Spatio-temporal overlap of hatching in Norwegian spring-spawning herring and the spring phytoplankton bloom at available spawning substrata

Abstract

Analyses of bottom substrata demonstrated that a potential spawning area of 13 490 nautical miles2 is available for Norwegian spring-spawning (NSS) herring on the Norwegian shelf between 59 and 71°N. However, the availability of suitable substrata differed significantly on a latitudinal scale; 60 of the available spawning area was north of 67°N. However, the spatial distribution of larvae indicated that the bulk of the adult population wintering off northern Norway in the period 19982007 migrated farther south and upstream to spawn. This suggests benefits attributable to extra costs accompanying the spawning migration. To test whether southern spawning is beneficial with regard to overlap between herring larvae and their prey, remotely sensed chlorophyll a data from SeaWiFS were used as a proxy for the onset of phytoplankton bloom (OSB) in discrete bins along the Norwegian coast and linked to interannual variation in the observed average timing of larval hatching during the years 19982007. There was a delay in OSB with increasing latitude of 37 d within the spawning habitat of NSS herring. Overlap between larval hatching and OSB was clearly highest in the south, suggesting that match with prey availability may be an important factor in the selection of spawning grounds by NSS herring. © 2012 International Council for the Exploration of the Sea. Published by Oxford University Press. All rights reserved.