fecundity egg protectors and free-spawners with high fecundity extends well down in
the water column.
(^) Sexes are separate in the squids and octopods, including those of the deep sea.
Mating involves the male attaching a packet of sperm, a spermatophore, inside the lip
of the female’s mantle. The female then dispenses the sperm from a seminal
receptacle organ to fertilize her eggs. Females develop very large ovaries at the
expense of body tissue, and after mating they spawn and die. Hatchlings of a few
millimeters have a body form like that of adults, but with relatively shorter arms. The
larvae usually live in near-surface layers, working down as they grow. Squid growth is
often extremely rapid, especially in forms that migrate up to the surface at night,
leading to life cycles of only a year or two. Many of the more active, vertically
migratory species also undertake mating and spawning migrations along continental
coasts. For example, Todarodes pacificus spawns in the northeast corner of the East
China Sea adjacent to Kyushu and the Tsuchima Strait (Okutani 1983). An adult
female of about 50 cm total length (26 cm mantle length) produces masses of eggs in
a gelatinous matrix the size of a soccer ball. These blobs are released near the
seafloor, and they are dense enough that they do not rise. Females of this size have
been estimated to produce up to 470,000 eggs 0.8 mm in diameter in several such
blobs. “Nidamental” glands associated with the oviducts produce the gelling agent; it
is now extracted by squid fisheries as a by-product and used for thickening ice cream.
Hatching larvae are carried north through the Sea of Japan, and along the east coast of
Japan inside the Kuroshio, to feeding grounds in the vicinity of Tsugaru Strait
between Hokkaido and Honshu. There they feed and grow until the adults nearing
mating condition swim back to the spawning grounds. The feeding grounds are the
site of a large night-time fishery that uses brilliant lanterns, as visible from space as a
large city, to attract the squid to barbed jigs. A similar migratory and reproductive
pattern is followed by Illex illecebrosus along the US East Coast (O’Dor 1983),
spawning over the outer shelf and slope south of Cape Hatteras, then moving north
with the Gulf Stream to feed near Newfoundland. Its egg masses also sink. Some non-
migratory, mesopelagic species have highly modified larvae; for example, the
doratopsis larva of the Chiroteuthidae has odd swimming mechanics and a
pronounced metamorphosis to the adult form. Much remains to be learned about
reproduction in the fully oceanic and deep-living squid that do not migrate into
surface waters at night.
(^) Mesopelagic fish, according to Marshall (1979), are quite uniform in their
reproductive patterns; most (all?) produce eggs less dense than their surroundings. He
says they do that by excluding salts from the oocytes before spawning, presumably
replacing their osmotic effect with ammonium (or something light). Salts are excluded
by an outer membrane (chorion) impermeable to them. Data demonstrating this
proposed mechanism are hard to find. Most mesopelagic fish eggs also have a small