FISHERY BULLETIN: VOL. 75, NO. 4 



1954 1955 1956 1957 1958 1959 I960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 



FIGURE 3. — Christmas Island temperature, 1954-73: A. Fitted curve with a 3-mo resolution (n = 1-80). B. Long-term variation 

 (n = 1-19). C. Short-term variation (n = 20-80). D. Residual variation (n = 21-39, 41-59, 61-79). 



when variations of <3 mo need not be resolved, 

 it is simple to display short-term changes by 

 evaluating the higher harmonics in Equation (2) 

 beginning with the annual sinusoid (n = 18-72 

 for Koko Head, n = 20-80 for Christmas Island). 

 The resulting curves are shown in panels C of 

 Figures 1, 2, and 3. 



The Koko Head temperature curve looks sim- 

 ilar to the initial harmonic fit (Figure 1A) because 

 the long-term changes are small in comparison 

 to the annual variations. In the case of the Koko 

 Head salinity and the Christmas Island tempera- 

 ture, the annual variations that during some 



772 



years were obscured by the long-term trends are 

 clearly apparent. At Koko Head low salinities 

 occur during spring and summer and high salini- 

 ties during fall and winter. At Christmas Island 

 high temperatures occur in late spring and low 

 temperatures in fall or winter. 



Annual Sinusoid and Its Harmonics 



Evaluation of the annual sinusoid and its har- 

 monics yields the mean annual variation. For 

 annual analyses the harmonics n =1,2, 3, and 4 

 have periods of 12, 6, 4, and 3 mo. For the 18-yr 



