Sclerochronological approach for the identification of herring growth drivers in the Baltic Sea

Abstract

Long-term datasets developed based on measurements of archived fish otoliths may help in the evaluation of climatic impacts on marine resources. The objective of the present study was to identify the factors that influence interannual variations in the somatic growth rate of herring (Clupea harengus) in the Baltic Sea. This work covers otolith samples collected from commercial catches and during scientific surveys from 1951 to 2017 in the Polish zone of the southern part of the Baltic. Otolith increment widths, which represent changes in fish growth, were analyzed with linear mixed models to investigate different intrinsic and extrinsic sources of fish growth variation. The stock biomass of pelagic species (herring and sprat Sprattus sprattus), sea surface temperature, Baltic Sea Index and land precipitation over the catchment area were considered potential predictors of herring growth. Methods to identify the optimal time window for environmental factors were incorporated in the modeling. Moreover, a wavelet coherence analysis, tests for identification of regime shifts in fish growth and a spatial correlation analysis were applied to the data. The developed multidecadal otolith-based biochronology showed that the growth of Baltic herring is under the strong influence of interspecific competition between herring and sprat, but the biochronology also indicated a high correlation with precipitation patterns over the runoff area and hydrological conditions within the Baltic Sea. A detailed investigation revealed that the relationships between herring growth and abiotic conditions or other ecosystem components can vary over time. The recognized complex ecological effects on herring growth necessitate the application of holistic ecosystem-based approaches for sustainable management and exploitation of small pelagic fish resources.