New publication: Response to comments by Cardinale et al. on “Local cod (Gadus morhua) revealed by egg surveys and population genetic analysis after longstanding depletion on the Swedish Skagerrak coast” by Svedäng et al. (2019)
By Carl André, Julia M. I. Barth, Patrik Jonsson, Sissel Jentoft*, Halvor Knutsen, and Henrik Svedäng in ICES Journal of Marine Science
Cod stocks have declined in many places, so also in the eastern part of Skagerrak (Svedäng and Bardon, 2003; Cardinale et al., 2017). Recently we reported findings of early stage cod eggs on the Swedish coast (Svedäng et al., 2019). The eggs were only a few days old, too young to have been transported from distant spawning areas, thus strongly indicating that they were locally spawned and fertilized. This is of course encouraging news, and also the main result of our study. Using population genetic analysis, we further investigated the possible origin of the cod eggs and found that the cod eggs were genetically differentiated from adult North Sea cod and to a lesser degree also from Kattegat and
Öresund cod, together indicating a possible recovery of a local cod stock on the eastern Skagerrak coast.
Cardinale et al. (2019) question our results, and by reanalysing our genetic data using Bayesian cluster analysis, suggest that the coastal cod eggs represent a mixture of individuals of different origins (i.e. North Sea and Kattegat/Öresund cod stocks) rather
than a separate coastal population.
We agree with Cardinale et al.'s view in that the existence of physically mixed eggs spawned inside the fjord by adults genetically resembling Kattegat/Öresund or North Sea cod cannot be excluded; however, Cardinale et al. have largely overinterpreted our genetic data and results. Their reanalysis of our genotype data is invalid since the statistical method they use is not suitable for detecting a “third local” population with the data at hand. (Continue reading.)
ICES Journal of Marine Science
Published: 04 July 2019
* Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Oslo, Norway.
See the publication webpage for full author information.