Crested Bullhead Shark - Biology and Ecology

Biology and Ecology

The crested bullhead shark is a slow-moving, nocturnal species often seen wedging its head between rocks in search of food. It feeds primarily on the sea urchins Centrostephanus rodgersii and Heliocardis erythrogramma, but has also been known to take a variety of other invertebrates and small fishes. A steady diet of sea urchins may stain the teeth of this shark pinkish purple. The crested bullhead shark is also a major predator of the eggs of the Port Jackson shark, which are seasonally available and rich in nutrients. Individual sharks have been observed taking the egg capsules in their mouths and chewing on the tough casing, rupturing it and allowing the contents to be sucked out; egg capsules may also be swallowed whole. Unlike the Port Jackson shark, the crested bullhead shark is not known to form large aggregations.

Crested bullhead sharks are oviparous with a possibly annual reproductive cycle. Females produce 10–16 eggs per year during late winter in July and August, though Michael (1993) noted that egg laying may continue year-round. The egg cases measure around 11 cm (4.3 in) in length, with a pair of thin flanges spiraling 6–7 times around the outside and two slender tendrils up to 2 m (6.6 ft) long at one end, used to attach the capsule to seaweed or sponges. The capsules are usually deposited at a depth of 20–30 m (66–98 ft), much deeper than the Port Jackson shark, though there is a single record of an egg being found only 8.6 m (28 ft) down. The time to hatching has been variously reported as 5 and 8–9 months; the newly emerged young measure 17–22 cm (6.7–8.7 in) long and resemble the adults. Last and Stevens (1994) gave the lengths at maturity for males and females at 60 cm (24 in) and 70 cm (28 in) respectively, though mature males as small as 53.5 cm (21.1 in) long were later found off Queensland. Growth and aging has been documented for one captive female at the Taronga Park Aquarium, which grew an average of 5 cm (2.0 in) per year and did not lay eggs until she was almost 12 years old.