Fisheries Research 69 (2004) 371–379

Morphometric relationships of the European spiny lobsterPalinurus elephasfrom northwestern Sardinia

C. Tidua,b,∗, R. Sardaa, M. Pinnac, A. Cannasd, M.F. Melonib, E. Leccab, R. Savarinob

a Centre d’Estudis Avan¸cats de Blanes, Consejo Superior de Investigaciones Cient´ıficas, C.S.I.C.,Carrer d’Acces a la Cala St. Francesc 18, 17300 Blanes, Girona, Spain

b Cooperativa Acquacoltura e Ricerca, Via Brigata Sassari 31, 09045 Quartu Sant’Elena, Cagliari, Sardinia, Italyc Universita degli Studi di Lecce, Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Via Monteroni, 73100 Lecce, Italy

d Centro Italiano Ricerche e Studi sulla Pesca., Via De Gigli d’Oro 21, 00186 Roma, Italy

Received 30 June 2003; received in revised form 7 May 2004; accepted 17 May 2004

Abstract

Two morphometric relationships, carapace length versus total length (CL versus TL), and carapace length versus weight (CLversus W), were estimated for the spiny lobsterPalinurus elephasfished in northwestern Sardinia. The calculations were donefor both sexes and for the years 1998 and 1999. The power functiony = axb was used in both relationships. The first derivatedY/dCL =abCLb−1, whereY is either TL or W was used to study the growth tendency of TL and W in relation to CL. The resultsshowed no interannual differences in the CL versus TL relationship for both sexes. A negative allometry,b < 1, was found formales which was also reflected in their decreasing growth rate of TL in relation to CL. However, this negative allometry wouldn ersusW ea n to CL.C is yearlyu inally, theu ationshipi©

K

dtrait

0

ot have been detected if the functiony= a+ (bx) had been used since it yields only isometric growth. Conversely, the CL vrelationship showed significant interannual differences for both sexes and a general negative allometry,b < 3. This negativ

llometry was more stressed for males in both years which also was reflected in their lower W growth rate in relatioonsequently, for a better estimation of the W from the CL versus W relationship it is recommended to calculate thsing local values, and limiting the application of the calculated regression only to the range of measures employed. Fse of some condition indices in relation to the negative allometry and the interannual variability in the CL versus W rel

s also discussed.2004 Elsevier B.V. All rights reserved.

eywords: Palinurus elephas; Spiny lobster; Morphometric relationships; Northwestern Sardinia

∗ Corresponding author.E-mail address:carlo@ceab.csic.es (C. Tidu).

1. Introduction

The spiny lobsterPalinurus elephasis widespreain the western Mediterranean Sea, from the S

165-7836/$ – see front matter © 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.fishres.2004.06.003

372 C. Tidu et al. / Fisheries Research 69 (2004) 371–379

of Gibraltar to the Island of Rhodes (Ceccaldi andLatrouite, 2000; Moraitopoulou-Kassimati, 1973), andin the western Atlantic, from Cape Bojador (West coastof Africa) to Norway (Hunter, 1999).

AlthoughP. elephasis one of the main economicresources of the small-scale fisheries in Sardinia (Secciet al., 2000), because of its high economic value, nodata exist on the morphometric relationships for thisspecies in this area.

The morphometric relationships most studied forP.elephasare carapace length versus total length (CL ver-sus TL) and carapace length versus weight (CL versusW). These relationships have been reported in the At-lantic for Brittany (Latrouite and Noel, 1997), Corn-wall (only CL versus TL) (Hepper, 1966; Hunter et al.,1996), Irish West coast (Gibson and O’Riordan, 1965,only CL versus TL;Mercer, 1973, cited in Hunter,1999), Scottish Waters (Ansell and Robb, 1977), andSouth Wales (only CL versus TL), (Hunter et al., 1996).While for the Mediterranean Sea onlyCampillo (1982)reported these relationships forP. elephasfished offCorsica.

All the above, authors when studying the relation-ship CL versus TL considered the growth of TL di-rectly proportional, isometric growth, to the growth ofCL using the linear model TL =a + (bCL), in whichb is considered a constant rate of increase. However,as reported byMinos et al., (1995)in nature the con-stant rate of increase of any morphometric character isa specific feature of the differential increase, that it isd

TLc izefa -s ever,T rror,b to befl -q ver-s eightr tri-b ,2 omeb ,2 edbr a-

tionship forP. elephashas been extensively described,factors such as location, food availability and spawn-ing season can also induce variation (Fisher and Pearcy,1988; Le Cren, 1951; Meretsky et al., 2000).

In the present paper, the relationships CL versus TLand CL versus W for female and maleP. elephasaredescribed for the first time in Sardinia, testing the as-sumption of isometry in both relationships. The dif-ferences between females and males and the temporalvariability for each sex of the two relationships are alsotested. Additionally, the growth tendency of TL and Win relation to CL for males and females is analysed.

2. Materials and methods

Spiny lobsters were caught during two fishing sea-sons from May to August in 1998 and 1999 in the areaoff northwestern Sardinia, between the west side ofAsinara Island and Capo Caccia (Fig. 1). In total, 249trammel net samplings were collected during this pe-riod: 90 in 1998 and 159 in 1999, in the depth range

erived from the power functiony = axb, whenb = 1.The knowledge of the relationship CL versus

an be very useful given that the minimum-legal sor P. elephasis usually expressed as TL (Latrouitend Noel, 1997; Secci et al., 2000), because it is conidered an easier and faster measure to take. HowL measurements can bring in some degree of eecause before measuring TL spiny lobsters haveattened and allowed to relax (Hepper, 1966). Conseuently, the length–weight relationship used is CLus W, because it is more accurate. The length–welationship in spiny lobsters is basic when CL disution is derived from the mass caught (Groeneveld000), or when some models are applied to study siological features such as fecundity (DeMartini et al.003). Also the relationship CL versus W is describy the power functiony = axb, in which isometry iseached whenb = 3. Although the length–weight rel

Fig. 1. Sampling area.

C. Tidu et al. / Fisheries Research 69 (2004) 371–379 373

Table 1Features measured and the number of individuals ofPalinurus elephasobtained from 1998 and 1999 surveys

Sex 1998 1999

n CL range (mm) Mean CL (mm) n CL range (mm) Mean CL (mm)

Females 215 44–98.1 67.4 345 38.5–111.2 69.1Males 294 43.6–112.0 70.0 510 31.5–120 71.4

15–140 m, that is very similar to the distribution rangereported forP. elephas: 10–160 m (Holthuis, 1987).The trammel nets used had an outer panel mesh sizeof 22 cm, and an inner panel with a mesh size of 7 cm.

For each spiny lobster caught, while still alive,CL, TL, W, and sex were recorded. CL and TL wererecorded following Hepper’s (Hepper, 1966) method-ology. Prior to measuring TL, spiny lobsters were flat-tened and allowed to relax. These two features weremeasured with an accuracy of 0.1 mm; while the Whas an accuracy of 1 g.

To compare the relationships CL versus TL andCL versus W by sex for each year (inter-sex com-parisons) and to test their temporal variability (intra-sex comparisons), the distributions of CL should nothave statistical differences, and should have the samerange size (Cone, 1989; Minos et al., 1995). There-fore, we usedt-test to check the assumptions of no

and m

inter-sex differences in CL distributions for individualscaught during the same fishing season, and no intra-sex differences in CL distributions for those caughtduring the two fishing seasons. Once these assump-tions have been met, the relationships CL versus TLand CL versus W for females and males were calcu-lated separately for each year using the power functiony = axb. The parameters of the equations were esti-mated by least-square regression following logarithmictransformation.

For each relationship we usedt-test (Zar, 1999) totest, if there was a significant difference betweenb (theslope) and 1 for CL versus TL, and 3 for CL versus W.Afterwards for both relationships,t-test was used forboth inter-sex and intra-sex comparisons of the slopes.When no significant differences were found for theslopes,t-test was used to compare the elevations (Zar,1999).

Fig. 2. Size distributions of female

aleP. elephasfished in 1998 and 1999.

374 C. Tidu et al. / Fisheries Research 69 (2004) 371–379

Fig. 3. Size distributions of the selected female and maleP. elephas.

As for the two morphometric features, CL versusTL and CL versus W, the growth rates were obtainedfrom the power functiony= axb using the first derivatein relation to CL: dY/dCL = abCLb-1, wherea andbare constants andY is either TL or W.

3. Results

3.1. Population structure

Table 1andFig. 2show the characteristics and thesize structure ofP. elephassampled in 1998 and 1999.Although, there were no intra-sex differences in meanCL for spiny lobsters fished in 1998 and 1999, (t-testP > 0.05, calculated after log transformation becauseof the log normal distribution of the data), there wereinter-sex differences in the mean CL for spiny lobsterscaught in the same fishing season in both years (t-testP < 0.05). Additionally, the size ranges showed bothinter-sex and intra-sex differences. Therefore to meetthe assumptions necessary to carry out the comparisons(same CL distributions and same size ranges), the datacorresponding to two individuals were randomly se-lected from every 5 mm CL group, for both sexes andfor each trammel net sampling within the CL size range44–98 mm. This CL interval was preferred because it

Table 2Characteristics of the dataset used to calculate the relationships CLvs. TL and CL vs. W forPalinurus elephascaught off NW Sardinia

Sex n Mean CL (mm) S.E. CL

Females (1998) 152 67.5 ±0.925Males (1998) 195 69.8 ±0.941Females (1999) 204 69.2 ±0.769Males (1999) 270 70.6 ±0.754

was the common CL range found in the two-fishingseasons for both sexes (Table 1). This procedure wasrepeated until obtaining a dataset that neither presentedinter-sex differences nor intra-sex differences in meanCL (t-testP> 0.05,Fig. 3andTable 2). This methodol-ogy was proposed byMinos et al., (1995)to comparebiometric relationships between two species of greymullet.

3.2. Carapace length versus total length

The parameters of the relationships CL versus TLare reported inTable 3. The regression slopes for fe-males were not significantly different from 1 in bothyears; conversely for males, the slopes were signifi-cantly smaller than 1 in both years (Table 3). Therefore,as expected, the slopes in the inter-sex comparisonswere significantly different in both years (Table 4). On

C. Tidu et al. / Fisheries Research 69 (2004) 371–379 375

Table 3Parameters from the equations TL =aCLb, obtained after log transformation of TL and CL

Sex a S.E. (a) b S.E. (b) R2 Departure fromb = 1

Females (1998) 1.037 ±0.06883 1.027 ±0.01638 0.9632 P > 0.05Males (1998) 1.218 ±0.05674 0.9738 ±0.01340 0.9647 P < 0.05Females (1999) 1.182 ±0.04444 0.9927 ±0.01051 0.9779 P > 0.05Males (1999) 1.320 ±0.03393 0.9504 ±0.007993 0.9814 P < 0.05

Table 4Inter-sex and intra-sex comparisons of the parameters of the CL vs. TL relationship

Compared relationships n Degrees of freedom Difference between slopes Difference between elevations

Females (1998)/males (1998) 347 343 t > t0.05,350 = 1.967 –Females (1999)/males (1999) 474 470 t > t0.05,450 = 1.965 –Females (1998)/females (1999) 356 352 t < t0.05,350 = 1.967 t < t0.05,350 = 1.967Males (1998)/males (1999) 465 461 t < t0.05,450 = 1.965 t < t0.05,450 = 1.965

Table 5Parameters from the common equations TL =aCLb after pooling the data of the years 1998 and 1999 for females and males

Sex a S.E. (a) b S.E. (b) R2 Departure fromb = 1

Females 1.114 ±0.03928 1.0090 ±0.009316 0.9707 P > 0.05Males 1.272 ±0.03133 0.9613 ±0.007390 0.9734 P < 0.05

TL and CL are log transformed.

the other hand, the intra-sex comparisons showed thatthere were not significant differences in both slopesand elevations (Table 4). Thus, a common equation forthe 2 years has been obtained for females and males

Fig. 4. Growth rate of total length in relation to the carapace length.

(Table 5). From these two equations the growth rate ofTL in relation to CL was calculated by means of the firstderivate for both sexes. As shown inFig. 4, in femalesthe growth rate of TL in relation to CL was greater

376 C. Tidu et al. / Fisheries Research 69 (2004) 371–379

Table 6Parameters from equation W =aCLb, obtained after log transformation of CL and W

Sex a S.E. (a) b S.E. (b) R2 Departure fromb = 3

Females (1998) −6.915 ±0.2163 2.958 ±0.05148 0.956 P > 0.05Males (1998) −6.533 ±0.1319 2.851 ±0.03116 0.977 P < 0.05Females (1999) −6.031 ±0.1551 2.747 ±0.03670 0.965 P < 0.05Males (1999) −6.072 ±0.1114 2.727 ±0.02624 0.976 P < 0.05

Table 7Inter-sex and intra-sex comparisons of the parameters of the CL vs. W relationship

Compared relationships n Degrees of freedom Difference between slopes Difference between elevations

Females (1998)/males (1998) 347 343 t < t0.05,350 = 1.967 t > t0.05,350 = 1.967Females (1999)/males (1999) 474 470 t < t0.05,450 = 1.965 t > t0.05,450 = 1.965Females (1998)/females (1999) 356 352 t > t0.05,350 = 1.967 –Males (1998)/males (1999) 465 461 t > t0.05,450 = 1.965 –

than males and constant (isometric growth), whilein males a decreasing rate (negative allometry) wasobserved.

3.3. Carapace length versus weight

The parameters of the relationships CL versus W arereported inTable 6. Only the females fished in 1998 pre-sented a slope that was not different from 3. In the otherrelationships, the slopes were significantly smallerthan 3.

ht in re

The inter-sex comparisons showed in both yearsthat there were not significant differences in the slopes,but there were significant differences in the elevations(Table 7).

The intra-sex comparisons showed in both sexes thatthe slopes in 1998 were significantly greater than theslopes obtained in 1999 (Table 7). Therefore, as ex-pected, the growth rate of W in relation to CL for bothsexes was greater in 1998 (Fig. 5). However despitethis variability, the growth rate of W in both years wasgreater in females (Fig. 5).

Fig. 5. Growth rate of weig

lation to the carapace length.

C. Tidu et al. / Fisheries Research 69 (2004) 371–379 377

Table 8Derived TL for CL = 100 mm forPalinurus elephasfished in different regions

Zone Females Males

Range ofCL (mm)

n Derived TL forCL = 100 mm

Range ofCL (mm)

n Derived TL forCL = 100 mm

AtlanticBrittanny (Latrouite and Noel, 1997) 93–148 69 292.1 86–203 65 276.2Cornwall (Hepper, 1966) 99–161 315 312.0 91–182 194 299.1Cornwall (Hunter et al., 1996) 79–180 961 309.4 85–193 502 292.0Irish west coast (Gibson and O’Riordan, 1965) ? 318 300.8 ? 307 288.3Irish west coast (Mercer, 1973) ? 586 302.8 ? 298 286.6Scottish waters (Anesll and Robb, 1977) 70–158 32 304.3 70–170 26 285.1South Wales (Hunter et al., 1996) 113–160 89 329.8 89–182 41 292.8

MediterraneanCorsica (Campillo, 1982) 50–160 278 283.4 45–175 417 269.8NW Sardinia (present study) 44–98 356 317.5 44–98 465 298.6

4. Discussion

An important result found in the present study is thenegative allometry for males in the relationship CL ver-sus TL, reflected in the decreasing-growth rate of TL inrelation to CL (Fig. 4). Therefore forP. elephas, the useof the power functiony = axb is suggested to study therelationship CL versus TL rather than the model thatyields an isometric growth:y = a + bx. Conversely, fe-males have a constant (isometric) and larger TL growthrate than males. These differences in the growth patternexplain why females for the same CL have a larger TLthan males, which is a general common trait in speciesof spiny lobsters. Thus, for an equal carapace size, fe-males have also a greater abdomen, feature which canbe explained by its reproductive functions since it isthe zone of egg attachment.

The derived TL for CL = 100 mm which it is usedto compare the relationships reported for the variousregions (Table 8), showed some degree of variabilityfor both females and males. This variability can be as-cribed to the different ranges of CL used to obtain theserelationships, and also because the TL measures are inpart dependent on the force exerted to flatten the ab-domen, and to the degree of relaxation of the spiny lob-ster (Hepper, 1966; Latrouite and Noel, 1997). On theother hand, this relationship with its interannual stabil-ity, as found in the present study, showed that it couldnot be affected by the environmental factors. However,to confirm this hypothesis a larger temporal series isr

Conversely, the CL versus W relationship shows aninterannual variability for both sexes. These differencescan be due to changes in food availability that have beenfound linked to some physical environmental featuressuch as temperature and salinity (Weatherley and Gill,1987). Food availability in spiny lobsters besides af-fecting the amounts of storage tissues, it is known to af-fect the gonad development and the fecundity (Pollocket al., 1997). On the other hand, the gonad developmentand the onset of the spawning season are also related tothe water temperature and its interannual variations. InP. elephas, Goni et al. (2003)found that gonad matu-ration for both sexes is matched to the water warm-up.

Hence for a better estimation of the W from thelength–weight relationship, we suggest forP. elephasto calculate this relationship yearly due to its interan-nual variability. Nevertheless, it should also be takeninto account the use of local values because the sam-pling area inP. elephasinfluences the diet as a functionof the composition of the benthic community (Goniet al., 2001), and limit the application of the results tothe length range used to calculate the regression param-eters (Dulcic and Kralievic, 1996; Morey et al., 2003).

Despite the interannual variability, the parametersof the relationships CL versus W are, except for themales fished in 1999, within the range of the pa-rameters reported forP. elephasfished in other re-gions (Table 9), in which the main characteristic isthe general negative allometry, (slope <3). The neg-ative allometry also characterizes the relationshipsC cies

equired. L versus W described for the con-generic spe

378 C. Tidu et al. / Fisheries Research 69 (2004) 371–379

Table 9Parameters of the relationship CL vs. W (ln W = ln(a + b) ln CL) reported forPalinurus elephasfished in different regions

Zone Females Males

a b Range of CL (mm) n a b Range of CL (mm) n

AtlanticBritanny (Latrouite and Noel, 1997) −5.952 2.726 94–148 70 −6.645 2.856 86–203 65Irish west Coast (Mercier, 1973) −4.946 2.508 ? 416 −6.876 2.913 ? 217Scotland (Ansell and Robb, 1977) −6.834 2.902 70–158 32 −6.832 2.896 70–170 26

MediterraneanCorsica (Campillo, 1982) −7.013 2.942 50–160 278 −7.131 2.966 45–175 417NW Sardinia 98 (Present study) −6.915 2.958 40–98 152 −6.533 2.851 40–98 195NW Sardinia 99 (Present study) −6.031 2.747 40–98 204 −6.072 2.727 40–98 270

Table 10Parameters of the CL vs. W relationship (ln W = ln(a + b) ln CL) reported for other species of the genusPalinurus

Species Females Males

a b n a b n

P. delagoe(Groeneveld and Goosen, 1996) −6.438 2.795 54 −6.377 2.776 60P. gilchristi (Groeneveld and Goosen, 1996) −6.908 2.944 53 −6.571 2.856 84P. mauritanicus(Minchin, 1989) −6.120 2.750 ? −6.760 2.880 ?

(Table 10) P. delagoaeandP. gilchristi fished off theEast and South coasts of South Africa (Groeneveldand Goosen, 1996), andP. mauritanicusfished off theWest coast of Ireland (Minchin, 1989). However, inall the cases for the same CL size, females are heav-ier than males due to the female’s greater abdominalmuscular mass (Farrugio, 1975). This can also ex-plain, at least forP. elephasfished in NW Sardinia,why in females the growth rate of W in relation toCL is larger than males, in spite of its interannualvariability.

Due to this negative allometry in the genusPal-inurus, the use of the Fulton’s condition factorK =cW/CL3, (c= constant), that assumes isometric growth,could not be appropriate (Cone, 1989; Ricker, 1975).Moreover, the use of the extension of the Fulton’sindex developed byRicker (1975), K = WCL−b, inwhich b is the slope of the length–weight regres-sion, has been found to be unsuitable for the inter-annual comparisons of the condition. The reason isbecause it assumes homogeneous slopes of the sam-ples to be compared, however, this is not the casefor P. elephasfished in northwestern Sardinia becauseof the interannual variability of the slopes for bothsexes.

Acknowledgements

This research was funded by the Italian Ministerodelle Politiche Agricole e Forestali. We thank the fish-ermen from the Cooperativa Pescatori Stintino for theircollaboration. We also acknowledge S. Saba, P. Soli-nas, L. Ligios, O. Sanna, C. Wendelin, M. Bianchini, C.Campillo-Campbell and D. Campbell for their valuablesupport throughout the study. Also the authors wouldlike to express their appreciation for the referees’ com-ments that have contributed to the improvement of thispaper.

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