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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on June 12, 2007
ICES Journal of Marine Science: Journal du Conseil 2007 64(5):1017-1027; doi:10.1093/icesjms/fsm078
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© 2007 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Feeding ecology and abundance of two sympatric skates, the shortfin sand skate Psammobatis normani McEachran, and the smallthorn sand skate P. rudis Günther (Chondrichthyes, Rajidae), in the southwest Atlantic

Ezequiel Mabragaña1, and Diego A. Giberto2

1 Museo del Mar, Colón 1114, B7600FXR, Mar del Plata, Argentina and Laboratorio de Ictiología, Universidad Nacional de Mar del Plata, Funes 3350, B7602AYL Mar del Plata, Argentina.
2 Laboratorio de Bentos, Instituto Nacional de Investigación y Desarrollo Pesquero, V. Ocampo N° 1, B7602HSA Mar del Plata, Argentina and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina

Correspondence to E. Mabragaña: tel: +54 223 4513553; fax: +54 223 4519779; e-mail: acuarios{at}museodelmar.org

Mabragaña, E., and Giberto, D. A. 2007. Feeding ecology and abundance of two sympatric skates, the shortfin sand skate Psammobatis normani McEachran, and the smallthorn sand skate P. rudis Günther (Chondrichthyes, Rajidae), in the southwest Atlantic. – ICES Journal of Marine Science, 64: 1017–1027.

The diet, feeding strategy, and abundance of Psammobatis normani and P. rudis in the southwest Atlantic was investigated to determine whether the species are segregated by habitat or dietary preference. The two coexist along the Argentine continental shelf, but there are differences in abundance. The most important prey for P. normani were crustaceans (mainly crabs and isopods) and, to a lesser extent, polychaetes, whereas P. rudis fed almost exclusively on crustaceans (mainly isopods, crabs, and gammarids), and fish and polychaetes contributed less to the diet. This suggests that P. normani and P. rudis are secondary consumers (trophic level <4). The two species fed on similar taxa, but in slightly different proportions according to region. However, an ANOSIM test failed to reveal significant differences in their diets. Circumstantial evidence of food competition is suggested, because the two species attain similar adult size and there are no notable morphological differences between them. Interspecific competition may be reduced by the use of distinct feeding behaviour and by the abundance of prey especially along shelf-break fronts. The use of standard ecological indices of similarity and multivariate techniques to calculate dietary overlap is evaluated.

Keywords: Argentine continental shelf, diet composition, dietary overlap, Psammobatis, skates

Received 22 September 2006; accepted 9 May 2007; advance access publication 12 June 2007.


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