© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Size at maturity of the smallnose fanskate Sympterygia bonapartii (Müller & Henle, 1841) (Pisces, Elasmobranchii, Rajidae) in the SW Atlantic
a Dirección Nacional de Recursos Acuáticos, Departamento de Biología Pesquera Constituyente 1497, C. P. 11200 – PO Box 1612, Montevideo, Uruguay
b Departamento de Oceanografia, Fundação Universidade Federal do Rio Grande Caixa Postal 474, CEP 96201-900, Rio Grande–RS, Brazil
*Correspondence to M. C. Oddone: Departamento de Oceanografia, Fundação Universidade Federal do Rio Grande, Caixa Postal 474, CEP 96201-900, Rio Grande–RS, Brazil; tel: +55 53 2336526; fax: +55 53 2336601. e-mail: pgobmco{at}furg.br.
The smallnose fanskate Sympterygia bonapartii is found in coastal and shelf waters between southern Brazil and southern Argentina. Since 1994 it has become an alternative and commercially important target of demersal fisheries. In Uruguayan waters, the onset of sexual maturity in the species is at 65.5 cm for females and at 50–57 cm for males.
Keywords: size at maturity, smallnose fanskate, sub-tropical, Sympterygia
Received 25 July 2003; accepted 19 November 2003.
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1 Introduction |
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 Top 1 Introduction 2 Material and methods3 Results and discussionReferences |
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The smallnose fanskate Sympterygia bonapartii (Müller & Henle) is found from Rio Grande do Sul in southern Brazil to southern Argentina (Figueiredo, 1977). It is considered a coastal and intermediate shelf species (Cousseau and Perrotta, 2000), occurring down to 150 m (Paesch et al., 1995). Along with other skates and demersal sharks, it is a common by-catch in the coastal and continental shelf bottom-trawl fisheries of the Argentine–Uruguayan Common Fishing Zone, ZCPAU (34°30'–39°30'S; Figure 1; Ehrhardt et al., 1977; Paesch and Meneses, 1999). Since 1994, it has been fished extensively by bottom trawl and bottom longline (Meneses and Paesch, 1999).
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2 Material and methods |
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Top1 Introduction2 Material and methods3 Results and discussionReferences |
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Data for the analyses were obtained during seven cruises carried out between spring 1994 and autumn 1998 on board the RV "Aldebarán" (operated by DINARA, Uruguay), designed to help assess demersal fishery resources in the ZCPAU. In all, 436 female and 123 male Sympterygia bonapartii were analysed. Total length, sex, clasper length (males), and the presence or absence of yellow ovarian follicles and egg capsules in uteri (females) were recorded. Clasper length was measured sensu Compagno (1984), from the point of insertion to the distal end. Females were considered mature when yellow ovarian follicles and/or egg capsules were present. Total length at first maturity (ML) of females was estimated using cumulative frequencies. A logistic model was fitted to the binomial maturity data (immature = 0, mature = 1):
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1, and 2 are parameters (Restrepo and Watson, 1991). The average size at ML was obtained from the relationship
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| (2) |
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3 Results and discussion |
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Top1 Introduction2 Material and methods3 Results and discussionReferences |
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Females ranged in size from 30 to 79 cm total length (TL). The smallest mature female was 43 cm TL and the largest immature female was 73 cm TL. The onset of sexual maturity was calculated to lie at a TL of 65.5 cm (r=0.99; Figure 2). De Queiroz (1986) estimated the value to be 70 cm for female smallnose fanskate off southern Brazil, and Mabragaña et al. (2002) reported it as 64 cm for Argentine waters.
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The size range of males examined ranged from 41 to 78 cm. There is a three-phased sigmoid relationship between clasper length and TL in skates (Capapé, 1974; Capapé and Quignard, 1974; Templeman, 1987), the middle phase of the sigmoid representing maturing fish. According to the data plotted in Figure 3, this phase for smallnose fanskate is at a TL of 52–57 cm; most males >57 cm had well-developed claspers. De Queiroz (1986) reported that males first matured at 52 cm, but Mabragaña et al. (2002) estimated the same value to be 65 cm. However, the latter calculation may well have been in error because female skates generally mature at a larger size than males (e.g. Jardas, 1973; Nottage and Perkins, 1983; Fuentealba and Leible, 1990; Walker, 1999; Walmsley-Hart et al., 1999; Oddone 2003). Although there may well be natural variations among populations, estimation of size at maturity can be affected by the use of different methodologies to measure claspers. Mabragaña et al. (2002), unlike De Queiroz (1986), measured the claspers from the tip of the pelvic fin to the tip of the clasper. This would mean that, in fish with claspers shorter than the pelvic fin, clasper length would be negative. That method differs from the method used for this analysis and recommended by Compagno (1984), so it may well be the cause of the different sizes at maturity in the literature for the species. Clearly, therefore, comparisons between a species' size at maturity documented by different authors have to be viewed with caution unless the same methodology was applied.
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Acknowledgements |
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We thank Jim Ellis and an anonymous reviewer for their reviews of the submitted manuscript.
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References |
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Top1 Introduction2 Material and methods3 Results and discussionReferences |
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