Opalescent Inshore Squid
Encyclopedia
The Opalescent Inshore Squid (Doryteuthis opalescens) is a small squid
(mantle
length (ML) up to 190 mm) in the family Loliginidae
. It is a myopsid squid, which is the near shore group and that means that they have cornea
s over their eyes. The species lives in the Eastern Pacific Ocean
from Mexico
's Baja California peninsula
to Alaska
, USA, within 200 miles (320 kilometers) of shore.
length of 13-19 cm, while females are 12-18 cm in mantle length. The mantle of L. opalescens is not fused to the head and its body is 4 to 5 times longer than it is wide, with fins equal in both length and width. This squid has 8 arms with 2 longer tentacle
s ending in tentacular clubs equipped with suckers at their ends. The tentacular clubs are narrow with 4 rows of suckers and 2 large rows in the center of the tentacular club bordered by outer rows of smaller suckers. The 8 arm
s have only 2 rows of alternating suckers running down their length. In male D. opalescens, the left ventral arm is specialized or “hectocotylized
” for spermatophore
transfer during mating. The eyes of L. opalescens are covered with a non-perforated membrane known as a cornea
which is a signature of myopsid
squid. The color of L. opalescens can range from white to brown, with the animals able to change their color shades using chromatophore
s depending on mood and for camouflage. They are normally a bluish-white to mottled brown and gold, and they change to dark red or brown when excited, frightened or feeding.
, and Loligo gahi from the coast of Chile
.
, hatchlings (called paralarva
e), juveniles, and adults. Squid live for 4–9 months. L. opalescens eggs are laid on sandy bottom substrates in 10–50 m depth, although there is a report of a shrimp trawler pulling up eggs from 400 fathom
s (730 m). Females encapsulate hundreds of eggs in a sheath that is made of many layers of protein
. Bacteria
grow between the layers and may serve as an antibiotic
for fungal
infection. Females insert the egg capsules into the sand with a sticky substance that anchors them in place so that the ocean surge can ventilate them. The presence of eggs on the bottom of tanks stimulates females to lay more eggs. Groups of capsules are placed in masses that can extend into egg beds. Some egg beds can cover acres of the ocean floor. The eggs take 3-8 weeks to hatch with warmer water shortening the incubation time. Bat Star
s (Asterina miniatus) are the most prevalent predators of eggs. Fish do not eat them, although they will nip at eggs not covered by the capsule sheath. There is no brooding.
Paralarvae of L. opalescens hatch from the eggs and immediately begin swimming. Where they go is unknown, but hatchlings of the closely related Loligo pealei swim to the surface in the first 12 hours post-hatching. Paralarvae must rapidly learn to hunt, as their yolk is either used up or detached upon escaping from the egg sheath. Through a series of trial and error as these 2–3 mm ML hatchlings learn to eat copepod
s and other plankton
in the first months of their lives. They are found in the greatest abundance at 15 m depth by night and 30 m depth by day. Thus, they perform a daily vertical migration of 15 meters, no small feat a creature only 3 mm long. This daily migration coupled with the shear zone created by tidal and near-shore currents cause the hatchlings to become entrained within 3 kilometers of shore. That is good for them because in the near-shore environment the plankton is smaller and easier for them to eat.
By the time L. opalescens reaches 15 mm mantle length (about 2 months old) they are strong enough to swim in shoals. These juveniles form groups of tens of individuals and swim over the shelf in search of food. Those that have survived to this point can hunt with the tentacular strike as seen in the adults. At some point between 4–8 months their sexual organs mature and they are now considered adults. Sexually mature animals can be 70-160 mm ML and weigh about 40 grams.
Adult L. opalescens move off the continental shelf by day and can be found to depths of 500 m. Adult shoals return to the surface at night to hunt. At some point these shoals move on shore to spawn where aggregations can reach million of individuals. Originally it was thought that the adults died after spawning, as the egg beds were often littered with dead squid. Now there is debate as to how long adults live after their first egg deposition and whether they can spawn repeatedly over the last weeks or months of their lives.
, Blue shark
, Chinook salmon
, Black-throated Diver
, and Brandt's Cormorant
.
The fishery for L. opalescens began with the Chinese
in Monterey Bay, California in 1860. By the turn of the century Italian
fishermen had assumed the leading role. After World War II
there was a resurgence in squid fishing. Since 1981 the fishery has grown significantly, as effort in Southern California has increased. Now Southern California, mostly areas around the Channel Islands
, comprises 90% of the squid landings. The fishery in Monterey Bay
occurs from April to November coinciding with the upwelling season. In Southern California landings begin in November and continue through April correlated with the greater mixing of winter storms. Since 1993 squid has been the #1 fishery in California with landings of 118,000 tons and $41 million in 2000. The population fluctuates greatly with the El Niño. During these warm water and nutrient poor years landings can disappear entirely in certain areas.
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
(mantle
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
length (ML) up to 190 mm) in the family Loliginidae
Loliginidae
Loliginidae, commonly known as pencil squids, is an aquatic family of the order Teuthida .-Species:The following classification follows Vecchione et al. and the Tree of Life Web Project .*Genus Afrololigo...
. It is a myopsid squid, which is the near shore group and that means that they have cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
s over their eyes. The species lives in the Eastern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
from Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
's Baja California peninsula
Baja California Peninsula
The Baja California peninsula , is a peninsula in northwestern Mexico. Its land mass separates the Pacific Ocean from the Gulf of California. The Peninsula extends from Mexicali, Baja California in the north to Cabo San Lucas, Baja California Sur in the south.The total area of the Baja California...
to Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, USA, within 200 miles (320 kilometers) of shore.
Description
Adult Doryteuthis opalescens can reach a total size of 28 cm. Males are typically larger with a mantleMantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
length of 13-19 cm, while females are 12-18 cm in mantle length. The mantle of L. opalescens is not fused to the head and its body is 4 to 5 times longer than it is wide, with fins equal in both length and width. This squid has 8 arms with 2 longer tentacle
Tentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
s ending in tentacular clubs equipped with suckers at their ends. The tentacular clubs are narrow with 4 rows of suckers and 2 large rows in the center of the tentacular club bordered by outer rows of smaller suckers. The 8 arm
Cephalopod arm
A cephalopod arm is distinct from a tentacle, though the terms are often used interchangeably.Generally, cephalopod arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends. Octopuses have eight arms and no tentacles, while squid and cuttlefish...
s have only 2 rows of alternating suckers running down their length. In male D. opalescens, the left ventral arm is specialized or “hectocotylized
Hectocotylus
A hectocotylus is one of the arms of the male of most kinds of cephalopods that is modified in various ways to effect the fertilization of the female's eggs. It is a specialized, extended muscular hydrostat used to store spermatophores, the male gametophore...
” for spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
transfer during mating. The eyes of L. opalescens are covered with a non-perforated membrane known as a cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
which is a signature of myopsid
Myopsina
Myopsina is a suborder of squid containing two families. Some systematists raise it to the level of an order, in which case it is known as Myopsida.-External links:*...
squid. The color of L. opalescens can range from white to brown, with the animals able to change their color shades using chromatophore
Chromatophore
Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development...
s depending on mood and for camouflage. They are normally a bluish-white to mottled brown and gold, and they change to dark red or brown when excited, frightened or feeding.
Misidentification
D. opalescens is very similar to two other species of squid in the same genus: Loligo pealeii from the North Atlantic Coast of North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, and Loligo gahi from the coast of Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
.
Life history
The life cycle of L. opalescens has four stages: eggsEgg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
, hatchlings (called paralarva
Paralarva
Paralarvae is the term used to describe the young planktonic stages of cephalopods, between hatchling and subadult. It is used to differentiate it from the term 'larva' used in animals which undergo true metamorphosis. They have been observed only on members of the orders Octopoda and Teuthida.The...
e), juveniles, and adults. Squid live for 4–9 months. L. opalescens eggs are laid on sandy bottom substrates in 10–50 m depth, although there is a report of a shrimp trawler pulling up eggs from 400 fathom
Fathom
A fathom is a unit of length in the imperial and the U.S. customary systems, used especially for measuring the depth of water.There are 2 yards in an imperial or U.S. fathom...
s (730 m). Females encapsulate hundreds of eggs in a sheath that is made of many layers of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
. Bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
grow between the layers and may serve as an antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
for fungal
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
infection. Females insert the egg capsules into the sand with a sticky substance that anchors them in place so that the ocean surge can ventilate them. The presence of eggs on the bottom of tanks stimulates females to lay more eggs. Groups of capsules are placed in masses that can extend into egg beds. Some egg beds can cover acres of the ocean floor. The eggs take 3-8 weeks to hatch with warmer water shortening the incubation time. Bat Star
Bat star
The Bat star , also known as Sea bat, Webbed star and Broad-disk star, is an echinoderm of class Asteroidea . It typically has five arms or starms, with the center disk of the animal being much wider than the stubby arms are in length. Although the bat star usually has five arms, it sometimes has...
s (Asterina miniatus) are the most prevalent predators of eggs. Fish do not eat them, although they will nip at eggs not covered by the capsule sheath. There is no brooding.
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s and other plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
in the first months of their lives. They are found in the greatest abundance at 15 m depth by night and 30 m depth by day. Thus, they perform a daily vertical migration of 15 meters, no small feat a creature only 3 mm long. This daily migration coupled with the shear zone created by tidal and near-shore currents cause the hatchlings to become entrained within 3 kilometers of shore. That is good for them because in the near-shore environment the plankton is smaller and easier for them to eat.
By the time L. opalescens reaches 15 mm mantle length (about 2 months old) they are strong enough to swim in shoals. These juveniles form groups of tens of individuals and swim over the shelf in search of food. Those that have survived to this point can hunt with the tentacular strike as seen in the adults. At some point between 4–8 months their sexual organs mature and they are now considered adults. Sexually mature animals can be 70-160 mm ML and weigh about 40 grams.
Adult L. opalescens move off the continental shelf by day and can be found to depths of 500 m. Adult shoals return to the surface at night to hunt. At some point these shoals move on shore to spawn where aggregations can reach million of individuals. Originally it was thought that the adults died after spawning, as the egg beds were often littered with dead squid. Now there is debate as to how long adults live after their first egg deposition and whether they can spawn repeatedly over the last weeks or months of their lives.
Predator and prey relationships
L. opalescens is a cannibalistic predator that feeds on smaller prey species such as fish, crabs and shrimp, mollusks, and other juvenile squid. It uses its two longer tentacles with tentacular clubs on the end to snare and catch its prey. L. opalescens itself is an important food source for many predators like larger fish, sharks, marine mammals, sea birds, and also humans. Its predators include the Common Seal, California Sea LionCalifornia Sea Lion
The California sea lion is a coastal sea lion of western North America. Their numbers are abundant , and the population continues to expand about 5% annually. They are quite intelligent and can adapt to man-made environments...
, Blue shark
Blue shark
The blue shark is a species of requiem shark, family Carcharhinidae, that inhabits deep waters in the world's temperate and tropical oceans. Preferring cooler waters, blue sharks migrate long distances, for example from New England to South America. Although generally lethargic, they can move very...
, Chinook salmon
Chinook salmon
The Chinook salmon, Oncorhynchus tshawytscha, is the largest species in the pacific salmon family. Other commonly used names for the species include King salmon, Quinnat salmon, Spring salmon and Tyee salmon...
, Black-throated Diver
Black-throated Diver
The Black-throated Loon is a migratory aquatic bird found in the northern hemisphere. The species is known as an Arctic Loon in North America and the Black-throated Diver in Eurasia, its current name is a compromise proposed by the International Ornithological Committee.-Taxonomy:The...
, and Brandt's Cormorant
Brandt's Cormorant
The Brandt's Cormorant is a strictly marine bird of the cormorant family of seabirds that inhabits the Pacific coast of North America. It ranges, in the summer, from Alaska to the Gulf of California, but the population north of Vancouver Island migrates south during the winter...
.
The fishery for L. opalescens began with the Chinese
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
in Monterey Bay, California in 1860. By the turn of the century Italian
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
fishermen had assumed the leading role. After World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
there was a resurgence in squid fishing. Since 1981 the fishery has grown significantly, as effort in Southern California has increased. Now Southern California, mostly areas around the Channel Islands
Channel Islands of California
The Channel Islands of California are a chain of eight islands located in the Pacific Ocean off the coast of Southern California along the Santa Barbara Channel in the United States of America...
, comprises 90% of the squid landings. The fishery in Monterey Bay
Monterey Bay
Monterey Bay is a bay of the Pacific Ocean, along the central coast of California. The bay is south of San Francisco and San Jose, between the cities of Santa Cruz and Monterey....
occurs from April to November coinciding with the upwelling season. In Southern California landings begin in November and continue through April correlated with the greater mixing of winter storms. Since 1993 squid has been the #1 fishery in California with landings of 118,000 tons and $41 million in 2000. The population fluctuates greatly with the El Niño. During these warm water and nutrient poor years landings can disappear entirely in certain areas.