Biophysical Factors Controlling Spatiotemporal Variability in Fishes' Early Life History Distribution in the Kattegat Ecosystem

ABSTRACT

The Kattegat Sea acts as a nursery area for several fishes, exhibiting complex ichthyoplankton dynamics influenced by environmental factors and species‐specific traits. We investigated factors influencing spatiotemporal variability in yolk‐sac larvae presence and areal density for three economically and ecologically important fishes: sandeel ( Ammodytes spp.), Atlantic cod ( Gadus morhua ), and common dab ( Limanda limanda ). We used generalized additive models (GAMs) to reveal how species‐specific presence and density patterns varied with space and time for the 2021 year‐classes. Species‐specific patterns can be explained by a combination of biology (spawning time and mode, and egg dispersal characteristics) and physics (physical advection)—but to varying degrees among the species. Dab timing was consistent with that of batch spawners and previously observed spawning time in the Kattegat. Spatial distribution of dab larvae was widespread and consistent with their pelagic egg stage. Although sandeel could not be identified to species, their presence early in the study period was consistent with lesser sandeel ( A. marinus ) spawning time, spawning mode as total spawners and inflow from the Skagerrak. Spatial distribution of sandeel larvae was patchy, consistent with a lower‐dispersal demersal egg stage. Finally, cod showed a peak in probability of occurrence that was inconsistent with their spawning mode as batch spawners. Inflow from the Skagerrak could explain the temporal pattern with peak timing consistent with previously observed spawning time for cod populations in the Skagerrak. It is unclear how much the Kattegat population contributes to the larval cod year‐class here observed. We conclude that the spatiotemporal variations in distribution are driven by an interplay of physical processes (e.g., advection) and species‐specific biological traits (i.e., spawning time and batch vs. total spawners). Evidence of the influence of physical processes affecting the distribution of fish larvae will have implications for spatial management in the area as well as regions beyond the Kattegat.