The secret love life of the longfin squid

Squid have occupied New England’s maritime imagination for centuries, from fishermen’s tales of strange tentacled creatures to the widely publicized giant squid reports along North Atlantic coastlines in the 1800s. Today, we turn a curious eye toward the longfin inshore squid (Doryteuthis pealeii) — the “Boston squid” — which has long been an important part of regional commercial fisheries. These squid thrive in the emerald green depths off the coast of Massachusetts, where low visibility is characteristic of the turbid, nutrient-rich waters.

Keith Ellenbogen, MIT Sea Grant resident artist and acclaimed underwater photographer, knows these waters well. On a good day, he might have 20 feet of visibility beneath the surface. But even with the clearest conditions, these swift squid evaded Ellenbogen’s lens for months. 

In 2023, over 2.85 million pounds of longfin squid — likely over 6 million individual squid — were landed commercially in Massachusetts, with a value exceeding $2.82 million. Consistently among the top 10 species landed commercially in Massachusetts, the longfin squid shares the ranks with the iconic American lobster, Atlantic surf clam, and sea scallop, underscoring its enduring significance in the state’s seafood industry. 

In 2024, landings came in under 750,000 pounds, roughly a quarter of the previous year’s catch. Likewise, the spring 2024 trawl survey documented in the Massachusetts Division of Marine Fisheries Annual Report recorded a historic low in longfin squid biomass, following a record high in 2023. 

But this drop, while significant, doesn’t necessarily spell trouble for the species. Longfin squid often show large fluctuations in abundance from year to year. Their short lifespan of about six to nine months, combined with their sensitivity to shifting ocean conditions, makes their population dynamics inherently unpredictable. 

Kimberly Hyde, a biological oceanographer with the National Oceanic and Atmospheric Administration (NOAA)’s Northeast Fisheries Science Center (NEFSC), notes that NEFSC research scientists have expanded squid research over the past few years, including a two-year study on longfin squid to better understand their life history and track their maturity and readiness to spawn. Across the Northeast, scientists are also collaborating with the fishing industry through efforts including the Longfin Squid Biological Sampling Program (SQUIBS), Collaborative SQUid Size Monitoring (SQUISM), and the Squid-Squad, a highly interdisciplinary team of scientists, industry members, and managers with a common goal to improve squid science. Still, much of this cephalopod’s story remains hidden from sight. 

After years of trying to find and photograph a squid spawning aggregation, Ellenbogen chartered a vessel and worked with a network of local fishermen to locate concentrations of squid beneath the surface. In New England’s emerald-green, nutrient-rich coastal waters, visibility was limited, and although he knew he was directly above the spawning grounds, finding a cluster of eggs and squid 30 to 40 feet below the surface was far from easy.

“As I descended through the emerald-green waters of Cape Cod, I couldn’t see anything at first,” Ellenbogen recalls. “I knew I was in the right area, but the seafloor seemed empty. Then I noticed a few faint shadows moving in the distance.” 

As he swam closer, the scene slowly revealed itself. 

“First came the squid, then the egg masses, and then hundreds more animals appearing out of the green water. Suddenly I found myself surrounded by squid flashing colors, courting, competing, and spawning,” Ellenbogen says. “It felt like being in a theater, watching a carefully choreographed performance unfold all around me.”

Dozens of squid hovered intently in a circle with arms and tentacles stretching toward the focus of attention: a large pale cluster of eggs fixed to a bed of slipper shells and fingerlike seaweed. Thousands of gelatinous, translucent egg capsules swayed softly in the current. Male and female pairs broke from the outer circle with ceremonial precision, darting inward to spawn. Their alienlike bodies pulsed and flickered with waves of color, from flares of rust-red, golden yellow, and iridescent pink to flashes of lightning white. Their brief lives had culminated here in this critical moment of coordination to give rise to the next generation. 

Longfin squid live fast and die young, exhibiting incredible exponential growth throughout their lifespan of less than one year. They emerge from egg capsules as planktonic hatchlings — paralarvae — that already look like tiny 1.5 millimeter simplified versions of their adult form. 

Still small but fast-growing, juveniles feast on planktonic prey in coastal, surface waters and move deeper in the water column as they grow larger, settling on a life closer to the seafloor. As natural-born ambush and pursuit predators, they begin hunting small crustaceans and other invertebrates — including other squid — with jet propulsion and 10 grasping arms and tentacles.

Like octopuses, squid have chromatophore organs, pigmented cells controlled by nerves and muscles through their central nervous system. Contraction or dilation of these sacs results in mesmerizing iridescence and color shifts. Their color-changing behavior serves several purposes, including camouflage, courtship, and communication through ancient visual language. And to add an extra layer of curiosity, squid themselves are effectively colorblind. Their eyes are well-adapted to detect contrast, brightness, movement, and even polarization, but not to perceive hues like we do.

According to a report from the NEFSC, longfin squid can reach sexual maturity at a mantle length of just 8 centimeters. Nearing adulthood, they migrate offshore to overwinter in deeper, warmer waters along the continental shelf. At night, they form large schools grouped by body size and move upward in the water column to feed. Growth remains rapid and temperature-dependent, with males growing faster and larger than females.

Longfin squid spawn year-round with seasonal and geographic peaks. In New England waters, spawning has been reported from May to August. Egg clusters, or mops, like the one Ellenbogen photographed, act like a hub. As reported by NOAA Fisheries, female squid lay fertilized egg capsules that contain about 150 to 200 eggs each in clusters attached to the ocean bottom. They return repeatedly to deposit multiple clutches of eggs over several weeks, with a typical female laying a total of 3,000 to 6,000 eggs.

Spawning typically occurs in seasonal pulses tied to water temperature and other conditions, sometimes triggering large spawning aggregations — dense gatherings of squid depositing and fertilizing eggs. Males and females gather in the spawning grounds, and density increases until individuals are constantly interacting.

But reproductive biology and behavior are complicated for longfin squid. The NEFSC report highlights unique behavior: Females can store sperm from spawning events for later use, and eggs in the same capsule from a single female may have multiple males from multiple spawning events. 

Consort males, typically the larger males, pair up with a single female during spawning. They swim closely alongside her, often guarding her with their arms, and use their size to intimidate competition. Sneaker males, smaller unpaired squid, use stealth and speed to sneak into position with paired females. Males deposit bundles of spermatophores into the female’s mantle cavity or in a pouch located near her head. 

The competition is guided by visual and chemical signals, including pheromones indicating reproductive readiness, rapid color and pattern changes, as well as strategic arm postures and whole-body displays. A 1999 paper published by the Marine Biological Laboratory catalogued 34 visual displays involving colors, brightness, spots, stripes, iridescence, and polarization signals, as well as 17 specific positions and movements used by squid on the spawning grounds. 

Squid were seen flashing white as a signal to repel other squid. Squid displaying this component are almost always engaged in mate guarding, egg laying, or competitive confrontations. Like humans, female squid can blush, displaying a dark patch on one side of the mantle. But when a squid blushes, it functions as a repellent to courting males. And as captivating as these colorful displays can be, squid communication largely remains an encrypted secret to even the most curious scientists. 

“Keith’s rare glimpse of squid in their natural environment beautifully bridges art and science, reminding us that we still have much to learn,” says Hyde, who has centered her research at NOAA on marine ecosystems and fisheries. 

For most people, squid are known solely as seafood or as shadowy legends, chameleons of the sea. Yet each spring, beneath the cool waters of Cape Cod, millions of longfin squid gather in this remarkable reproductive event, a reminder of the rich biodiversity and productivity of Massachusetts marine ecosystems. 

MIT Sea Grant works to support sustainable fisheries and to promote environmental education and stewardship of our coastal and ocean resources. As MIT Sea Grant’s resident artist, Keith Ellenbogen is working on a long-term project to document extraordinary species and ocean events that unfold just off our coast, revealing hidden moments that few have the opportunity to witness. The longfin squid is one of our region’s most valuable marine resources, and these images help reveal one of the most extraordinary events unfolding right off our coast.