Cephalopods have figured in the art and literature of many human cultures. Stories of large or intelligent cephalopods are well known from many ocean-oriented cultures, including Japanese, Polynesian, and Western European. Octopods are depicted on classical Greco-Roman pottery, frescoes, and similar artifacts. Medieval Germanic legends about "Kraken" or sea monsters probably refer to giant squids. Even at the present time, large squids and octopods continue to be subjects of much public interest. For example, the giant squid was described in a special issue of Time magazine on ocean exploration as "the last bona fide sea monster." This interest has been sustained by a series of popular novels and movies.
Many species of squid, cuttlefish, and octopod are very good food when prepared properly. Many people around the world enjoy dishes made from certain species of cephalopods. Fishermen also often equate cephalopods with "good bait" because other marine species like to eat them as well. These culinary considerations, both human and otherwise, reflect the importance of cephalopods in commercial fisheries and marine food webs. Although worldwide fisheries for squids, cuttlefishes, and octopods are dwarfed in comparison with those for shrimps, bivalves, and many fishes, catching and marketing cephalopods can dominate such local economies as that of the Falkland Islands. The total cephalopod catch officially reported for the year 2000 was about 4.0 million tons (3.6 million metric tons); this figure represents about 4.2% of the world total marine catch for the same year. Some statistics indicate that as humans reduce the populations of competing and predatory fishes and mammals, regional populations of cephalopods are increasing.
Octopods occasionally are considered to be pests in trap fisheries for mollusks (e.g., whelk) and crustaceans (e.g., lobsters) because the octopods enter the traps and eat the catch.
The rediscovery of squid giant axons by J. Z. Young in the 1930s allowed experiments that demonstrated much of what is known about the basic functioning of nerves. The giant axons of squid nerves have been widely used as one of the primary bases of neurobiology. Cephalopods are also being used increasingly as models in other biomedical fields, including sensory biology, information processing, and biochemistry. They are even being used as a source of information regarding the detoxification of nerve gas. The results of an electronic search of scientific literature for the word "squid" may be dominated by biomedical studies based on inshore squid as a convenient and interesting model.
Cephalopod bites, especially by octopods, can be painful at the least. Some are poisonous because of the injection of salivary secretions, and may even be lethal on rare occasions. Poisonous bites from the small blue-ringed octopus, Hapalochlaena spp., which secretes a substance known as cephalotoxin, have resulted in documented human deaths. Furthermore, schools of the large Humboldt squid, Dosidicus gigas, are reported to attack scuba divers and fishermen who have fallen into the water.
Many marine animals of particular interest to people, like whales, specialize in eating cephalopods. Among the ani mals with large brains that people consider intelligent, the cephalopods are unique because they are not vertebrates. The cephalopod brains and their remarkably familiar eyes have developed from an early precursor completely unlike the forerunners of dogs, dolphins, parrots, lizards, and fishes. This evolutionary history makes cephalopods the closest thing to an alien intelligence that humans have ever encountered.
Because cephalopods are important to biomedical researchers and fisheries, cephalopod biology is comparatively well-known from a few inshore species that can be caught close to such major marine biological laboratories as those in the northeastern United States; Plymouth, England; Naples, Italy; and Hakodate, Japan.
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