Reproduction and Development 129
southern end of the Gulf of California near La Paz and in the Galapa-
gos Islands. The known feeding aggregations at Ningaloo Reef off western
Australia, in the Maldives, at Gladden Spit off Belize, and off Djibouti near
the Arabian Peninsula contain mostly males, most of which are juveniles.
Some chimaeras also form sex-specific, or at least sex-dominant, groups.
Of 62 individual Rabbitfish caught in a small area of the North Atlantic,
82% were females, mostly of adult size. The Spotted Ratfish also segre-
gates by sex; males and females occur in separate groups, with juveniles of
both sexes aggregating in deeper water than adults. Australian Elephant
Fish show the opposite pattern, younger fish occurring in shallower areas
than adults. Sex segregation in chimaeras may be a general trend, but we
know details only about the species that occur in shallower areas accessible
to sampling and fishing gear.
The occupation of shallower water by younger fish, regardless of sex, is
a distribution pattern more typical of fishes in general. This pattern prob-
ably applies to many shark species, especially the ones that use nearshore
pupping and nursery areas (see “Where do sharks lay their eggs or give
birth?” above).
At what size and age do sharks mature?
Male and female elasmobranchs can be told apart almost at birth be-
cause of a male’s claspers (and a female’s lack thereof). However, the clasp-
ers of an immature male are not very impressive, which is to say they are
pretty small. When the male matures, there is sudden and obvious clasper
growth, something we can tell just by looking at the outside of the animal.
The claspers also become calcified (hardened). For females, it’s more dif-
ficult to pinpoint the size at maturity. Accurate determination usually re-
quires dissecting the reproductive tract and finding developing eggs. But
we have a good idea for many species. In some species, males and females
mature at about the same ages and sizes; in many others, one sex matures
smaller and/or younger than the other.
Sizes at maturation vary greatly among sexes and locales. In general,
females mature at larger sizes and greater ages than males. For example,
Scalloped Hammerhead males mature at 140 to 165 cm (5.5 ft), females at
210 cm (7 ft). Basking Shark males mature at 450 to 600 cm (15–20 ft), with
females maturing between 700 and 1,000 cm (23–33 ft). Shortfin Mako
Shark males mature at 200 to 215 cm (6.5–7 ft), while mature females are
much larger, at 275 to 290 cm (9–10 ft). Batoids and holocephalans show
similar patterns.
Ages at maturity vary in species depending on sex and also as a function
of where the sharks occur. In species in which the sexes mature at differ-