Cat-like eyes help these sharks see in the dark.

Deep-sea catsharks (family Pentanchidae) prowl the waters just above the deep seafloor, searching for small fishes and invertebrates. Keen senses help them find prey in these dim depths. 

Much like the eyes of house cats, the eyes of deep-sea catsharks have a mirrored lens to see better in the dark. Called the tapetum lucidum, this layer of tiny crystals behind the retina reflects light back into the eye to improve vision under low-light conditions. Like other sharks, deep-sea catsharks also have a sixth sense. Tiny gel-filled pits—known as the ampullae of Lorenzini—under their snouts can sense the electrical impulses of prey, revealing a meal buried in the mud.

Scientists have described more than 100 different species of deep-sea catshark from waters around the world. In fact, deep-sea catsharks represent the largest family of sharks alive today. Most are small, typically only 80 centimeters (31 inches) long. They often have a long, slender shape with dorsal fins set further back on their bodies. We have encountered four different catshark species off the west coast of the United States and the waters around Baja California.

While many sharks give birth to live young, most catsharks lay egg cases. But catshark mothers do not incubate their eggs—they deposit two egg cases at a time and leave them to develop on their own. Tough keratin—the same material as human fingernails—protects the developing embryo inside. 

Twisted tendrils anchor the egg case to sponges or corals, but sometimes a mother catshark attaches her egg cases to other egg cases. We have observed large “chandeliers” of leathery egg cases hanging from the rocky ledges of canyon walls. By leaving her egg cases dangling in the currents, a mother catshark reduces the risk that her developing young will become fouled by bacteria.

Sharks help support a healthy ocean, but their populations worldwide are in decline. Overfishing, fisheries bycatch, and habitat destruction threaten these magnificent animals. Deep-sea sharks are particularly at risk because they grow slowly and reproduce late in life. Our work to understand deep-sea catsharks and their kin is providing information that resource managers can use to protect these amazing animals of the deep and the habitats they call home.