Avoiding being dragged away: finding egg cases of Schroederichthys bivius (Chondrichthyes: Scyliorhinidae) associated with benthic invertebrates.

Egg cases of the narrowmouthed catshark Schroederichthys bivius were recorded entangled with sponges, corals and tubeworms at different sites in the south-west Atlantic Ocean. This work sheds light on the importance of benthic invertebrates in the life cycle of oviparous chondrichthyan species.

Reproductive and population parameters of spiny dogfish Squalus acanthias in the south-western Atlantic Ocean.

The objective of this study was to estimate reproductive and population parameters of the spiny dogfish Squalus acanthias for the south-western Atlantic Ocean. In total, 2714 specimens (1616 males and 1098 females) were collected from surveys carried out using research vessels. Males ranged from 225 to 861 mm total length (LT ) and females from 235 to 925 mm LT . The size at maturity of females (651 mm) was significantly greater than that of males (565 mm). The maximum proportion of mature individuals (Pmax ) of the gestation ogive was <1, which indicates that a proportion of mature females was not in gestation. This inactivity may be explained by the occurrence of resting periods between cycles or by the asynchrony of the reproductive cycle. The estimated Pmax for the maternity ogive suggested that about one third of mature females were in the maternity stage (i.e. with embryos >156 mm). The temporal and spatial co-occurrence of non-gravid adult females at different stages of ovarian development, as well as gravid females at all embryonic development stages would indicate that the female reproductive cycle in the south-western Atlantic Ocean is asynchronous. The results indicate that S. acanthias is susceptible to fishing pressure on account of its length at maturity, extended reproductive cycles and low fecundity.

Trophic ecology of yellownose skate Zearaja chilensis, a top predator in the south-western Atlantic Ocean.

The diet and trophic level (TL ) of the yellownose skate Zearaja chilensis in the south-western Atlantic Ocean (35°-54° S), and how these varied in relation to body size, sex, maturity stage, depth and region were determined by analysis of stomach contents. From 776 specimens analysed, 671 (86·5%) ranging from 180 to 1190 mm total length (LT ) had prey in their stomachs. The diet was dominated by fishes, mainly the notothenioid Patagonotothen ramsayi and the Argentine hake Merluccius hubbsi. The consumption of fishes and crabs increased with increasing predator size, and these preys were more important in the north than in the south. Isopods and other crustaceans were consumed more in the south and their consumption decreased as the size of Z. chilensis increased. The TL of Z. chilensis increased with LT from 4·29 to 4·59 (mean 4·53), confirming their ecological role as a top predator. The small and large size classes exhibited a low diet overlap and the highest spatial segregation, whereas medium and large specimens had higher co-occurrence and dietary overlap indices. A clear distinction in tooth shape was noted between sexes in adult specimens, with males having longer cusps. This sexual heterodonty may be related to reproductive behaviour, increasing the grasping ability of males during courtship, because there were no differences in diet between the sexes.