Brooding Squid Discovered
The mothering instinct is inherent in many animals, but completely absent in others. For instance, humans care for their children for 18 (or more!) years, while the giant tortoise lays her eggs on a moonlit beach and then abandons her progeny to make their own way in their watery world. Scientists have always considered the squid to be a follower of the latter style of parenting; however, deep-sea explorers were recently surprised to discover a female squid caring for a large sac of eggs.
This protective behavior was demonstrated by the female Gonatus onyx squid, a common species found in surface waters, and was caught on tape by marine biologist Brad Seibel of the University of Rhode Island and his colleagues. The video evidence of the squid puts to rest a long controversy, said squid expert Eric Hochberg of the Santa Barbara Museum of Natural History in California. Hochberg was part of a team of researchers that proposed the existence of brooding squid five years ago based on the retrieval of a trawl bucket in 1996 that contained a relatively small number of extraordinarily large eggs along with an adult Gonatus onyx squid. "We just always had assumed that octopuses carry eggs and squids lay them on the bottom," said Hochberg. But the discovery of the Gonatus onyx changes these previous assumptions and, according to Hochberg, "there may be other deep-sea squids that are carrying their eggs."
These particular squids care for their precious cargo between 5,000 and 7,000 feet below the surface off California's central coast, just above the inky abyss of the Monterey Canyon. Because surface waters and the ocean floor are considered the two most productive depths for marine life, this middle-depth location may explain why the squid's parenting behavior was not observed until now. According to Siebel, "Researchers tend to skip this zone." The squids are probably brooding in this area to hide from predatory whales and seals, which also tend to ignore the middle depths while hunting.
Most squids lay 10,000 to 100,000 small eggs and leave them on the ocean floor where only a few survive to adulthood. But by watching over their eggs for six to nine months until they hatch, the newly discovered brooding squid enhances the survival odds of each egg, thereby allowing them to lay fewer and larger eggs.
The female Gonatus onyx carries approximately two to three thousand eggs in an open-ended sac she holds with hooks in her arms and keeps oxygen flowing to the eggs by circulating water through the sac. But after the eggs are ready to hatch, the mother probably dies, said Seibel. "Most squids lay eggs and die in one season," said Seibel. Because the egg sac blocks the squid's mouth, it's very difficult to eat with it and there's no evidence she can release it to feed and then pick it up again. Scientists have compared squids that are carrying freshly laid eggs to those holding older eggs that are ready to hatch. The squids with mature eggs are physically wasted and ready to die, whereas those with younger eggs look much healthier. The female squids accumulate fat stores while they grow and then expend it during the brooding period, which may last up to nine months. Scientists theorize that the squids' metabolism slows considerably during brooding to conserve energy and that prolonged muscle degeneration gradually provides increased buoyancy to support the eggs. They also believe the high lipid content of the females' digestive gland provides the fuel necessary to survive the brooding period.
This discovery is a prime example of how an important food source for shallow-water species and birds can also require deep waters for its survival. For this reason, Siebel says, it's important for people to think twice before signing on to any disposal project or other plans that can pollute deep ocean waters.
Click here to watch a video of a squid carrying a tubular pouch of thousands of eggs.