Abstract

Fish otoliths' chronometric properties make them useful for age and growth rate estimation in fisheries management. For the Eastern Baltic Sea cod stock (Gadus morhua), unclear seasonal growth zones in otoliths have resulted in unreliable age and growth information. Here, a new age estimation method based on seasonal patterns in trace elemental otolith incorporation was tested for the first time and compared with the traditional method of visually counting growth zones, using otoliths from the Baltic and North seas. Various trace elemental ratios, linked to fish metabolic activity (higher in summer) or external environment (migration to colder, deeper habitats with higher salinity in winter), were tested for age estimation based on assessing their seasonal variations in concentration. Mg:Ca and P:Ca, both proxies for growth and metabolic activity, showed greatest seasonality and therefore have the best potential to be used as chemical clocks. Otolith image readability was significantly lower in the Baltic than in the North Sea. The chemical (novel) method had an overall greater precision and percentage agreement among readers (11.2%, 74.0%) than the visual (traditional) method (23.1%, 51.0%). Visual readers generally selected more highly contrasting zones as annuli whereas the chemical readers identified brighter regions within the first two annuli and darker zones thereafter. Visual estimates produced significantly higher, more variable ages than did the chemical ones. Based on the analyses in our study, we suggest that otolith microchemistry is a promising alternative ageing method for fish populations difficult to age, such as the Eastern Baltic cod.

Keywords

age estimation; Baltic Sea; Gadus morhua; LA-ICP-MS; otolith chemistry; seasonal patterns

Published in

Journal of Fish Biology
2020, Volume: 97, number: 2, pages: 552-565

SLU Authors

• Heimbrand, Yvette

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    

• Limburg, Karin

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    
  • State University of New York College of Environmental Science and Forestry (SUNY-ESF)

• Casini, Michele

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    
  • University of Bologna

• Sjöberg, Rajlie

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    

• Palmén Bratt, Anne-Marie

  • Department of Aquatic Resources (SLU Aqua), Swedish University of Agricultural Sciences
    

Associated SLU-program

Coastal and sea areas


UKÄ Subject classification

Ecology


Publication identifier

DOI: https://doi.org/10.1111/jfb.14422

Permanent link to this page (URI)

https://res.slu.se/id/publ/106479