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Losing track of time : causes and solutions for the problematic determination of Baltic cod age

Heimbrand, Yvette (2021). Losing track of time : causes and solutions for the problematic determination of Baltic cod age. Diss. (sammanfattning/summary) Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880
ISBN 978-91-7760-722-9
eISBN 978-91-7760-723-6
[Doctoral thesis]

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Age is a fundamental parameter in biology and fishery science to estimate growth and population parameters. Losing track of time, in the sense of lacking reliable estimates of age and growth creates substantial problems for managing difficult-to-age-species. This thesis explores the use of fish otolith chemistry to improve age determination. Otoliths produce annual growth zones in the form of alternating opaque and translucent rings, corresponding to fast growth in summer and autumn and slow to no growth in winter. For the eastern Baltic cod (EBC), degraded environmental conditions led to a worsening of visual contrast in their otoliths. The EBC served as a model species to test new methods of aging, taking advantage of seasonally driven patterns in otolith chemical constituents. Experiments demonstrated that patterns of physiologically regulated elements significantly improved agreement among untrained chemical readers when compared to experienced readers using standard visual techniques, and that Mg:Ca and P:Ca showed the clearest patterns. Validations demonstrated mechanistic correlation with fish growth, condition, temperature, parasites and proximity to visible winter zones identified by disappearance of daily rings. EBC otoliths from the Stone Age to the present provided historical perspective. Mn:Ca was correlated with hypoxia and water temperature, indicating highest levels in the 2010s. Metabolic status, proxied by Mg:Ca was highest during the 1980s and 1990s, to thereafter decline. Predicted mean length at age by decade showed highest growth in the 1990s and a dramatic decline in the 2010s. The results from this thesis fill crucial knowledge gaps and provide current and historical insights on how EBC biology has changed over time that could improve the management of the threatened population.

Authors/Creators:Heimbrand, Yvette
Title:Losing track of time : causes and solutions for the problematic determination of Baltic cod age
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :2021
Number of Pages:89
Publisher:Department of Aquatic Resources, Swedish University of Agricultural Sciences
Associated Programs and Other Stakeholders:SLU - Environmental assessment > Programme Coastal and sea areas
ISBN for printed version:978-91-7760-722-9
ISBN for electronic version:978-91-7760-723-6
Publication Type:Doctoral thesis
Article category:Other scientific
Version:Published version
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Ecology
Keywords:age validation, Baltic cod, otolith chemistry, Mg:Ca, P:Ca, hypoxia
Permanent URL:
ID Code:23429
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Department of Aquatic Resources
Deposited By: SLUpub Connector
Deposited On:06 May 2021 08:43
Metadata Last Modified:07 May 2021 12:57

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