The Humboldt squid (Dosidicus gigas), also known as jumbo squid or jumbo flying squid, is a large, predatory squid living in the eastern Pacific Ocean. They are the most important squid worldwide for commercial fisheries, with the catch predominantly landed in Chile, Peru and Mexico. Because Humboldt squid (and oceanic organisms in general) spend most of their time far beneath the ocean surface, there are limited opportunities to observe their behavior. The study of these relationships between organisms and their interactions with the environment is called ecology. Trophic ecology is specifically the study of interactions between predators and prey.
Physical Characteristics and Distribution
Humboldt squid typically reach a mantle length of 1.5 m (5 ft), making the species the largest member of its family. Some individuals may grow to 1.5 m (5 ft) in mantle length and weigh up to 50 kg (110 lb). They appear to be sexually dimorphic: on average the females mature at larger sizes than the males. Generally, the mantle (or body) constitutes about 56-62% of the animal's mass (which includes the fins or wings), the arms and tentacles about 11-15%, the head (including eyes and beak) about 10-13%, the outer skin (cuticle) 2.5-5.0%, the liver 4.2-5.6%, with the rest made up of the other inner organs. The gonads consist of 1.5-15.0% of the total mass. The gladius (the single inner 'bone') is 0.7-1.0%. They are propelled by water ejected through a hyponome (siphon) and by two triangular fins. These squid can weigh up to 50kg and have a mantle length of up to 2m.
The Humboldt squid lives at depths of 200 to 700 m (660 to 2,300 ft) in the eastern Pacific (Notably in Chile and Peru), ranging from Tierra del Fuego north to California. Ventral view of D. Humboldt squid are generally found in the warm Pacific waters off the Mexican coast. In recent decades, the Humboldt squid has undertaken a massive expansion in geographic range. Historically, it was common from Peru to central Mexico, but now they stretch from the tip of Chile to Alaska. There is a very large population in the Gulf of California, Mexico that scientists believe only recently became established there, and this species is now common throughout California.
Humboldt Squid Behavior
Like other members of the subfamily Ommastrephinae, they possess chromatophores which enable them to quickly change body coloration, known as 'metachrosis' which is the rapid flash of their skin from red to white. The entire body flashes between the colors red and white at 2-4 Hz when in the presence of other squid, this behavior likely representing intraspecific signaling. This flashing can be modulated in frequency, amplitude and in phase synchronization with each other. The other chromogenic mode is a much slower "flickering" of red and white waves which travel up and down the body, this is thought to be a dynamic type of camouflage which mimics the undulating pattern of sunlight filtering through the water, like sunlight on the bottom of a swimming pool.
Humboldt squid are carnivorous marine invertebrates that move in shoals of up to 1,200 individuals. They swim at speeds up to 24 km/h (15 mph; 13 kn). Electronic tagging has shown Humboldt squid undergo diel vertical migrations, which bring them closer to the surface from dusk to dawn. Humboldt squid are thought to have a lifespan of about a year, although larger individuals may survive up to 2 years.
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Diet and Feeding Habits
Humboldt squid play a major ecological role in their open ocean environment. They are eaten by many marine animals, but are also voracious generalist predators, feeding on almost anything they can catch. Humboldt squid grow rapidly, some reaching 6ft long and over 100lbs in less than two years. This amazing growth rate is fueled by their success as predators. Young hatchlings have an internal yolk sac that supports them for a few days, but they must quickly learn to hunt on their own. We are currently unsure what these tiny squid eat, but we suspect they eat plankton—small drifting plants and animals. As Humboldt squid grow larger and become more skilled at hunting, they devour larger fishes, crustaceans, and other species of squid. Relative to their body size, Humboldt squid have a fairly small mouth, and their esophagus runs through their donut-shaped brain. Post-larval squid can extend their arms to grab and hold their prey. This strategy allows them to restrain and eat animals bigger than their mouths. However, creatures like whales and humans are far too large to grab ahold of.
The Humboldt squid's diet consists mainly of small fish (lanternfish, in particular), crustaceans, cephalopods, and copepods. The squid uses its barbed tentacle suckers to grab its prey and slices and tears the victim's flesh with its beak and radula. They often approach prey quickly with all 10 appendages extended forward in a cone-like shape. Upon reaching striking distance, they open their eight swimming and grasping arms, and extend two long tentacles covered in sharp hooks, grabbing their prey and pulling it back toward a parrot-like beak, which can easily cause serious lacerations to human flesh. These two longer tentacles can reach full length, grab prey, and retract so fast that almost the entire event happens in one frame of a normal-speed video camera.
Though they mostly eat micronekton - small swimming fishes, cephalopods, and crustaceans - throughout their range, Humboldt squid diets vary depending on where they live. In Mexico, they mainly eat Myctophid fishes. Commonly called lantern fishes, these small, open-ocean fishes emit light to camouflage themselves in dim waters. This camouflage strategy, called counter-illumination, is only effective at mid-depths (between 600 and 3000ft). These depths are where there is enough light that swimming organisms still cast shadows, but the amount of light is small enough that organisms can emit light of a similar brightness from their light organs. Mexican Humboldt squid also eat swimming red crabs and small squids. In California, they eat less micronekton and incorporate larger fishes such as flatfish, rockfish, hake, and even salmon into their diets.
Their behavior while feeding often includes cannibalism and they have been seen to readily attack injured or vulnerable squid in their shoal. A quarter of squid stomachs analyzed contained remains of other squid. This behavior may account for a large proportion of their rapid growth. An investigation of the stomach contents of over 2,000 squid caught outside of the Exclusive Economic Zone off the coasts of Chile found that cannibalism was likely the most important source of food. Over half had the beaks of D. gigas in their stomachs, and D. gigas was the most common prey item. Until recently, claims of cooperative or coordinated hunting in D. gigas were considered unconfirmed and without scientific merit.
Predators of Humboldt Squid
Throughout their short lives (less than two years), the Humboldt squid are hunted by predators of all sizes. Though a single female Humboldt squid can spawn millions of eggs, only a few will survive to adulthood. Many squid eggs and hatchlings become a significant, high-protein source of food for small predators. Squid that survive to adolescence and adulthood are hunted by increasingly larger predators such as tuna, sharks, dolphins, and especially sperm whales. Sometimes whole squid are found inside the stomachs of these predators and can be easily identified, but more often only their beaks remain undigested. In the last 15 years, humans have become important predators of Humboldt squid, catching and eating hundreds of thousands of tons every year.
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Human Interaction and Fisheries
As we become more influential in the trophic ecology of Humboldt squid, research in this field becomes increasingly necessary to support the sustainable exploitation of the Humboldt squid fishery. Some scientists think these squid may become more abundant and occupy a larger range, in part because they have such a flexible diet. The exact impacts of changes in Humboldt squid distribution and population size are difficult to predict. The method used by both artisanal fishermen as well as more industrial operations to catch the squid is known as jigging. Squid jigging is a relatively novel method of fishing in the Americas. It is done by handlining by artisanal fishermen, or by using mechanical jiggers. Jigging involves constantly jerking the line up and down to simulate prey; a reel with an elliptical or oval-shaped hub helps with this. Squid jigging is done at night, using bright overhead lights from the fishing boats which reflect brightly off the jigs and plankton in the seawater, luring the squid toward the surface to feed. The jigs are called poteras in Spanish. Different types of jigs are suitable for either handlining or for mechanical jigging for jumbo squid. They are made from bakelite and/or stainless steel, and measure 75 to 480 mm (3 to 19 inches) in length. Jigs can have a single axis, or one to three 'arms' (ejes) which wave around when the jig is jerked, and a series of crowns (coronas) of bristle-like wire-hooks, the hooks lacking barbs, making up the tail. The body of the jigs is usually phosphorescent, but glow-in-the-dark lures may be attached to them. Jigs are extremely selective, not only can one type of jig attract only squid, often the jigs can select for a single species of squid, and even specific sizes of that species. Based on 2009 national fisheries data, in Mexico this species represents 95% of the total recorded catch of squid.
Preparation and Consumption
Because the flesh of the animals is saturated with ammonium chloride (salmiak), which keeps them neutrally buoyant in seawater, the animal tastes unpleasantly salty, sour, and bitter when fresh. To make the squid more palatable for the frozen squid market, freshly caught Humboldt squid are commercially processed by first mechanically tenderizing them, dropping them in icy water with 1% mixture of lactic and citric acid for three hours, then washed, then soaked in another vat with a 6% brine solution for three hours. In Chile the squid is eaten in chupes and paila marina. In Peru, the practice of making ceviche from cheap squid began in the poorer parts of Lima when the meat became available in the 1990s, and has since spread to Cuzco.
Humboldt Squid and Humans
Although Humboldt squid have a reputation of being aggressive toward humans, some disagreement exists on this subject. Research suggests these squid are aggressive only while feeding; at other times, they are quite passive. Some scientists claim the only reports of aggression toward humans have occurred when reflective diving gear or flashing lights have been present as a provocation. Recent footage of shoals of these animals demonstrates a tendency to meet unfamiliar objects aggressively. Having risen to depths of 130-200 m (430-660 ft) below the surface to feed (up from their typical 700 m (2,300 ft) diving depth, beyond the range of human diving), they have attacked deep-sea cameras and rendered them inoperable. Humboldt squid have also been observed engaging in swarm behavior when met by the lights of submersibles, suggesting that they may follow or are attracted to light.
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