The North Atlantic Ocean is home to many remarkable creatures, but few are as significant for both nature and commercial fisheries as the northern shortfin squid (Illex illecebrosus). Known in Icelandic as agnsmokkur, this squid migrates vast distances and lives life at a striking pace.
Biology and appearance
Illex illecebrosus is moderate in size, with female mantles typically measuring 18–30 centimetres and males ranging from 18–27 centimetres. Its head is long and narrow, blending into a mantle that can reach up to 34 centimetres at its thickest point. The colour of this squid spans a spectrum from reddish-brown to dark purple with a dark streak along its back and a lighter, yellowish underside.
Short, equal-length arms project from the body, except for a slightly shorter reproductive arm in males. The broad fins are wider than they are long, and the angle between fin and mantle rarely exceeds 50 degrees.
A restless traveller in the ocean
Northern shortfin squid are highly migratory. Their range stretches from the Straits of Florida north to the coasts of Newfoundland, Labrador, Greenland, and across the Atlantic to Iceland and the western British Isles. Seasonal movements are pronounced: in the spring, they head to shallower continental shelf regions, while autumn sees them descending to deeper offshore waters. For example, in the Gulf of Maine, they are present inshore during summer and autumn but retreat to deeper ocean areas in winter.
They have been observed at depths of 150–275 metres near the edge of the continental shelf, with occasional appearances off Icelandic waters during certain years. Their migrations can span up to 1,000 miles, and the species moves between different ocean layers at different times of the day, coming closer to the surface at night.
This species has one of the shortest lifespans found among cephalopods, typically less than a year and rarely exceeding 1.5 years. Reproduction is year-round, although hatching occurs most frequently from June to December. Females lay gelatinous egg masses containing up to 100,000 eggs, and both sexes die soon after spawning. Growth is rapid; females tend to outpace males except in certain northern waters, where the reverse has been observed.
Juveniles measure scarcely more than a centimetre after hatching and are dispersed widely by ocean currents, while adults can reach up to 35 centimetres. Warmer waters, such as those found in the Mid-Atlantic, encourage faster growth rates.
Role in the ecosystem and fisheries
Northern shortfin squid feed on crustaceans and a variety of fish, including commercially important species like Atlantic cod and hake, sometimes practising cannibalism if the opportunity arises. Their predators include large fish such as bluefin tuna, haddock, halibut and swordfish, as well as whales, dolphins and even seabirds. Defensive behaviours include schooling, jetting ink and camouflage.
Commercial fishing for Illex illecebrosus increased significantly during the late 1970s, peaking between 1976 and 1981 in the North Atlantic. The population size can fluctuate year to year, but the species is not considered threatened. Most harvesting takes place off the coasts of the United States and Canada, where the squid gather in dense shoals suitable for trawl fishing.
Sources
- Wikipedia
- Wikipedia (Icelandic) in Icelandic
