1. How Researchers Filmed a Living Giant Squid in 2004
Before 2004, giant squids were only known from dead specimens that had washed ashore or been caught by accident during fishing. No one had seen one swimming alive. In 2004, researchers lowered a camera baited with food into the sea off the Ogasawara Islands. A giant squid appeared, and the team successfully filmed it [1].
The squid in the video had a mantle (body length) of about 1.7 meters (about 5.6 feet). Its body length including arms was 4.7 meters (about 15.4 feet). The total length, including the long tentacles, is estimated to be over 8 meters (about 26 feet) [1]. Later studies suggest that giant squids likely feed in the middle depths, between 650 and 900 meters (about 2,100 to 2,950 feet), during the day. Evidence shows they eat small cod-like fish, and they may also eat smaller squids [1].
2. How Big Do Giant Squids Really Get? Checking the 20-Meter Claim
You may hear stories about giant squids reaching 20 meters (about 65 feet). However, these records have not been scientifically verified [2]. Recent estimates put the maximum length of females, measured from the back of the fins to the tip of the arms, at about 5 meters (about 16 feet). With their long tentacles stretched out, they may reach about 10 meters (about 33 feet) [2].
On the other hand, a statistical analysis published in 2016 suggests that sizes of 10 meters or even 20 meters are "possible" [3]. Experts do not agree on the maximum size. A major reason for the differing numbers is that measurements are recorded differently. Mantle length, body length including arms, and total length including tentacles cannot be compared directly. Also, female giant squids tend to be larger than males, which adds to the range of reported sizes [2].
3. Why Deep-Sea Gigantism Does Not Apply to Every Deep-Sea Animal
The phenomenon where deep-sea animals grow larger than their shallow-water relatives is called "deep-sea gigantism." However, not every creature in the deep sea is big. Examples of animals that grow large include crustaceans like amphipods and isopods, shrimp, cephalopods like squids and octopuses, jellyfish, and eels [4].
For instance, the giant amphipod (Alicella gigantea) has an adult body length of 240 to 340 millimeters (about 9.4 to 13.4 inches). Most amphipods are less than 40 millimeters (about 1.6 inches) long, making the giant species more than six times larger [5]. Conversely, very small creatures called meiofauna, which are less than 1 millimeter long, tend to get smaller as the water gets deeper [4]. Size is not determined by depth alone; it varies by species.
4. Four Possible Explanations for Why Deep-Sea Animals Grow Large
There are several hypotheses for why deep-sea gigantism occurs. These theories do not necessarily contradict each other; some may work at the same time [4].
First, cold water may lead to larger bodies and longer lives. The idea is that lower temperatures cause cells to grow larger and extend lifespan. This is an extension of Bergmann's rule, which states that animals in colder climates tend to be larger [4]. Second, higher dissolved oxygen levels may allow for larger bodies [4]. Third, in environments with little food, a larger body may be advantageous because it allows the animal to travel farther to find food [4]. Fourth, if there are fewer predators, a large body is less likely to be targeted [4]. It is not decided which theory is the most important. Different species may fit different theories.
5. Testing the Predator Theory With Scars on Brachiopod Shells
The idea that there are fewer predators in the deep sea is common. One study tested this by looking at brachiopods, shell-like animals. Researchers counted the number of healed bite scars on their shells [6].
The study found that the frequency of healed scars decreased logarithmically with depth. Below 200 meters (about 656 feet), there was no difference based on latitude [6]. This result supports the idea that predation is lower in the deep sea. However, the study focused on brachiopods and did not directly verify why animals grow larger.
6. Do the Four Theories Explain the Giant Squid's Size?
The first theory suggests that cold water leads to long life and large size. Does this apply to the giant squid? Giant squids grow quickly and are thought to have short lifespans. Estimates based on growth rings in their beaks (similar to tree rings) suggest an age of 411 to 674 days, which is about 1 year and 1 month to 1 year and 10 months. Some research estimates the largest individuals live for about 3 years [7].
However, there is no consensus on their lifespan. Some estimates suggest 2 to 3 years, while others suggest more than 25 years [7]. If the lifespan is short, the theory that "they are big because they live long" does not fit well for giant squids. This is an inference from the data, not a confirmed fact. Other theories, such as scarce food or few predators, might apply better to them.
7. Measuring a Giant Squid's Length With String and a Tape Measure
If you want to understand the size better, you can try measuring it. Use a string and a measuring tape in a wide space to measure 8 meters (about 26 feet). Choose a wide, traffic-free place, such as a park or schoolyard, and go with an adult. The filmed squid was 8 meters long in total, but its body (mantle) was only 1.7 meters (about 5.6 feet). This shows how much the number changes depending on what part of the squid you measure [1].
You can also visit aquariums or science museums, which sometimes display giant squid specimens or photos. Exhibits change over time, so check the official website before you go. The National Museum of Nature and Science has information summarizing the 2004 filming and later findings [1].