Position of Recapture
Map of Blue Shark's Migratory Route
We tagged a Blue Shark on the 02.08.2010, 6 miles south of St Mary's. It has been recaptured on the 07.02.2012, 250 miles West of Sierra Leone and 200 miles North of the Equator 3,300 miles from were we tagged it.
Blue sharks are highly migratory and travel further distances than any other shark, migrations of 1,300 to 1,800 miles are common and journeys of 3,700 miles have been recorded in the Atlantic Ocean. In the Pacific Ocean, Blue Sharks have been found to travel even longer distances of up to 5,700 miles. The Blue Sharks’ complex migratory patterns are believed to be linked to reproduction, populations of mature males and females meet to mate and pregnant females migrate huge distances to give birth well away from other mature sharks and the distribution of their prey. Different sexes and ages undergo different patterns of movement, young male and female sharks are usually found in different areas, and mature adults are also separated for most of the year.
Genetic analysis indicates that the Blue Sharks of the western and eastern North Atlantic represent a single breeding stock. Mating takes place in the western North Atlantic during spring and early summer (May through to July). Incredibly many of the recently-mated female Blue Sharks in the western North Atlantic are not yet sexually mature; they store the sperm packets in special sacs (shell glands) within their reproductive tract. As they migrate on their transatlantic journey eastward across the North Atlantic the adolescent female Blues mature and begin passing ripe ova through their shell glands where the sperm packets are stored and fertilization takes place. Roughly a year after a female Blue Shark was inseminated in the western North Atlantic, she self-fertilizes during her epic eastward migration. Most of the male blue sharks will remain in the western North Atlantic. The gestation period is 9-12 months, resulting in a large litter of between 4-135 pups at a length of 35-50 cm born in the spring or summer months. The number of pups varies among females and is thought to be related to the size of the female. Pups are live born (known as vivipary) in nursery areas. They will remain here until they reach a length of about 130 cm at which time they will begin to migrate. By the age of maturity, their migration patterns will resemble those of other Blue Sharks.