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.

中文翻译：

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鲨鱼的雄性性别大小二态性：窄口猫鲨 Schroederichthys bivius 作为案例研究

在鲨鱼种群中，性别大小二态性 (SSD) 的变化似乎与繁殖方式有关。在这里，我们旨在研究窄口猫鲨 Schroederichthys bivius 的生殖生物学，这是一种具有大小和第二性二态性的卵生鲨鱼。为此，在研究调查期间收集了标本，几乎涵盖了它们在西南大西洋大陆架的整个分布。雄性总长度 (TL) 的大小分布范围为 196 至 810 毫米，雌性为 258 至 630 毫米，成熟时的平均长度为雄性 563 毫米 TL 和雌性 485 毫米 TL。雄性似乎能够在一年中的所有时间交配，而雌性则可以表现出一年一度的生殖周期。除了 SSD，雄性在成熟时获得更高的最大 TL 和大小，在成熟标本中似乎观察到空间性分离。尽管在调查之间观察到成熟时的大小差异，但这些差异并未显示出纬度模式。在拖网捕捞的封闭区域和产卵雌性分布之间观察到的空间重叠表明，这些封闭区域虽然是为保护其他物种而设计和建立的，但也可能代表了保护 S. bivius 的重要措施。