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Revista de biología marina y oceanografía

On-line version ISSN 0718-1957

Rev. biol. mar. oceanogr. vol.42 no.1 Valparaíso Apr. 2007

http://dx.doi.org/10.4067/S0718-19572007000100001 

 

Revista de Biología Marina y Oceanografía 42(1): 1-5, abril de 2007

ARTÍCULOS

Estimation of body size using morphometric relationships of head bones, pectoral fin bones and bony precaudal distance in Raneya brasiliensis (Kaup, 1856) (Pisces, Ophidiiformes, Ophidiidae) in Patagonian waters

Estimación de la talla utilizando relaciones morfométricas de huesos del cráneo, de la cintura escapular y de la distancia precaudal ósea en Raneya brasiliensis (Kaup, 1856) (Pisces, Ophidiiformes, Ophidiidae) de aguas patagónicas

 

Atila E. Gosztonyi1, Luisa Kuba1 and Lidia E. Mansur1

1Centro Nacional Patagónico. Bvd. Brown s/n. (9120) Puerto Madryn, Chubut, Argentina
goszto@cenpat.edu.ar


RESUMEN

El ofídido Raneya brasiliensis (Kaup, 1856) es una especie clave en las cadenas tróficas de alto nivel del Atlántico sudoccidental. Se calcularon ecuaciones de regresión predictivas, para estimar la talla a partir del tamaño de huesos del cráneo, del cráneo, la cintura escapular y de la distancia precaudal ósea. La transformación logarítmica de las medidas originales dio los mejores ajustes para las estimaciones.

Palabras clave: Piscivoría, mamíferos marinos, aves marinas, patagonia Argentina


ABSTRACT

The ophidiid fish Raneya brasiliensis (Kaup, 1856), is a key link in the Southwestern Patagonian higher level food web. Predictive regression equations were calculated to estimate total length in this species, using head length, various head bone lengths, cleithrum length and bony precaudal length as the independent variables. Log-transformed data gave the best fits in the equations obtained.

Key words: Piscivory, marine mammals, marine birds, Argentine Patagonia


INTRODUCTION

Raneya brasiliensis is a widely distributed ophidiid fish, living in coastal waters, at depths of 40 to 150 m, in the southwestern Atlantic, from Southern Brazil, about 23°S (Carvalho Filho 1999) to South Central Patagonia, around 46°S. Although commercially unimportant, R. brasiliensis constitutes a key link in the food web of the South Atlantic Ocean. As an important prey item in the diet of marine mammals, marine birds and fishes, it was found as food of the southern sea lion Otaria flavescens (Shaw, 1800) by Koen Alonso et al. (2000), of the imperial cormorant Phalacrocorax atriceps King, 1828 by Malacalza et al. (1994) and Gosztonyi & Kuba (1998), of the black–necked cormorant Phalacrocorax magellanicus Gmelin, 1789 by Libenson (1996). Also, R. brasiliensis appeared in the diet of the spiny dogfish, Squalus acanthias Linné, 1758 (Koen Alonso et al. 2002) and the skate Dipturus chilensis (Philippi, 1892) (Koen Alonso et al. 2001). Felisa Sánchez1 reports its presence under the older name Raneya fluminensis, as food in a variety of elasmobranchs Callorhinchus callorhynchus (Linné, 1758), Squalus acanthias, Squalus mitsukurii Jordan & Snyder, 1903, Atlantoraja castelnaui (Miranda Ribeiro, 1907), Bathyraja brachyurops (Günther, 1880), Dipturus flavirostris and Sympterygia bonapartei (Müller & Henle, 1841), as well as in the bony fishes Dissostichus eleginoides (Smitt, 1898) and Genypterus sp.

In order to help in the assessment of the quantitative contribution of R. brasiliensis to the diet of marine organisms, predictive regression equations of skull length, skull and pectoral girdle bones’ size, and the bony precaudal length against total length were calculated.

 

MATERIAL AND METHODS

Sixty specimens of Raneya brasiliensis, 131 to 303 mm in total length, obtained between October 1980 and December 1998, by bottom trawling, in the vicinity of Isla Escondida (43°43'S; 65°20'W) off Chubut Province, Argentina, at depths of 40 to 55 m, were studied (Fig. 1). The specimens, fixed in 10% formaldehyde solution and preserved in 70 ethanol, were dissected, exposing the vertebral column from the left side, and excising one of the hemichrania (suspensorium, and branchial basket) and the pectoral girdles. In situ staining with alizarin red solution was performed, in order to facilitate the dissections, and preserving the integrity of the bones.

Figure 1. Distribution of Raneya brasiliensis in the Southwestern Atlantic Ocean (in black). The arrow indicates
the sampling area
Figura 1. Distribución de Raneya brasiliensis en el Océano Atlántico Sudoccidental indicada en negro. La flecha indica la zona de recolección de los ejemplares estudiados

 

The bones selected for measurements were those usually appearing in stomach contents of piscivorous organisms and are diagnostic for the species, according to Gosztonyi & Kuba (1996). Measurements were taken with electronic calipers to the nearest 0.l mm according to the schemes delineated in Figs. 2 and 3 respectively. The abbreviations used are the following: VomCaud: vomero–caudal distance or bony precaudal distance, taken from the tip of the vomer to the anterior end of the first caudal vertebra (the first vertebra with a closed haemal arch); Skull: from the tip of vomer to the end of the basioccipital. Op: length of opercular. MxL: length of the maxillary; PmxL: horizontal length of the premaxillary; PmxH: height of the ascending process of the premaxillary; HyomH height of the hyomandibular; HyomL length of hyomandibular; PreopL: length of preopercular; CleiL: length of cleithrum; DenL: length of the dentary.

Figure 2. Schematic view of the general measurements registered
Figura 2. Esquema de las mediciones generales registradas

 

Figure 3. Schematic view of measurements on bones. A: premaxillary; B: dentary; C: maxillary; D: hyomandibular; E: preopercular; F: opercular; G: cleithrum. Scale bar= 5 mm. Abbreviations in text
Figura 3. Esquema de las mediciones de los huesos. A: premaxillar; B: dentario; C: maxilar; D: hiomandibular; E: preopercular; F: opercular; G: cleitro. Barra de escalar= 5 mm. Abreviaturas en el texto

 

All measurements are standard ones except the “vomero caudal distance” (VomCaud), which we consider useful one, when the ingested fishes are partly digested, and the premaxillaries are lacking making them unsuited for total length measurement.

The normality of all the variables was proven with the Kolmogorov-Smirnov-test (as used by Watkinson & Gillis 2003)

The predictive regression equations were calculated using STATISTICA 6.0 with and without logarithmic transformations.

 

RESULTS

Regressions of log-transformed data fitted well in most cases and the corresponding equations obtained are listed in Table 1.

Table 1. Parameters of log-transformed data predictive regression equations of skull bones, pectoral girdle bones and vomero-caudal distance against total length in Raneya brasiliensis. (Log Y= a+ b(Log X))
Tabla 1. Parámetros de las ecuaciones de regresiones predictivas de datos log-transformados de medidas del cráneo, de huesos del cráneo, de huesos de la cintura escapular y de la distancia vomero-caudal vs la longitud total en Raneya brasiliensis. (Log Y= a+ b(Log X))

 

DISCUSSION

The knowledge of individual lengths and weights of prey items in gut contents of piscivores is of great importance, not only to estimate the ingested biomass, but also to establish the length groups the predators are preying upon.

A direct way to quantify the ingested food is weighing the specimens contained in the stomachs of predators. This procedure can be rarely applied, due to the state of the ingested specimens, usually more or less digested, and unsuited for proper measurement. Another, and often–used procedure, is back calculating the length of the prey item using regression equations of body length (or body weight) vs otolith lengths. The latter technique has its drawbacks since otoliths are not only eroded by digestive fluids, negatively biasing the estimated lengths or weights, but also show great ontogenetic variations (see e. g. North et al. 1984) making both identifications and measurements uncertain. The limitations of using otoliths in quantitative feeding studies have been thoroughly analyzed by Jobling & Breiby (1986).

An alternative method is to use the dimensions (length or height) of skeletal elements of the preys as independent variables in the length or mass estimations. For examples, see Armstrong & Stewart (1996), Hansel et al. (1988) and Scharf et al. (1997). This procedure has advantages over the one using otoliths since: a) bones are often more reliable than otoliths in order to identify the fish they come from, especially when the otoliths are worn by digestion or when they come from juvenile specimens and, b) the errors in the length estimations are smaller, due to the larger size and hence the smaller relative error of the independent variable.

With these thoughts in mind, we decided to explore the possibility of using skull and pectoral girdle bones and specific body part measurements, to back calculate the body length of R. brasiliensis. As can be seen in Table 1, the regression equations obtained seem to be statistically appropriate for use. In combination with published length/mass relationships e.g. Muto et al. (2000), they can be used to estimate both the length and the mass of the ingested fishes.

Since most of the predators of R. brasiliensis, and, very specially, the marine mammals and birds, belong to the highest trophic levels, its relevance in the food chains of Patagonian waters is obvious, and we hope that the results of this research will help to better understand and eventually manage the whole ecosystem.

 

ACKNOWLEDGMENTS

We wish to express our gratitude to Lic. Ricardo Fondacaro, from Rawson, Argentina and Prof. Juan Carlos Berón, Puerto Madryn, Argentina, for collecting and donating the specimens, and to Mr. Mateo Cornejo for computational assistance. We also acknowledge the helpful criticism and suggestions of the referees.

 

NOTES

1. Felisa Sánchez. National Institute of Fisheries Research and Development, Mar del Plata, Argentina

 

LITERATURE CITED

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