Reproductive biology of the eyespot skate Atlantoraja cyclophora (Elasmobranchii: Arhynchobatidae) an endemic species of the Southwestern Atlantic Ocean (34ºS - 42ºS)

Jorge H. Colonello,Anahí Wehitt,Elena J. Galíndez,Gustavo J. Macchi

doi:10.1590/1982-0224-20170098

Abstract

ABSTRACT Atlantoraja cyclophora is an endemic skate to the continental shelf of the Southwestern Atlantic Ocean (22ºS-47ºS) and a by-catch species in commercial bottom trawl fisheries. The morphometric relationships, the size at maturity and the reproductive cycle of this species were analyzed, with samples collected between 34ºS and 42ºS. The size range was 190 to 674 mm total length (TL) for males and 135 to 709 mm TL for females. Sexual dimorphism between the relationships TL - disc width and TL - total weight was found, with females wider and heavier than males. The mean size at maturity for males was estimated in 530 mm TL and for females in 570 mm TL. The gonadosomatic index (GSI) in mature females varied seasonally and showed the highest value in December. The maximum follicular diameter and oviductal gland width did not show any seasonal pattern. Females with eggs in the uterus were present most of the year. The reproductive activity in males would be continuous throughout the year, evidenced by the lack of variation in the GSI between seasons. The results obtained suggest that A. cyclophora might undergo an annual reproductive cycle, in coincidence to that reported for this species in Brazilian populations.

Highlights

The genus Atlantoraja (Menni, 1972) comprises three endemic species of the Southwestern Atlantic: A. castelnaui, (Ribeiro, 1907), A. cyclophora (Regan, 1903) and A. platana (Günther, 1880)
Females were found to be wider and heavier than males. This dimorphism was found to start at 290 mm TL for both cases, but it was more evident in individuals >500 mm TL
The length frequency distribution significantly differed between sexes and it was more evident between adult individuals

Summary

Introduction

The genus Atlantoraja (Menni, 1972) comprises three endemic species of the Southwestern Atlantic: A. castelnaui, (Ribeiro, 1907), A. cyclophora (Regan, 1903) and A. platana (Günther, 1880) (according to Ebert, Compagno, 2007). Atlantoraja cyclophora is distributed from Cabo Frio, Brazil (22oS) to San Jorge Gulf in Argentina (47oS) and inhabits from the coast out to maximum depths of 300 m in Brazil and up to the 130 m isobath in Argentina (Oddone, Vooren, 2004; Cousseau et al, 2007) This vulnerable species (Massa et al, 2006) is taken as by-catch along all its distribution area by commercial bottom trawl fisheries (Paesch, Domingo, 2003; Oddone, Vooren, 2005; Tamini et al, 2006; Góngora et al, 2009; Estalles et al, 2011; Massa, Hozbor, 2011; Orlando et al, 2011). Like other elsamobranchs (Chiaramonte, Pettovello, 2000; Mabragaña, Cousseau, 2004; Colonello et al, 2007b), a latitudinal gradient in the maximum TL and size at maturity has been noted for A. cyclophora (Oddone, Vooren, 2005; Oddone et al, 2008; Estalles et al, 2011)

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