 Primarily nocturnal , nursehounds spend the day inside small holes in rocks and swim into deeper water at night to hunt . Sometimes two sharks will squeeze into the same hole , and several individuals will seek out refuges within the same local area . In one tracking study , a single immature nursehound was observed to use five different refuges in succession over a period of 168 days , consistently returning to each one over a number of days before moving on . Nursehounds may occupy refuges to hide from predators , avoid harassment by mature conspecifics , and / or to facilitate thermoregulation . In captivity , these sharks are gregarious and tend to rest in groups , though the individuals comprising any particular group changes frequently . This species is less common than the small @-@ spotted catshark . 
