How old is a cod? Age validation studies on wild Baltic cod

Project

Ein mit Tetracyclin makierter Dorschotolith im Querschnitt (c) Thuenen-Institut/Aisha Degen-Smyrek
Ein mit Tetracyclin makierter Dorschotolith im Querschnitt (© Thuenen-Institut/Aisha Degen-Smyrek)

DCF (Data Collection Framework): Age validation studies on Baltic cod using marked otoliths

We would like to know the age of a cod as precisely as possible. Since cod do not swim around with an identification card, we have to use the partly imprecise interpretation of ring structures in their ear stones (otoliths). To verify the relationship between structures in ring formation and true fish age, we carry out age validation experiments using wild Baltic cod.

Background and Objective

Age validation is a central pillar for the understanding of the biology of fish stocks. Presently, the age determination of Baltic cod is subject to significant levels of uncertainty despite numerous efforts in the past. Accordingly, the predictions of the stock assessment are uncertain.

Therefore, we initiated a catch-release experiment that in an early phase is conducted mainly on a national level. Thereby we want to validate the age of cod. We analyse the ring structures the fish has produced between release and recapture. Thus, in the future we may be able to assign the true age to the ring structure of otoliths from non-marked cod.

Approach

In a pilot study we identified tetracycline as the most appropriate chemical to mark the otoliths for an age validation study. We are catching live cod to mark them internally (with tetracycline as a time tag inside the otoliths) and externally (with a numbered so-called spaghetti tag for the detection by fishers and anglers upon recapture). Then we hope and wait that marked cod are recaptured and returned as whole fish for further analysis. A reward is paid for each recaptured cod when the whole individual fish is returned.In a pilot study we identified tetracycline as the most appropriate chemical to mark the otoliths for an age validation study. We are catching live cod to mark them internally (with tetracycline as a time tag inside the otoliths) and externally (with a numbered so-called spaghetti tag for the detection by fishers and anglers upon recapture). Then we hope and wait that marked cod are recaptured and returned as whole fish for further analysis. A reward is paid for each recaptured cod when the whole individual fish is returned. 

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Involved Thünen-Partners


Duration

9.2013 - 12.2019

More Information

Projekt type:
Project status: ongoing

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