Otolith structure as indicator of key life history events in Atlantic cod (Gadus morhua)

• Published in: ICES Journal of Marine Science
• Main Author: Irgens, Christian
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2018
• Subjects: Barents Sea; atlantic cod; Gadus morhua
• Online Access: https://hdl.handle.net/1956/18712

Otoliths are remarkable recorders of the individual life history, as they can reflect the growth trajectory and may encapsulate marks related to ontogenetic, physiological and environmental events. Visible and chemical information from otoliths may provide novel insights related to encountered environmental conditions that are difficult, if not impossible, to achieve by other means. However, a prerequisite to accurately elucidate the background of each individual from interpretations of otolith characteristics, is to understand how ultimate-proximate factors influence the otolith formation process as such. Although the biomineralization process of otoliths is indeed linked to physiology and in particular to metabolic expression, both environmental conditions and ontogeny may affect otolith formation. There are still unresolved issues concerning the precise relationship between intrinsic and extrinsic factors, which may have confounding effects when aiming at fundamentally understanding the process of otolith formation. Hence, this may introduce uncertainties to the interpretation of otoliths in terms of the expressed growth rate, opacity pattern, otolith shape and morphology. This also highlights the importance of validation studies on commercial fish species where otolith characteristics are used to determine age and key life history events that may be essential to stock assessment and management. This thesis thus aimed to resolve how two main life history events, i.e. juvenile settlement and initiation of sexual maturation, can impact the otoliths of Atlantic cod (Gadus morhua), combining both field data and experimental studies. I have further evaluated how underlying endogenous and exogenous factors may fluctuate during life history events, and to what extent this may influence otolith growth and shape. Based on extensive sampling of juvenile cod during trawl surveys in the Barents Sea, settlement was found to have a significant effect on the otolith external morphology. Increased formation of lobe ...