Otolith growth across two generations in Atlantic herring (Clupea harengus)
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The Atlantic herring (Clupea harengus) has a wide distribution and a complex metapopulation structure with interactions between the sub-populations. The sub-populations show different adaptations, both genetic and non-genetic, to their environments, and clear differences are found between Atlantic and Baltic herring. Offspring (F1 generation) from Atlantic and Baltic parents (Atlantic purebreds and Atlantic-Baltic hybrids) were co-reared in a common garden experimental set-up. Initially there were three salinity regimes (6 psu, 16 psu and 35 psu), but the 6 psu regime was terminated at larval life stages. Repetitive samples were taken from each group throughout the whole experiment providing a unique collection of sibling samples from larval to adult life stages. Otoliths from all life stages were available for further otolith microstructure analysis and corresponding microstructure analysis was also available from the two parental populations. The Atlantic parental herring were larger than the Baltic parental herring, but the larval otolith increments indicated an opposite trend where the Baltic herring had better larval growth. The F1 larval somatic parameters indicated a trend where the 35 psu group was larger than the 16 psu group, indicating an impact from environmental factors. The adult purebreds were longer than the adult hybrids, which could indicate a genetic impact. An interaction effect including both salinity and genetics as factors was present for the adult weights and for the otolith larval increment widths of both larval and adult life stages. The results from the present study indicate that these traits were affected by both the environment (salinity) and the underlying genetics. These findings are of high importance in sustainable management when characterising herring stocks, but other environmental factors, like temperature,should also be given more attention and included in further research in addition to having a broader genetic baseline for analysis.