Varying back-calculated growth in Atlantic herring (Clupea harengus) along the Norwegian coast based on scales and otoliths

Abstract

Atlantic herring display a wide spatial distribution where its numerous populations encounter various environmental factors and selective forces, thus having different prerequisites for growth. This report aims to provide insight to Atlantic herring growth along the Norwegian coast, using back-calculated length-at-age derived from annual growth measurements of scales and otoliths. It incorporates genetically assigned individuals to populations, enabling the comparison of growth between and within populations. Three back-calculation models: the Dahl-Lea, the Scale Proportional Hypothesis, and the Body Proportional Hypothesis were independently integrated to the von Bertalanffy growth formula and compared. Further, the potential use of otolith core characteristics was investigated to validate whether these characteristics can serve as markers for assigning individuals as spring or autumn spawners. The length-at-age data derived from the different back-calculations models varied, where the Body Proportional Hypothesis model proved the best model fit. Growth estimates from scales and otoliths provided varying results, with otoliths consistently exhibiting higher growth rates compared to scales, and scales generally indicating greater asymptotic length compared to otoliths. This research found variances in Atlantic herring growth, both between and within populations. NSAS herring displayed higher growth rates compared to NSS herring, while NSS herring exhibited greater maximum lengths compared to NSAS herring. NSS herring in Sunnmøre demonstrated young and small individuals, indicating a potential nursery area. The core classification proved discrepancies from the genetic data and imply that genetic classification is necessary to accurately assign an individual as a spring or autumn spawner. This research underlines the high level of phenotypic plasticity in Atlantic herring, exhibiting differences in growth in relation to populations, spatial occupancy, calcified structures, and choice of models.