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Diet Composition and Feeding Habits of the Eyespot Skate, Atlantoraja Cyclophora (Elasmobranchii: Arhynchobatidae), Off Uruguay and Northern Argentina

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Diet Composition and Feeding Habits of the Eyespot Skate, Atlantoraja Cyclophora (Elasmobranchii: Arhynchobatidae), Off Uruguay and Northern Argentina Neotropical Ichthyology, 14(3): e160032, 2016 Journal homepage: www.scielo.br/ni DOI: 10.1590/1982-0224-20160032 Published online: 30 September 2016 (ISSN 1982-0224) Diet composition and feeding habits of the eyespot skate, Atlantoraja cyclophora (Elasmobranchii: Arhynchobatidae), off Uruguay and northern Argentina Santiago A. Barbini1 and Luis O. Lucifora2 The eyespot skate, Atlantoraja cyclophora, is an endemic species from the southwestern Atlantic, occurring from Rio de Janeiro, Brazil, to northern Patagonia, Argentina. The feeding habits of this species, from off Uruguay and north Argentina, were evaluated using a multiple hypothesis modelling approach. In general, the diet was composed mainly of decapod crustaceans, followed by teleost fishes. Molluscs, mysidaceans, amphipods, isopods, lancelets and elasmobranchs were consumed in lower proportion. The consumption of shrimps drecreased with increasing body size of A. cyclophora. On the other hand, the consumption of teleosts increased with body size. Mature individuals preyed more heavily on crabs than immature individuals. Teleosts were consumed more in the south region (34º – 38ºS) and crabs in the north region (38º – 41ºS). Shrimps were eaten more in the warm season than in the cold season. Prey size increased with increasing body size of A. cyclophora, but large individuals also consumed small teleosts and crabs. Atlantoraja cyclophora has demersal-benthic feeding habits, shifts its diet with increasing body size and in response to seasonal and regional changes in prey availability and distribution. La raya de círculos, Atlantoraja cyclophora, es una especie endémica del Atlántico Sudoccidental, que se distribuye desde Río de Janeiro, Brasil, hasta el norte de la Patagonia, Argentina. Los hábitos alimentarios de esta especie fueron evaluados frente a la costa de Uruguay y norte de Argentina, utilizando un enfoque de modelado de múltiples hipótesis. En general, la dieta estuvo compuesta principalmente por crustáceos decápodos (71,37 %IRI), seguido de peces teleósteos (28,54 %IRI). En menor proporción fueron consumidos moluscos, misidáceos, anfípodos, isópodos, anfioxos y elasmobranquios. El consumo de decápodos Natantia disminuyó con el incremento del tamaño del cuerpo de A. cyclophora. Por otro lado, el consumo de teleósteos se incrementó con el incremento del tamaño del cuerpo. Individuos maduros consumieron cangrejos en mayor proporción que individuos inmaduros. Los teleósteos fueron consumidos mayormente en la región sur (34º – 38ºS) y los cangrejos en la región norte (38º – 41ºS). Los decápodos Natantia fueron más consumidos en la estación cálida que en la estación fría. El tamaño de las presas consumidas se incrementó con el aumento del tamaño corporal de A. cyclophora, pero individuos de mayor tamaño no abandonadon el consumo de pequeños cangrejos y teleósteos. Atlantoraja cyclophora presenta hábitos alimentarios demersal-bentónicos, cambia su dieta con el incremento del tamaño corporal y en respuesta a cambios estacionales y regionales en la disponibilidad y distribución de las presas. Keywords: Chondrichthyes, Ontogenetic shifts, Predation, Southwest Atlantic. Introduction ranging from the shoreline to 150 m and it reaches a maximun total length of 695 mm (Cousseau et al., 2007). The eyespot skate, Atlantoraja cyclophora (Regan, Off Uruguay and southern Brazil waters, A. cyclophora 1903), is a member of the family Arhynchobatidae and it matures at 463-485 mm and 528-532 mm total length for is an endemic species from the southwestern Atlantic, male and female, respectively (Oddone & Vooren 2005; occurring from Rio de Janeiro, Brazil (22º S) to northern Oddone et al., 2008). Like other skate species along the Patagonia, Argentina (42º S) (Menni & Stehmann, 2000; coastal and continental shelf waters from north Argentina Bovcon et al., 2011). Typically, this species inhabits depths and Uruguay, A. cyclophora is subjected to heavy fishing 1Laboratorio de Ictiología, Instituto de Investigaciones Marinas y Costeras, Universidad Nacional de Mar del Plata, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Funes 3350, Mar del Plata, B7602AYL, Buenos Aires, Argentina. [email protected] (corresponding author) 2Instituto de Biología Subtropical – Iguazú, Universidad Nacional de Misiones, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Casilla de Correo 9, Puerto Iguazú, N3370AVQ, Misiones, Argentina. [email protected] 1 Neotropical Ichthyology, 14(3): e160032, 2016 2 Diet of Atlantoraja cyclophora pressure in multi-species fisheries for coastal demersal Material and Methods species (Tamini et al., 2006), with a decreasing trend in population abundance (Massa et al., 2006). Like most Study area and sampling. The study area is located off elasmobranchs, A. cycplohora may be particularly sensitive Uruguay and northern Argentina, between 34º S and to fishing pressure, therefore this species is categorized as 41º S (Fig. 1). The northern area is characterized by a vulnerable by the International Union for the Conservation stratified coastal zone influenced by the discharge of the of Nature (IUCN) (Massa et al., 2006). Río de la Plata. On the other hand, the southern area is Indirect effects of a heavy fishing pressure include a homogeneous coastal zone, that comprises an estuarine disruption of trophic interactions through selective removal system, called El Rincón, characterized by the discharge of predator or prey species, removal of competitors and of the Negro and Colorado Rivers and discharges of high species replacement (Stevens et al., 2000; Bornatowaki et salinity waters of the San Matías Gulf (Guerrero & Piola, al., 2014; Navia et al., 2016). Thus, knowledge of potential 1997; Lucas et al., 2005). ecological consequences of declines in the abundance of Samples of A. cyclophora were taken from scientific predators is critical for fisheries and marine ecosystem trawl surveys conducted by the Instituto Nacional de management (Heithaus et al., 2008). For this reason, Investigación y Desarrollo Pesquero (INIDEP, Argentina) information on feeding habits and trophic interactions and from commercial landings of the coastal fleet of Mar between species are very important and necessary ecological del Plata harbour (Fig. 1) during December 2005, February, parameters for the correct management and protection of May, June, September and November 2006, April, May, fisheries (Navia et al., 2016). Despite that, catches of skates July, August, October, November and December 2007. off Argentina increased markedly in recent years (Hozbor & Total length (TL, mm), sex and maturity stage (juvenile Massa, 2012), fishery statistics and ecological traits of these or adult) of each individual were recorded. The maturity species are scarcely known, specially for A. cyclophora. stage was determined according to the presence of eggs From a trophic viewpoint, skates may have an important and observation of the uteri, oviducal glands and ovarian role in structuring marine communities due to their wide follicles in females and to the degree of calcification of the distribution and high abundance (Ebert & Bizzarro, 2007). claspers and the development of testes and reproductive These roles in the marine communities can be influenced ducts in males (Colonello et al., 2011). The stomachs were by traits of the predator (e.g. sex, maturity stage and body removed and stored at -20º C. In the laboratory, prey were size) and extrinsic factors (e.g. season and region) (Di sorted, identified to the lowest possible taxonomic level Giácomo & Perier, 1996; Lucifora, 2003). Therefore, there using published catalogues, counted and wet weight was is a need to investigate the diet of skates with emphasis recorded (± 0.01 g). Whenever possible, carapace width on ontogenetic, seasonal and regional variation. This (CW) of crabs, cephalothorax length (CL) of shrimps and information about life history and trophic interactions total lenght (TL) of teleosts were measured. must be known and incorporated into future analyses, to accurately evaluate the population dynamics (Schmitt et al., 2015). Information on the feeding habits of A. cyclophora is scarce. Diet composition has been studied in detail only off the southern coast of Rio de Janeiro, Brazil, near Ilha Grande, where A. cyclophora preys mainly on crustaceans and teleosts, with seasonal differences in diet composition (Viana & Vianna, 2014). In coastal waters off Uruguay and northern Argentina, the skate species Atlantoraja castelnaui (Miranda Ribeiro, 1907), Rioraja agassizii (Müller & Henle, 1841) and Sympterygia acuta Garman, 1877, that co-occur in space and time with A. cyclophora, showed a consistent regional shift in the diet composition: teleosts were consumed more in the southern part of this region, whereas decapods were eaten more in the northern part (Barbini & Lucifora, 2011; 2012; 2016). Therefore, we expected to find the same spatial pattern in A. cyclophora. We examined the food habits of A. cyclophora off Uruguay and north Argentina. The specific aims of the study were to: (1) describe diet composition; (2) identify Fig. 1. Study area showing the location of trawl stations changes in diet with sex, maturity stage, body size, season (black dots) and cells of the fishing grid (black rectangles) and region; and (3) examine relationships between predator where individuals of Atlantoraja cyclophora were captured size and prey size. off North Argentina and Uruguay. Neotropical Ichthyology, 14(3):
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