Reproduction and Development 131
Striking differences also occur in species that have wide geographic
ranges. Salmon Sharks in the northwestern Pacific mature at 5 years (males)
and 8 to 10 years (females), whereas males of the same species in the north-
eastern Pacific mature as young as 3 years old and females at 6 years old.
Spiny Dogfish (Squalus acanthias and S. suckleyi) occur around the world at
temperate latitudes. The average age at maturity for S. acanthias females
is reported as 7 to 8 years off eastern Canada, 9 to 11 years off the British
Isles, and 12 years along the U.S. Atlantic seaboard. S. suckleyi matures at
even greater ages: 20 years in the northwestern Pacific and 35 years along
the British Columbia coast.
The take-home message from these comparisons is that sharks and
their relatives are slow to reach maturity. On average, female sharks don’t
mature until they are 17 years old, and batoids don’t mature until they are
about 8 years old.
How long do sharks live?
Compared with bony fishes or small mammals or birds, sharks and their
relatives tend to live a long time. The average longevity for larger sharks is
35 years, and for batoids 26 years. Chimaeras don’t appear to live as long as
sharks or rays, but again we have age information on only a few species, and
these species may not be representative of the group as a whole.
Looking at particular species that many people are interested in is a
little frustrating. For example, we are not sure how long White Sharks live,
but we do know they can live as long as 22 years and maybe as long as
30 years. That first number comes from growth rings on the vertebrae of
dead sharks. Supporting information comes from photographs of the dor-
sal fins of five White Sharks off central California. These animals were
seen over a 16- to 22-year time span. Sharks have the same marks and scars
for that long, which allows researchers to identify individuals. Dorsal fin
marks were also used to establish that Nicole—the female tagged off South
Africa, tracked to western Australia, and then rediscovered back off South
Africa—was the same animal (see “Do sharks migrate?” in chapter 5). Such
data also demonstrate that the same sharks return to the same locales year
after year. Longevity information for Reef Mantas is similarly limited to
sightings of known individuals. One female was seen repeatedly in the
Maldives for 22 years and was mature when first observed, making her at
least 32 years old. Information on observed maximum ages for a variety of
Chondrichthyes is presented on page 130.
We don’t know how long Basking Sharks live because we don’t have a
reliable way of measuring their ages (see the end of the next question).