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Losing track of time

causes and solutions for the problematic determination of Baltic cod age

Heimbrand, Yvette (2018). Losing track of time. Öregrund: (NL, NJ) > Department of Aquatic Resources, Sveriges lantbruksuniversitet. Aqua introductory research essay ; 2018:1

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Cod (Gadus morhua) is a key fish species of the Baltic Sea, economically as well as ecologically. Stocks declined during recent decades due to factors such as high fishing pressure, loss of spawning and feeding habitats caused by eutrophication, changing climate and widespread hypoxia. The growing seal population preys on cod and increased contact has resulted in the transmittance of parasites to cod, causing additional stress. In order to manage fisheries, age distribution and growth history of fish are needed to run stock assessment models. Based on these biological references, decisions are made for fishing quotas and restricting catches. Fish age is usually determined from counting annual growth zones in otoliths, calcium carbonate structures situated in the skull of the fish. Otoliths grow incrementally, depositing layers of material, forming annual rings reflecting growth, like a tree’s rings. Baltic cod otolith readability has always been somewhat difficult; today the poor condition of Baltic cod has worsened the problem. Unclear seasonal growth zones in otoliths have made age data unreliable, resulting in an uncertain forecast for stock size and suspended Marine Stewardship Council (MSC) certificate for sustainable seafood. However, invisible to the eye, the chemistry of the otolith contains a “hidden code” that could validate conventional ageing methods. The otolith takes up trace elements and isotopes from the surrounding water; hence the fish’s seasonal migration among areas with different environmental conditions is recorded in the otolith. Microchemical analyses enable us to track seasonal changes in trace elemental and isotopic composition in the otolith throughout the fish’s life. The aim of this thesis is to (1) explore the potential use of otolith chemistry as an age validating tool, (2) provide alternative ways to age fishes when other methods fail, as well as (3) provide novel information for aquatic monitoring.

Authors/Creators:Heimbrand, Yvette
Title:Losing track of time
Subtitle:causes and solutions for the problematic determination of Baltic cod age
Series Name/Journal:Aqua introductory research essay
Year of publishing :2018
Number of Pages:62
Place of Publication:Öregrund
Publisher:Department of Aquatic Resources, Swedish University of Agricultural Sciences
ISBN for electronic version:978-91-576-9556-7
Publication Type:Report
Article category:Other scientific
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
(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Biochemistry and Molecular Biology
Keywords:age validation, otolith chemistry, Baltic cod, Gadus morhua, LA-ICP-MS, SFXM, seasonal patterns
Permanent URL:
ID Code:16463
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Department of Aquatic Resources
Deposited By: SLUpub Connector
Deposited On:27 Nov 2019 10:01
Metadata Last Modified:27 Nov 2019 10:01

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