Flounder (Platichthys flesus) is a temperate marine fish that is well adapted to the brackish waters of the Baltic
Sea. There are two sympatric flounder populations in the Baltic Sea, pelagic and demersal spawners, which differ
in their spawning habitat and egg characteristics.
Can variation in hydrological regime explain fluctuations in early life stages?
In the present study, pelagic spawning flounder of the
central Baltic Sea was studied. We examined whether variations in hydrological regime can explain fluctuations
in flounder early life stages that have occurred over the past 30 years (1970—2005). Using generalized
additive modeling to explain the abundance of flounder eggs and larvae in a Latvian ichthyoplankton dataset,
we evaluate the hypothesis that the available reproductive volume, defined as the water column with dissolved
oxygen larger than 1 ml/l and salinity between 10.6 and 12 PSU, affects the survival of flounder ichthyoplankton
and determines recruitment success.
Understanding flounder ecology in the Baltic Sea
Both reproductive volume and spawning stock biomass were significant factors determining flounder
ichthyoplankton abundance. Different measures of water temperature did not contribute significantly to the variability
of eggs or larvae. However, recruitment did not correlate to the supply of larvae. The findings presented in
this study on the relationship between flounder reproduction, spawning stock biomass and reproductive volume,
as well as the lack of correlation to recruitment, are valuable for the understanding of flounder ecology in the Baltic
Sea, and for developing the management of the species.
Highlights of the article
- Flounder reproductive volume varies with major saltwater inflows in to the Baltic.
- Statistical models (GAM) linked flounder early life stages to hydrological conditions.
- Abundance of flounder early life stages depends on reproductive volume and SSB.
- The lack of correlation between larval abundance and recruitment is discussed.