Dark Shyshark - Biology and Ecology

Biology and Ecology

The dark shyshark is a generalist predator whose main food sources are, in descending order of importance, small benthic crustaceans, bony fishes, and molluscs. Larger sharks consume proportionately more crustaceans. Polychaete worms and echinoderms are also taken on occasion, and algae may be swallowed incidentally. This species is preyed upon by the broadnose sevengill shark (Notorynchus cepedianus), and potentially also other large fishes and marine mammals. When threatened, it adopts a characteristic defense posture in which it curls into a ring with its tail over its eyes; this behavior likely makes the shark harder to swallow and is the origin of the common names "shyshark" and "doughnut". In captivity, the whelks Burnupena papyracea and B. lagenaria have been documented piercing the egg cases of this species and extracting the yolk. A known parasite of the dark shyshark is the trypanosome Trypanosoma haploblephari, which infests the blood.

Like other members of its genus, the dark shyshark is oviparous; adult females have a single functional ovary and two functional oviducts. There appears to be no distinct breeding season and reproduction occurs year-round. Females produce mature eggs two at a time, one per oviduct. The eggs are enclosed in purse-shaped capsules measuring 5.5 cm (2.2 in) long and 2.5 cm (0.98 in) across; each capsule is plain amber to dark brown in color and bears thin, coiled tendrils at the four corners. In one observation of an egg that hatched after 104 days, the developing embryo had external gill filaments until it was 50 days old, and completely absorbed its yolk sac shortly before hatching. Eggs in nature typically hatch in 6–10 months, with the newly hatched shark measuring 10–12 cm (3.9–4.7 in) long. Both sexes grow at approximately the same rate, reaching sexual maturity at around 15 years of age. Mature males and females range from 40–57 cm (16–22 in) and 36–60 cm (14–24 in) long respectively. The maximum lifespan is 25 years.