Grey Nurse sharks - reproduction
Grey nurse sharks produce only 2 pups at a time. Unusually for sharks they are born headfirst. Shark pups are born able to fend for themselves and the adults show little parental care. Studies on North Atlantic populations have shown that grey nurse sharks initially grow at about 30 cms per year, steadily declining to about 10 cms a year. Males mature at about 1.9m (4-5 years) and females at about 2m (6 years). They grow to a maximum size of 3.2m and an age of about 15 years. Male sharks can be recognised by a pair of claspers (penis like structures) on their undersides behind their pelvic fins. Female sharks have two uteri which share a common opening. In most shark species the males hang on to the females by biting during intercourse. Female sharks often have thicker skins than males. Generally only one clasper at a time is used in intercourse. Male grey nurse sharks in captivity have been seen to show dominance displays. Bites on the tails of young males or around the gills of females and discarded teeth in aggregation areas may be evidence of mating activity.
After internal fertilisation, embryos develop in each of the two uteri. They are enclosed in egg cases and have no placental connection to the mother. When the young have consumed their yolk supplies they hatch inside the uteri. The largest embryo in each uterus will eat its brothers and sisters. The mother will continue to produce unfertilised egg on which the young also feed. After 9-12 months 1 pup will emerge from each uterus with a litter every 2 years.