After two months, the embryo measures long and has well-developed external gills. After four months, the yolk sac has begun to be converted into a placental connection that attaches to the uterine wall; at this time, the embryo's dark fin markings develop. By five months, the embryo measures and has resorbed its external gills; the placenta is fully formed, though some yolk remains until seven months into gestation. Parturition occurs from September to November, with females making use of shallow nursery areas interior of the reef. Newborn pups measure long in the Indian Ocean and off northern Australia, while free-swimming pups as small as long have been observed in the Pacific islands. The litter size is 2–5 (typically 4), and is not correlated with female size. Young blacktip reef sharks commonly form large groups in water barely deep enough to cover their bodies, over sand flats or in mangrove swamps close to shore. During high tide, they also move onto flooded coral platforms or seaweed beds. Growth is initially rapid; one documented captive shark grew an average of per year in its first two years of life. The growth rate slows to around per year in juveniles and adults. Males and females mature sexually at lengths of and respectively off northern Australia, and and , respectively, off Aldabra. Males mature at long off Palmyra Atoll. Under most circumstances, the blacktip reef shark has a timid demeanor and is easily frightened away by swimmers. However, its inshore habitat preferences bring it into frequent contact with humans, and thus it is regarded as potentially dangerous. As of early 2009, 11 unprovoked attacks and 21 attacks total (none fatal) were listed on the International Shark Attack File that are attributable to the blacktip reef shark. Most attacks involve sharks biting the legs or feet of waders, apparently mistaking them for their natural prey, and do not result in serious injury. In the Marshall Islands, native islanders avoid blacktip reef shark attacks by swimming rather than wading through shallow water, and a way of discouraging these sharks is to submerge one's body. The blacktip reef shark has also been known to become aggressive in the presence of bait, and may pose a threat while attempting to steal the catches of spear fishers. The blacktip reef shark is a normal catch of coastal fisheries, such as those operating off Thailand and India, but is not targeted or considered commercially important. The meat (sold fresh, frozen, dried and salted, or smoked for human consumption), liver oil, and fins are used.