Two morphometric relationships, carapace length versus total length (CL versus TL), and carapace length versus weight (CL versus W), were estimated for the spiny lobster Palinurus elephas fished in northwestern Sardinia. The calculations were done for both sexes and for the years 1998 and 1999. The power function y = ax b was used in both relationships. The first derivate dY/dCL = abCL b−1 , where Y is either TL or W was used to study the growth tendency of TL and W in relation to CL. The results showed no interannual differences in the CL versus TL relationship for both sexes. A negative allometry, b < 1, was found for males which was also reflected in their decreasing growth rate of TL in relation to CL. However, this negative allometry would not have been detected if the function y = a + (bx) had been used since it yields only isometric growth. Conversely, the CL versus W relationship showed significant interannual differences for both sexes and a general negative allometry, b < 3. This negative allometry was more stressed for males in both years which also was reflected in their lower W growth rate in relation to CL. Consequently, for a better estimation of the W from the CL versus W relationship it is recommended to calculate this yearly using local values, and limiting the application of the calculated regression only to the range of measures employed. Finally, the use of some condition indices in relation to the negative allometry and the interannual variability in the CL versus W relationship is also discussed.

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