Otolith growth of herring (Clupea harengus) and sprat (Sprattus sprattus) in the Norwegian fjords

Abstract

Small pelagic fish play an important role in the ecosystem and are an important economical resource. The two most abundant pelagic fish in the Norwegian fjords are herring and sprat. It is documented that offshore sprat and herring are genetically different from coastal populations. For sprat, there is to this day not found any genetic difference in sprat between the fjords. The connectivity between the fjords is still not known. By applying otolith microstructure, it is possible to investigate early growth in sprat and herring. Daily increments set in the otoliths are usually directly correlated with somatic growth, and otolith microstructure is therefore a powerful tool when looking at early growth. It is hypothesised that early otolith growth between the fjords and between species show different growth patterns. This study shows some small variation between year class 2021 and 2020 in Hardangerfjorden, and non-significant difference in otolith growth between the year classes in Sognefjorden. In addition, otolith growth between the fjords were compered, individually for both specie, showed a significant difference with the same growth pattern in the different fjords. When otolith growth between the species were compared it showed different growth trends, indicating that they grow at different rates. Given the small difference between the year classes, but larger difference between the fjords, one could assume that mixing between the fjords are low.