Sperm whales are very very massive animals, but in relation to their size, they have very thin skin, and this skin isn´t very hard too, as the many scars of squid suckers and teeth on the bodies of bulls show. But sharks have very thick and hard skin, all, including sleeper sharks, and all have small teeth on the surface of the skin, which makes them not only faster, but also better protected against attacks. I have still the remains of a sharks skin from a shark-steak I ate. The steak belonged to an animal which was surely not longer than 2m, but the skin was about 5mm thick (it was probably a female, because they have thicker skin) and very hard, I had even problem to cut it with a sharp knife. In this case I don´t wonder why sharks show no sucker markings on their skin. Sleeper sharks can grow very large, about as large or perhaps even larger than great whites, although their size is often exagerated in the popular press. A specimen of 5m would have an armour-like skin of nearly 2cm thickness.
Sleeper sharks are often said to be inactive scavengers, but in fact this animals also hunt actively. It would also be strange if such large animals could always find enough carrion. They hunt no only fish and squid, but also often seals, and greenland sharks were even found with whole rendeers in their stomaches, they probably killed when a herd did swim in a fjord or between isles.
Sleeper sharks are often said to be inactive scavengers, but in fact this animals also hunt actively. It would also be strange if such large animals could always find enough carrion. They hunt no only fish and squid, but also often seals, and greenland sharks were even found with whole rendeers in their stomaches, they probably killed when a herd did swim in a fjord or between isles.