Reproductive biology and abundance of the white-dotted skate, Bathyraja albomaculata, in the Southwest Atlantic

Abstract

Size at maturity, sexual dimorphism, gonad development, and abundance of white-dotted skate, Bathyraja albomaculata, were assessed along its geographic range in the Southwest Atlantic, from Uruguay to Tierra del Fuego (Argentina). In all, 291 specimens from eight research cruises conducted between 1998 and 2003 were examined. Length–mass relationships were sexually dimorphic, adult females being significantly heavier than males of the same length. The largest female observed was 762 mm total length (LT), and 50% maturity (LT50) was attained at 653 mm LT. The largest male was 732 mm LT, and male LT50 was 628 mm LT. Female and male LT50 were not significantly different and were about 86% of observed maximum size, similar to other Bathyraja species. The lack of sexual dimorphism in size at maturity and the slight difference in maximum size between sexes support the hypothesis of relaxation of selection for large female size in oviparous elasmobranchs. Liver size was not sexually dimorphic. Mature female gonads were symmetrical in terms of mass, and similar in ovarian follicle number and size. Females carried egg cases in April, September, and October, consistent with previous observations around the Islas Malvinas and suggesting year-round egg laying. Bathyraja albomaculata was most abundant on the outer continental shelf and slope between 36°30′S and 45°S (northern area). In contrast, it was generally absent between 48°S and 52°S (southern area), a region where it was formerly reported as abundant. These differences are coincident with the development of a fishery targeting skates in the southern area, whereas in the north B. albomaculata taken as bycatch are mostly discarded alive.

Reproductive biology of the skates Sympterygia acuta Garman, 1877 and S. bonapartii Müller & Henle, 1841 (Chondrichthyes: Rajoidei) in south Brazil

“…The number of rows of alar thorns in males of S. bonapartii varied between 1 and 6, in agreement with data reported by Mabragaña et al (2002), and also similar to the pattern observed in A. cyclophora (Oddone & Vooren, 2005) and Bathyraja albomaculata (Ruocco et al, 2006). This sexual character present in males can vary among species, being an important parameter used for maturity staging.…”

“…Other studies have also demonstrated a similarity in this number of maximum of rows of alar thorns, for other species of the same family (Mabragaña et al, 2002;Oddone & Vooren, 2005;Ruocco et al, 2006).…”

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

“…In addition, the higher values in the female GSI observed in December, might be explained by a peak of reproductive activity in spring season, as was proposed by Oddone et al (2008) Mabragaña et al, 2002); A. castelnaui (according to Collonelo et al, 2012); Rioraja agassizi (Müller & Henle, 1841) (according to Colonello et al, 2007a;], where temperatures and photoperiod may affect egg laying rate (Colonello, 2009). The lack of reproductive seasonality is common in deeper waters with less environmental variability, as was observed in B. albomaculata (Norman, 1937) (according to Ruocco et al, 2006), therefore, due to the predominant geographical location of A. cyclophora within the study area (outer coastal shelf, 28.9 -49.6 m bottom depth, 10.6 -14.9ºC mean bottom temperature, Jaureguizar et al, 2006), a mixed coastal-deep reproductive pattern might be possible. On the other hand, the reproductive activity in A. cyclophora males analyzed in this work was continuous through the year, evidenced by the 9 e170098 [9] lack of variation in the GSI between seasons.…”

Age, growth and length-weight relationship of the white skate, Rostroraja alba (Linnaeus, 1758) (Chondrichthyans: Rajidae), from the Gulf of Gabes (Tunisia, Central Mediterranean)

“…But Ebert et al did not reveal significantly difference of this species [16] . The difference between sexes was found for several skates [17,18] . Females reach larger body sizes than males as a consequence of body space needed for egg production and storage during the reproductive stage [18] .…”