Male-biased sexual size dimorphism in sharks: the narrowmouth catshark Schroederichthys bivius as case study

Abstract

In shark populations, variation in sexual size dimorphism (SSD) appears to be related with the reproductive mode. Here, we aimed to investigate the reproductive biology of the narrowmouth catshark Schroederichthys bivius, an oviparous shark with size and secondary sexual dimorphism. For this purpose, specimens were collected during research surveys covering almost their entire distribution in the southwestern Atlantic continental shelf. Size distribution ranged from 196 to 810 mm total length (TL) in males and from 258 to 630 mm TL in females, and the mean size at maturity was 563 mm TL for males and 485 mm TL for females. Males appeared to be capable of mating all times of the year, while females could exhibit an annual reproductive cycle. Besides SSD, with males attaining higher maximum TL and size at maturity, spatial sexual segregation appears to be observed in mature specimens. Although differences in size at maturity were observed between surveys, these differences did not show a latitudinal pattern. The spatial overlap observed between closed areas to trawling and the distribution of egg-bearing females suggests that these closed areas, although designed and established to protect other species, may represent an important measure also for the conservation of S. bivius.