape and vertebral counts have a significant genetic component and are therefore useful for studies on population dynamics and connectivity.