The unusual teeth of the dusky smoothhound are adapted to crushing and grinding prey, rather than biting and tearing it like most other shark species (1) (3) (6). It is an active, nocturnal predator (2) (3) (7) which feeds mainly on large crustaceans, such as rock crabs (Cancer irroratus), lady crabs (Ovalipes ocellatus), blue crabs (Callinectes sapidus) and lobsters. The dusky smoothhound also eats squid, small fish, worms, razor clams (Ensis directus) and other molluscs, and occasionally garbage, such as discarded chicken heads (2) (3) (4) (8). Juveniles feed mainly on crabs, small shrimps and worms (3) (9).
In the North Atlantic Ocean, the dusky smoothhound mates from mid to late summer. The young are born the following May to July (2) (3) (9) (10), after a gestation period of 10 to 12 months (2) (3) (5) (10). In other parts of its range, births may be less seasonal (11). The dusky smoothhound is viviparous, giving birth to live young which have been nourished inside the female by a yolk-sac placenta (2) (3) (4) (5). The female may give birth to between 3 and 20 young at a time, with larger females having larger litters. The young measure about 28 to 39 centimetres at birth (2) (3) (4) (5) (9) (10).
The dusky smoothhound has been recorded using shallow estuaries and tidal marshes as nursery grounds, where the females give birth and where the young then remain and develop for several months (9). This species grows relatively quickly for a shark, with males reaching maturity from about 82 to 99 centimetres in length, and females from about 90 to 108 centimetres (2) (4) (5) (11) (12). These lengths correspond to ages of two to three years and four to five years, respectively (3) (10). The female dusky smoothhound may grow larger than the male (11), and maximum body size is reached at around seven to eight years of age (3). Females may live for up to 16 years in the wild, and males for around 10 years (3) (12).