Deterministic signals in Norwegian cod records

The nodal tide (Mn) of 18.613 year period, and the solar cycle (Sc) of 10-11 year period, introduce important signals into many geophysical, meteorological, and biological time series. These signals are non-stationary with variable amplitude and phase, features which give rise to complex temporal and geographical patterns. Historical records of Norwegian cod catches were taken from Aarsberetning Vedkommende Norges Fiskerier (1885 to 1931) and from Sætersdal and Hylen (1964) for 1872 to 1951. We present results of maximum entropy spectral analysis (MESA), and describe the contributions of the M„ and Sc signals to these records through an examination of their time domain wavetrains. The main results are as follows. Data from northern Norwegian recording districts (except Finnmark) reveal a strong M„ signal, but no sign of Sc. Data from southern districts show both signals, and. in addition, the Mn signal here provides evidence of a phase shift following maximum lunar déclination in 1917. A weak third signal has the same period as the 8.85 year tide dependent on the longitude of perigee of the lunar orbit. The lunar waves in extreme northern and southern districts are in phase during the years dealt with here, but approximately 180° out of phase or of mixed phase in the intermediate region.