Reproduction and Development 121
dation on their newborn pups. However, not all predators are deterred by
this tactic. For example, some sharks will follow female Spotted Eagle Rays
during the birthing season and snatch up the ray pups shortly after they
are born. As mentioned below, the birth of Broadnose Sevengill Sharks in
San Francisco Bay appears to be timed to take advantage of the later ap-
pearance of young Brown Smoothhounds (Mustelus henleyi), on which the
Sevengill young feed.
Do sharks give birth or lay their egg cases at the same
times and places every year?We now know from tagging and genetic sampling that, in some species
at least, the same females return to the same shallow nursery areas multi-
ple times. Additionally, the time for giving birth is predictable and short in
many species. Nurse Sharks in South Florida have a late November to early
December “pupping” season. Four different elasmobranchs pup in San
Francisco Bay, spreading the pupping season across spring and summer,
although each species has a relatively short season. Female Bat Rays arrive
in late March and give birth two weeks later, in early April. Leopard Sharks
congregate on eelgrass-covered mudflats in small bays and pup in late April
to early May. Broadnose Sevengill Sharks release young between April and
May. Brown Smoothhounds pup a little later, from mid-May to early June.
Such “traditional” birthing and nursery grounds are even suspected
for some of the biggest species, such as Reef Mantas in the Indian Ocean.
These giants aggregate in the Maldive Islands in October and November,
where 80% of the mantas are females and many are very pregnant. Mating
occurs shortly after the females give birth, although no one has yet seen a
manta being born in the wild.
The available evidence on chimaeras also suggests traditional times and
places for egg laying. For example, Australian Elephant Fish lay eggs pre-
dictably during summer and autumn in Port Phillip and Westernport bays,
southern Australia. The eggs then hatch in September and October, the
Australian springtime.
In species with fixed times and places, protection of such pupping areas
is important to conserve the species involved.
How many young does a mother shark produce?
The litter size, or number of young produced, varies among species
from one or two (manta rays; Sand Tiger; Lowfin Gulper Shark, Centro-
phorus lusitanicus) to 300 (Whale Shark, Pacific Sleeper Shark). Most chon-
drichthyans produce intermediate numbers, egg-laying species generally