Revista de Investigación y Desarrollo Pesquero N° 11 - Abril 1997 REY. INVEST.DES. PESQ. N" 11: 135-144 (1997) DESCRIPTION OF Illex argentinus BEAKS AND ROSTRAL LENGTH RELATIONSIllPS WITH SIZE AND WEIGHT OF SQUIDS * by MARCELA L. IVANOVIC AND NORMA E. BRUNETTI Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), c.c. 175, 7600 Mar del Plata, Argentina. RESUMEN Descripción de las mandíbulas (le lilex argentinus y relaciones del largo rostral con la talla y el peso de los calamares. Se presenta una descripción de las mandíbulas de lIlex argentinus realizada sobre la base de caracteres cuali y cuantitativos. Asimismo se proponen las ecuaciones que representan las relaciones existentes entre el largo del rostro para la reconstrucción de los de cada mandíbula y el largo del manto y peso total de los calamares, como herramienta mIsmos. Un total de 291 ejemplares, abarcando todo el rango de tallas, desde juveniles a adultos, fueron analizados para este propósito. La descripción morfométrica se realizó sobre un total de 90 ejemplares, efectuándose, sobre cada mandíbula, las siguientes mediciones: largo del rostro, largo del capuchón, largo de la cresta, largo del ala y ancho del ala. Los resultados demostraron que las mandíbulas de lIlex argentinus responden al esquema típico de aquellas correspondientes a la familia Ommastrephidae, a la cual pertenece la especie. La mandíbula inferior posee un capuchón amplio, con el rostro y las alas largas, y se caracteriza por la presencia de una estructura notable, denominada diente, sobre la base del ángulo mandibular. La cresta es corta y las paredes laterales moderadamente largas. Fue detectada una notable alometría en el crecimiento del capuchón y la cresta con respecto al rostro. La mandíbula superior también presenta un capuchón amplio, con el rostro largo y curvado y las alas pequeñas; en tanto la cresta y las paredes laterales son largas. El crecimiento del capuchón respecto del rostro es de tipo alométrico, en tanto que el de la cresta es isométrico. La coloración de ambas mandíbulas se intensifica con el crecimiento, especialmente a partir de los 200 mm LM. SUMMARY A description of lIlex argentinus beaks, made on the basis of qualitative and quantitative characteristics, is presented. Likewise the equations that represent the relationships between the rostrallength of each beak with the mantle length and total weight of squids are proposed, as a tool for reconstructing them. A total of 291 squids, comprising the complete size range, from juveniles to adults, were analyzed for the latter purpose. The morphometric description was made on a total of90 individuals, taking the following measurements on each beak: rostrallength, hood length, crest length, wing length and wing width. Results showed that lIlex argentinus beaks present the general scheme of that corresponding to the Ommastrephidae Family, to which this species belongs. The lower beak characteristically has a wide hood, with long rostrum and wings, and a notable knob situated on the basis ofthe mandibular angle. The crest is short and the lateral walls slightly long. * Contribución INIDEP N° 985 135 136 REV. INVEST.DES. PESQ. W 11: 135-144 (1997) A strong growth wide hood, with relation to that Pigmentation of alometry between hood and crest in relation to the rostrum was detected. The upper beak also has a a long curved rostrum and small wings, whereas the crest and lateral walls are long. Hood growth in of the rostrum was detected to be alometric, but that corresponding to the crest was isometric. both beaks intensified with growth, specially from 200 mm ML on. Palabras clave: lllex argentinus, calamar, pico, largo rastra!. Key words: lllex argentinus, argentine shortfinned squid, beak, rostrallength. INTRODUCTION Beaks are the most useful structures for the identification of squid species from the stomach contents of their predators, since the shape and the relative dimensions of the parts that constitute them vary enough between species to allow identification. Thus, many warks have dealt with the description ofthe beaks of species that coexist, determining the morphological and morphometrical characteristics that distinguish each species (Clarke, 1962, 1983,1986; Mangold and Fioroni, 1966; Iverson and Pinkas, 1971; Wolff and Wormuth, 1979; Mercer el al., 1980; Wolff, 1984; PerezGandaras, 1986; Pineda el al., 1996). lllex argentinus is the most abundant and widely distributed squid in the Southwest Atlantic region, where it is the object of a high predation caused by fish, birds and mammals (Clarke el al., 1980; Angelescu and Prenski, 1987; Prenski and Bezzi, 1991; Aguiar dos Santos, 1992; Crespo el al., 1994; Prenski el al., MS). Considering this fact, the necessity of having a description of the species beak arises, as well as the equations that allow the reconstruction 01' the sizes and weights o1'the preyed individuals, 1'rom their mandibules, are required. The only previous work, in this sense, is the key to identi1'y beaks of five species of ommastrephids proposed by Aguiar dos Santos (1992), on the basis 01' qualitative characteristics 01' beaks 1'ound in the stomach contents 01' various predators which inhabit the southern Brazil area. In this wark we present a qualitative and morphometric description 01' the beaks 01' lllex argenlinus and propose the equations to calculate the mantle length and total weight 01' the squids from the rostrallength 01' each beak. MATERIAL S AND METHODS The specimens were gathered during various research cruises carried out on the Argentinian continental shel1' and slope. In total 291 squids, whose sizes varied between 45 and 350 mm mantle length (ML), were sampled to record, besides the mentioned ML, the 1'ollowing data: total weight (TW) in grams, sex and sexual maturity stage (Brunetti, 1990). After extraction 1'rom fue buccal mass, the beaks were immersed for ten minutes in a solution of 50% hypochlorite to remove excess tissue that normally remain stuck, and then washed with abundant water. Finally they were stared in 5% 1'ormalin. The rostrallengths (RL) 01' both beaks were measured 1'or all the individuals to obtain the relationships between them and ML and TW. The criterium ofthe minimum relative mean error between the lineal, potential, exponential and logaritmic models was used to select which ofthem best describes those relationships. A total 01'90 squids, whose sizes ranged between 45 and 285 mm ML, were analyzed far the morphometric description. Five measurements were taken on each beak: hood length (fIL), crest length (CL), wing length (WL), wing width (WW), and the RL mentioned above (Figure 1). These dimensions, excepting WW, were proposed by Clarke (1962, 1986). WW was measured, only on the upper beak, by Wolfr and Wormuth (1979) and Wolff (1984), and it was adapted to the lower beak in this wark. All the measurements were made under binocular microscope, using a graduate ocular, and then trans1'ormed to millimeters. Mean relative ratios between the dimensions o1'the di1'1'erent structures were calculated and utilized to describe the beaks. In arder to detect possible changes associated with growth in the relative size 01'the different structures, fIL, CL, WL and WW were tested, as dependant variables, against RL (independant variable), to determine what regression model ofrered the best adjustment (according to the minimum relative mean error). Finally, Student's t-test 1'or Ha: b = 1 (isometry) was applied in those cases where potential regressions had been 1'ound 0.99). (confidence level ~ IVANOVIC y BRUNETTI: lILE\ ARCiENTLVUS BEA!(S 137 LOWER BEAK UPPER BEAK HOOD FIGURE l. Descriptive seheme 01 the lower and upper beaks 01 Illex argentinus and dimensions measured on them (RL: rastral length, HL: hood length, CL: erest length, WL: Willg lellgth, WW wing width). FIGURA 1. Esquema descriptivo de las estructuras que conforman las mandíbulas inferior y superior de lllex argelltilllls y de las mediciones realizadas sobre ellas (RL: largo rastral, HL: largo del capuchón, CL: largo de la cresta, WL: largo del ala, WW: ancho del ala). RESULTS Beak Description The description of the beaks was made taking into account the general morphology of the total of the squids analyzed. Particular attention to the characteristics used by Wolff (1984) for the identification ofthe beaks of 18 species of cephalopods fram the Pacific Ocean was given. Figure 1 shows the general structure of each beak, as well as the different parts on which the descriptions are based, while Table 1 contains the mean relative ratios between the dimensions taken. Lower Beak The lower beak has a wide hood, its length being 58% of CL on average, with a deep notch in the posterior edge 138 REY. INVEST.DES. PESQ. N' 11: 135-144 (1997) TABLE l. lvfean relative ratios and standard deviations between different dimensions 01 the lower and upper beaks (RL: rostral lellgth. HL: hood length. CL: crest lellgth, WL: willg lellgth, WW: wing width). TABLA l. Indices relativos medios y desviaciones estándar entre las mediciones realizadas en las mandíbulas inferior y superior (RL: largo rostral, HL: largo del capuchón, CL: largo de la cresta, WL: largo del ala, WW: ancho del ala). Ratio RL/RL RL/CL HL/CL WL/WW WL/CL WL/RL WL/RL WW/CL WW/RL mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD (Figure 2). Thc separation between hood and crest, from the lateral view, is noteworthy. The rostrum is relatively long (65% of HL and 37% of CL) and slightly curved. The angle between rostrum and wing is recessed, but, as the squid grows, is partially hidden, seen from the lateral side, by a fold that appears on the superior edge of the wing. On the basis of this angle there is a knob which is gradually included in the shoulder during growth. The crest shows no curvature or fülds and the lateral walls are taller than they are long, without grooves or ridges. The wings are long (82% of CL, 141% ofHL) and wide (39% ofCL). Lower beak Upper beak 0.6534 0.1050 0.3796 0.0426 0.5865 0.0435 0.3085 0.0217 0.2283 0.0158 0.7410 0.0349 2.0997 1.2311 0.2422 0.8264 0.0605 0.1012 0.2388 O.O190 0.3228 0.0280 1.4178 0.1581 2.1954 0.2139 0.3908 0.0539 0.6866 O.1222 1.0516 0.1157 0.1952 0.0213 0.2638 0.0302 shows a moderate curvature (Figure 2). The rostrum is relatively long (30% of HL, 22% of CL) and curved, and the mandibular angle is deeply recesscd. The crcst and thc posterior cdges of the lateral walls are moderately curved. Thc wings are longer than they are wide (123% WL with respect to WW), but relatively short in relation with the rest ofthe mandibular structures, represcnting its length 23% of CL and 32% of HL, while related to RL the values are similar (105%). The wing bases are inserted aproximately on the middle part ofthe anterior edge ofthe lateral walls. Pigmentation Uppcr Beak The upper beak presents a large hood, whose length reaches, on average, 74% of CL. Its upper edge is slightly curved while the lower edge, which continues in the wings, also The process ofpigmentation füllows the same pattern in both beaks. In the juvenil e squids (40-90 mm ML) the only coloured zones are the rostrum, with an intense brown pigmentation, and the anterior part ofthc hood and the superior IVANQV¡C y I3RUNETTl: 1UD: ARGE.I\¡TIJv7JSBEAKS 139 LOWER BEAK ,. '~~ ~:>..' UPPER BEAK ~ .'-"'~- , L_f ~'7' ~ ''''''' ... l \ / =0.5 .¡ ~ cm / L-~, 0.5 cm 0.5 cm ---1 l;icURH 2. Deve/opment and pigmelllaliorl changes of Ihe lower and upper beaks vf 1l/ex argenlinus re1aled lo size. Top: AIL = 139 mm, RL/ower = 1.941 mm, RLupper = 2.510 mm. Cenler: M!~ = 216 mm, RL/ower = 3.576 mm, RLupper = 4.fNI mm. Bottom: ML = 255 mm, RL/ower = 4.320 mm, RLupper = 4,845 mm. FIGURA 2. Cambios de la morfología y pigmentación de las mandíbulas intCrior y superior de lllex argenli1llls producidos durante el crecimiento. Arriba: ML = 139 mm, RLjnferior = 1,941 mm, RLsupcrio1"= 2,510 mm. Centro: ML = 216 mm, IZLjnferior = 3,576 mm, RLsupcri01"= 4,041 mm. Abajo: ML = 255 rnm, RLinferior = 4,320 mm, RLsupcri01"= 4,845 mm. 140 REV. INVEST.DES. PESQ. N" 11: 135-144 (1997) part ofthe wings, which present a light brown colour, with a lighter strip e extending ffom the mandibular angle in each beak (Figurc 2). The rcst ofthe structures: crest, lateral walls, posterior zone of thc hood and lower part of the wings, are completely colourless. Between 100 and 130 mm ML, pigmentation intensifies on both beaks, and the crest and lateral walls ofthe lower beak start to show some colour.The crest of the upper beak starts to be coloured in the size range of 140-180 mm ML, while this process occurs between 190-200 mm ML in the case of the lateral walls. In the lower beak, while the pigmentation ofthe coloured structures progresses, the central zone of the wings starts to be pigmentated in the process described by Clarke (1983) as "spot". The knob starts to be included in the shoulder at about 210-220 mm ML and its pigmentation joins that of the "spot". In the following sizes the pigmentation is darker in both beaks and the colourless stripe on the mandibular angle disappears. There is a colourlcss region in the posterior part ofthc crest and lateral walls, which follows the shape ofthis structures in the lovver beak, but is independent of them in the upper beak. Growth lines can be observed on the lateral walls and wings of the lower bcak, whíle the borders of the wings are translucid. From sizes 230-240 mm ML in males and 250260 mm ML in females, both beaks are totally pigmented, with the only exception ofthe thin transparent borders mentioned abovc. At this stage the colour is brown in almost all the beak, and deep brown, nearly black, in the rostrum, the anterior part ofthe hood and the superior part ofthe wings. Morphometry The relationships between the wing dimensions (WL and WW) and the RL were represented by a lineal model in both beaks, whíle those correponding to HL and CL were bctter described by a potential model (Table 2). The t-tests applied in the latter cases showed that the b values obtained varied signíficantly from 1, for the relationships corresponding to the lower beak. In the upper beak b was significantly different from 1 for the relationship EL/RL, while for CL/RL there were no significant differences. These results show that an alometric growth would take place betwcen the structures involved, which would be stronger in the case of the lower beak. Relationships between the J'ostral mantle length and total weight length with the Rostral lengths of the uppcr beak varied between 0.9 and 7 mm, while in the case ofthe lower beak, they were bctween 0.5 and 6.0 mm (Figure 3). The maximum RL found here possibly correspond to the biggest bcaks of the species, since they were found in females whose sizes were near the maximum (350 mm ML). A lineal model proved to be the best adjustment for the relationship between RL and ML, while for the RL- TW relationship, a potential model was found to be the most adequate (Table 3). TABLE2. Regression equationsfor the relationships between hood length (HL) and crest length (CL) with rostrallength (RL) for both beaks (dimensions in millimeters), and results ofStudent 's t-tests for Ho: b = 1 (confidellce level = 0.99). TABLA2. Ecuaciones de regresión para las relaciones entre el largo del capuchón (EL) y el largo de la cresta (CL) con el largo rostral (RL) de ambas mandíbulas (mediciones realizadas en milímetros), y pruebas t-Student para Ha: b ] (nivel de confianza = 0,99). ~ l::~~~.~ bea!c HL/RL CL/RL Up~r b..~~~..--_..._....__._.........__.. In HL = 0.5825 + 0.8037 In RL r 2 = 0.9714 N=90 In HL = 1.1380 + 1.0413 In RL r 2 = 0.9881 N=90 t=-13.4251 t=3.4158* ** In CL = 1.0676 + 0.8736 In RL r 2 = 0.9855 N=90 In CL = 1.4727 + 1.0067 In RL r 2 = 0.9858 N=90 t = -11.2462** t = 0.5266 ns .~~ IVANOVIC y BRUNETTI: ¡UEX ARGENTINUS BEAKS 141 TABIE 3. Regression equationsfor the relationships between mantle length (ML, in mm) and total weight (Tw, in g) with rostral length (RL, in mm) for both beaks. TABLA3. Ecuaciones de regresión calculadas para las relaciones entre el largo del manto (ML, en mm) y el peso total (TW. en g) con el largo rastral (RL, en mm) para ambas mandíbulas. Upper beak Lower beak ML ML = 24.6648 + 54.1825 RL r 2 = 0.9675 N = 291 ML = 2.0133 + 53.4128 RL r 2 = 0.9635 N = 291 TW In TW = 2.1342 + 2.6311 In RL r 2 = 0.9752 In TW = 0.9559 + 3.2198 In RL r 2 = 0.9745 N = 291 N = 291 LOWER E E UPPER BEAK 400 400 ~300 ~300 ::1 ,D 100 E E ~o~ ~200 ....1 BEAK DD ~200 ....1 ::1 100 ~D o o o 2 3 4 6 5 2 o 4 1000 1000 D 800 D :g 800 ~800 :g 800 ~,~ 400 200 RL (mm) 4 200 5 6 D ~~DDD -- o 3 D oJ.f't;D ~~r 400 o 2 7 6 5 RL (mm) RL (mm) o 3 o 2 3 4 5 6 7 RL (mm) FIGURE3. Relationships between the rostrallengths (RL) of each beak with the mantle length (ML) and total weight (TW) of JIlex argentinus. FIGURA 3. Relaciones entre el largo rastral (RL) de cada mandíbula con el largo del manto (ML) y el peso total (TW) en lllex argentinus. 142 REV. INVEST.DES. PESQ. W 11: 135-144 (1997) DISCUSSION lllex argentinus beaks show the general scheme 01' that corresponding to the Ommastrephidae Family, to which this species belongs, so they can be easily differentiated ffom other squids that are distributed in the same area, specia11y loliginids (Pineda el al., 1996). The identification could be more complcx when other ommastrephid species are involved, such as Martialia hyadesi or Ommastrephes barlramii, whose distributional areas overlap that ofI11ex argentinus in certain zones. The key 1'or the identification 01' beaks 01' five species of ommastrephids, made by Aguiar dos Santos (1992) on the basis 01'beaks 1'ound in the stomach contents of their predators in the southern part 01'Brazil, is highly use1'ul 1'or this purpose. Anyhow, the best way to identi1'y morpho10gica11y similar beaks, is the combined use 01' qualitative characteristics together with some morphometric variables. These variables have produced good results when applied in discriminant analysis techniques, 1'or the identification 01' species ofthe same or difIerent genera (Wolff and Wormuth, 1979; Perez-Gandaras, 1986; Pineda el al., 1996). Mean ratios obtained 1'or the lower beak showed higher variability than those corresponding to the upper beak. This 1'act could be due to two 1'actors: the variability inherent to the process 01' measurement or the morphological changes that take place in the beak. The degree 01'difficulty involved when di1'ferent measurements ofthe lower beak are taken is higher, duc to its shape, than in the upper beak, which would bring a higher error. On the other hand, it was observed that the shape ofboth beaks changes with growth, at least for two of the structures considered in this work, hood and crest, when their lengths are related to the RL. This change is higher in the lower beak, where these relationships showed a strong alometry, while in the upper beak a slight alometry in the relationship HL/RL and isometry for CL/RL were detected. These results reflect what could be perceived intuitively from the direct observation of beaks 01'di1'ferent sizes (Figure 2). While the shape 01' the upper beak remains relatively invariable 1'or a11the sizes, the lower beak of an adult looks different ffom that of a juvenile, specially 1'or the different proportions between hood and crest. Four indices 01' the upper beak obtained in this work were compared with those corresponding to eight species 01' the Ommastrephidae family, showing that the values were similar (Wolff, 1984; Figure 4). The HL/CL index presented the highest differences, with a value lower than the other species. No comparisons of this type were made on the lower beak, since differcnt measurements were taken in both works. Pigmentation changes associated with growth described here are similar to those observed for other ommastrephids (Clarke, 1962; 1980; 1986; Mangold and Fioroni, 1966). Clarke (1962) suggested that the beaks darkening starts to be evident and fast 1'rom the onset ofthe lower beak wings pigmentation, and this is coincidental with the begining of sexual maturation. The process of darkening takes place, in lllex argentinus, at about 200 mm ML, and, at this size, the highest proportiont 01' the squids of both sexes are maturing (maturity stages III-IV), which would indicate that a similar situation to that described by Clarke (1962) also occurs in this species. The models that describe the relationships between the rostrallength of each beak with the mantle length and total weight were calculated with no distinction between sexes, considering that the principal objective was to have a useful tool for the reconstruction of sizes and weights of squids from beaks found in the stomach contents of their predators. Even though there is a high possibility that these relationships difIer between sexes, due to their di1'ferent growth, it would not be useful to have a model for each one, since it is impossible to know if the beaks found in the stomach contents belong to males or females. Mercer el al. (1980), by using morphometric measurements in discrimant analysis, identified the beaks of each sex in lllex illecebrosus, being possible, then, that this fact could be verified also in a related species, such as lllex argentinus. Nevertheless, 1'or the practical use that we pro pose, we believe that the relationships obtained are highly useful. Moreover, these relationships are similar to those proposed by Aguiar dos Santos (1992): Lower beak ML = 5.95 + 60.89 RL In TW = 1.05 + 3.25 In RL Upper beak ML = 3.54 + 51.05 RL In TW ~ 0.91 + 3.03 In RL in the case ofthe upper beak, while those correponding to the lower beak are significantly difIerent. The differences are probably due to the fact that different lower rostral lengths were recorded in both works. RL taken by Aguiar dos Santos (1992) are apparently higher than those presented here, since they were measured including the knob situated in thc base ofthe mandibular angle, as it is showed in the graph presented by the author, whiJe in our case the RL was measured between the rostral tip and the proper angle. Figure 4 al so shows that even though a high variability is presented in the b values corresponding to the lower beak relationships between RL and TW, comparing sixteen species of ommastrephids, for the three lllex species involved the values were similar. IVANOVIC y BRUNETTI: [UEX ARGENTIlv7JS BEAK:; 3.5 143 . 3 . " 8 8. 8........................................................... 8 . 2.5"''''''''''.''''''''''''8''''''''''''''''''''''''''''''''''''''''''''''""""""''''''''''''''.''''''''''''.''''''''''''''''''''''''''''''''''................................................................................................... 2 1.5 u ,,,,,,uu,,,uu,u,,,,,,,,,,,,,,,,,,""''''U''''''U'''''''''U''''''''''''''''''''UU'uuuu,,,,,, "...u 1 uu uu """'U'U'U""''''uuu ".,..", o u..u...uu.uu..u..u.u...u "--",,,"""'"''''hh n 8u uu..u ',,-,,---,-,-,,,'''UUh u u u u uu~ u....... '''''''''''UU'''U'''uuuu''",',,''' ",uU'UU'"''''''U'''U.uuu n o uu..u u ""U'U'" o o 0.5 8 n o o ", o u. o o o n..u '"',,,'-',',,"'-"""'h u.n"""",'nn..',,"''''''-'''--'--'''''''''''''''''''''''''''''''' n,,,--,-,--,-,-,,,,,,,"''''''''...n..-''''""'00"'''''''''''''''''''''''''''''''''''-' ~~~~~~~~~ti. te. I.a. T.e. T.s. T.p. N.s. N.g. N.h. O.b. O.e. D.g. S.O. S.!. O.v. H.p. . b o RUHL . RUCL o HUCL Ó WtN/CL FIGrlRE 4. Comparison ollour mean relative ratios 01 the upper beak and the b values 01 the rostral length/total weight relationships 01 the lower beak 01 sixteen ol1ll1lilstrephid species.- I.i..- Illex illecebrosus, J.c.: [llex coindeti, l.a.: Illex argentinus, Te.: Todaropsis eblanae, Ts.: Todarodes sagiffatus, Tp.: Todarodes pacificus, N.s.: Nototodarus sloani, N.g.: Nototodarus gouldi, N.h.: Nototodarus hawaiiensis, O.b.: Ommastrephes bartramii, D.c.: Ommastrephes caroli, D.g.: Dosidicus gigas, So.: Symplectoteuthis oualaniensis, SI.: Symplectoteuthis luminosa, O.v.: Ornithoteuthis volatilis, H.p.: Hyaloteuthis pelagica. Data taken from WoljJ (1984) and Clarke (1986). (RL: rostrallength, HL: hood length, CL: crest length, WW wing width). FIGURA 4. Comparación de cuatro índices relativos medios calculados para la mandíbula superior y de los valores de b correspondientes a las regresiones entre el peso total y el largo del rostro de la mandíbula inferior entre dieciseis especies de calamares ommastréfidos: Li.: lllex illecebrosus, Lc.: Illex coindeti, La.: Illex argentinus, Te.: Todaropsis eblanae, Ts.: Todarodes sagittatus, Tp.: Todarodes pacificus, N.s.: Nototodarus sloani, N.g.: Nototodarus gouldi, N.h.: Nototodarus hawaiiensis, O.b.: Ommastrephes bartramii, a.c.: Ommastrephes caroli, D.g.: Dosidicus gigas, S.o.: Symplectoteuthis oualaniensis, S.l.: Symplectoteuthis luminosa, O.v.: Ornithoteuthis volatilis, H.p.: Hyaloteuthis pelagica. Datos tomados de Wolff (1984) y Clarke (1986). (RL: largo rostral, HL: largo del capuchón, CL: largo de la cresta, WW: ancho del ala). ACKNOWLEDGMENTS We would like to thank Gabriel Rossi for his assistance during the development of this work as well as Marcela Tobío for the photographic work performed. This contri bution rcpresents a partion ofthe Doctoral Thesis ofMarcela L. Ivanovic in thc Facultad de Ciencias Exactas y Naturales, Uni versidad Nacional de Mar del Plata, Argentina. The research work was carried out during the development ofM.L.L fellowship granted by Consejo Nacional de Investigaciones Científicas y Técnicas (3/93 - 3/95). REFERENCES AGUlAR DOS SANTOS, R. 1992. Relacoes traficas de lllex argentinus (Castellanos, 1960) (Teuthoidea: Ommastrephidae), no sul do Brasil. Magister Thesis. Fundacao Universidade do Rio Grande, 85 pp. ANGELESCU,V. & PRENSKI,L.B. 1987. Ecología trófica de la merluza común del Mar Argentino (Merlucciidae, Merluccius hubbsi). Parte 2. 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