The Code of Long-term Fluctuations of Norwegian Spring spawning herring

Norwegian Spring spawning herring (Cluea harengus) been associated with large fluctuations. The fluctuations of the biomass have been poorly understood and caused problems in biomass management. Better long-term forecasting thus is crucial for an economic and sustainable utilization of the herring biomass. In this investigation time series of the Kola section sea temperature and the biomass of herring have been investigated by a wavelets analysis to identify the source of long-term cycles. The wavelet analysis shows that the Kola section temperature series has dominant cycles correlated to the 18.6 yr lunar nodal tide and harmonic cycles of 18.6/3=6.2, and 3*18.6=55.8 years. The identified dominant temperature cycles in the Kola section temperature series are explained by a deterministic 18.6 yr lunar nodal tide that influences Atlantic inflow to the Barents Sea. The biomass of Norwegian spring spawning herring has adopted a dominant eigen frequency close to stationary 6.2 years temperature cycle. An investigation of long-term dynamics shows that long-term growth is dependent on the biomass eigen frequency and the phase-relation between 6.2 years and the 18.6 years Kola temperature cycles. This phase-relation is slowly changing and introduces periods of biomass growth, reduction and collapse in a cycle period of 55 to 75 years.