Morphometric relationships of the European spiny lobster Palinurus elephas from northwestern Sardinia

Abstract

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.

Ontogenetic changes in morphometry of the spiny lobster, Panulirus homarus homarus (Linnaeus, 1758) from southern Indian coast

“…Many previous studies on CL-W relationship have shown negative allometry (b<3) in majority of lobster species (Berry, 1971;Kabli and Kagwade, 1996;Tidu et al, 2004;Al-Marzouqi et al, 2007). The negative allometry obtained in the present study is similar to the result obtained for P. homarus fished in other regions (Heydorn, 1969;Berry, 1971;Al-Marzouqi et al, 2007) except for the Sri Lankan population in which males are heavier compared to females ( Table 2).…”

“…The results obtained in the present study also conform closely with the linear regression calculated for CL-TL relationship for P. homarus distributed off South African (Berry, 1971) and Sri Lankan waters (Jayakody, 1989). Tidu et al (2004) demonstrated negative allometry for males of Panulirus elephas and suggested the use of power function y=ax b a better model than the linear model that yield an isometric growth: y=a+bx. The advantage of using power function to study the CL-TL relationship is that the difference in growth rate between the two sexes could be clearly broughtout.…”

“…The negative allometry obtained in the present study is similar to the result obtained for P. homarus fished in other regions (Heydorn, 1969;Berry, 1971;Al-Marzouqi et al, 2007) except for the Sri Lankan population in which males are heavier compared to females ( Table 2). The proportionality constant for females in the present study (b=2.9) is higher as the abdomen of the females is heavier which is evident from the longer tail length and wider abdomen in females (Berry, 1971, Kagwade, 1987, Tidu et al, 2004, Al-Marzouqi et al, 2007. In majority of spiny lobsters, for an equal carapace length, females are heavier than males especially beyond maturity and thus dimorphism has been related to egg bearing in females (Heydorn, 1969).…”

“…Spider crabs are commonly known to exhibit three ontogenetic phases in their life history (Hartnoll, 1974(Hartnoll, , 1978. Many previous studies have identified such discontinuity in the relative growth rate of crustacean body parts such as first pleopod length and abdomen width in females and leg length in males (Berry, 1971;Hartnoll, 1974Hartnoll, , 1982Tidu et al 2004;Kulmiye et al 2006;Claverie and Smith, 2009). …”

“…All the above authors when studying the relationship of carapace length (CL) vs total length (TL) considered the growth of TL directly proportional (isometric growth) to the growth of CL using the linear model TL = a + (b CL ) in which b is considered at a constant rate of increase. However, Minos et al (1995) and Tidu et al (2004) applied the exponential equation Y= ax b when b=1 to explain the relationship of CL vs TL as they believed that in nature the constant rate of increase of any morphometric character is a specific feature of the differential increase in these two body dimensions. There are no management regulations governing the harvest of spiny lobsters in India, except for the minimum legal size restrictions for export (Radhakrishnan and Manisseri, 2003).…”