Norwegian Sea NOR Norwegian spring-spawning herring acoustic abundance index in Feb-Mar

Acoustic surveys on the spawning grounds of Norwegian spring-spawning herring (NSS) have been carried out from 1988 onwards, with some breaks e.g. in 2001–2004 and 2009–2014. The majority of NSS herring spawns on-banks along the Norwegian coast from Møre (≈62° N) to Vesterålen (≈69° N) in mid-February to mid-March. However, the timing and location of spawning within this area and period have varied between years, e.g. there seems to be a trend towards earlier spawning in more recent years. Numbers at age have been re-estimated with stox for years where it was possible to get data, and these estimates are used as input to the ICES stock assessment of NSS herring.