Blue shark (Bottlenose shark)
Prionace glauca
Tristanians call both Shortfin and Blue shark a Bottlenose shark because they look similar both having blue colouration and a long snout. But Blue sharks are slim and have two long pectoral fins.
Blue sharks are found all over the world where water temperatures are between 12-16 OC, perfect for our Tristan waters all year round.
Their global population is declining mainly because of accidental capture (bycatch) by commercial fisheries offshore and in the high-seas. And sadly they are not released back into the water because their meat and fins are highly valuable in the Asian market.
Their bullet-conical body shape is perfect for their long migratory trips, as they have different areas for prey and reproduction. In 2017 the NatGeo Pristine Seas team recorded mature females and baby blue sharks in our Tristan waters suggesting that we have Blue Shark nursery grounds, now under protection of the MPZ!
Blue sharks create distinctive pairs while mating, with females having a thicker skin layer than males to protect them from males' “love bites”!
Females have a gestation period of 9-12 months producing litters of about 25-35 pups that are around 50cm in size.
In the Atlantic Ocean females start reproducing. When are 5-6 years old, gestation takes around a year and they only live for about 10 years. This means that Blue sharks only produce young twice in their lifetime!
IUCN/ Conservation Status — Near Threatened
Length — Up to 400cm
Weight – more than 200kg
Life span — about 10 years in the Atlantic Ocean
Reproduction — Mainly every other year
Sightings around Tristan islands – All year round but mainly in summer
Marine life on Tristan
The waters surrounding the Tristan islands are home to a diverse range of fish and invertebrates, including the commercially valuable crayfish.