Recent evidence of a functionally extirpated ecotype of herring, Clupea harengus (Actinopterygii, Clupeiformes, Clupeidae), in the southern Stockholm Archipelago, Baltic Sea

The fall spawning ecotype of the herring, Clupea harengus Linnaeus, 1758, is considered functionally extirpated in the Baltic Proper. Once the dominant ecotype in fisheries landings of herring, few observations of this sub-population have been presented in the 21 st century. This short communication describes the opportunistic observation of fall spawning herring larvae in the costal Baltic Proper in 2023 ( n = 61) and 2024 ( n = 23). Back-calculated hatch dates indicated that the larvae likely hatched between the months of September and December prior to capture. Warmer water temperatures coincided with hatching extending later in the year. This study highlights the presence of a herring ecotype recently considered largely absent from the Baltic Proper and supports the need for further studies to investigate their current role in the ecosystem and herring fishery.