Fish
Atlantic Mackerel
Scomber scombrus · also called Boston mackerel, Scotch mackerel
The Atlantic mackerel is a small, beautiful, restless fish: a blue-green torpedo scribbled with black bars, moving through the open North Atlantic in fast schools that never stop. It is also one of the most important food fish of the region, and the centre of a decades-long argument over who is allowed to catch how much of it.
Overview
Scomber scombrus is a member of the same family as the tunas, built as a smooth spindle with a deeply forked tail and a row of small finlets before it. The back is iridescent blue-green crossed by 20 to 30 wavy dark bars; the belly is silvery white. It has no swim bladder, so it must swim continuously to stay off the bottom and to keep water flowing over its gills.
A plankton-strainer that can also chase
For most of the year the mackerel feeds on copepods and other plankton, sieving them from the water with fine gill rakers when they are abundant. When they are not, it switches to actively hunting small fish such as sand eels. Its huge, size-sorted schools move inshore and north in spring to feed and spawn, then retreat to deep water along the shelf edge for winter.
On the plate, and in the news
Mackerel is an oily, omega-3-rich food fish, eaten fresh, smoked, and canned, and it is fished on an enormous scale. Because its flesh spoils fast, generating histamine that causes scombroid poisoning, freshness is critical. The northeast Atlantic stock is healthy in itself, but the coastal states that fish it have never agreed on quota shares, so total catches have repeatedly overshot scientific advice.
Status
The Atlantic mackerel is Least Concern. The stock is not biologically overfished, though its size fluctuates and the unresolved international quota dispute remains a management concern.
Atlantic Mackerel: common questions
Why does a mackerel have to keep swimming?
Two reasons, both to do with how streamlined it is. First, unlike most bony fish the Atlantic mackerel has no swim bladder, the gas-filled organ that provides neutral buoyancy, so if it stops swimming it slowly sinks. Second, it relies partly on ram ventilation, meaning it breathes by keeping its mouth slightly open and letting its forward motion push water over the gills, rather than actively pumping water the way a resting fish does. A mackerel held still in a net or a bucket quickly runs short of oxygen. This lifestyle, shared with tuna and some sharks, is the price of a body shaped for speed and endurance in open water.
Is Atlantic mackerel healthy to eat, and is it sustainable?
Nutritionally it is one of the better fish choices, being rich in long-chain omega-3 fats, protein, vitamin D, and B vitamins, while sitting lower in the food chain than large predators, so it carries less mercury than tuna or swordfish. On sustainability the picture is more mixed. Atlantic mackerel is not overfished in the biological sense and the stock is in reasonable shape, but for years the countries that fish the northeast Atlantic stock, including the European Union, the United Kingdom, Norway, Iceland, and the Faroe Islands, have failed to agree on quota shares, so the combined catch has repeatedly exceeded the total that scientists advise. Several eco-labels have suspended or downgraded their mackerel ratings as a result.
Why can mackerel make you ill if it is not fresh?
Mackerel, tuna, and other members of the same family have unusually high levels of the amino acid histidine in their muscle. After the fish dies, bacteria that are naturally present begin converting that histidine into histamine, and this happens quickly at room or fridge-door temperatures. Histamine is not destroyed by cooking or canning, so a fish that was mishandled before it was processed can still cause a reaction. The illness, called scombroid or histamine poisoning, brings flushing, headache, a peppery taste, stomach upset, and sometimes a rash within an hour of eating, and it usually passes within a day. Prompt, thorough chilling of the catch prevents it.
How is a mackerel different from a tuna?
They are close relatives in the same family, the Scombridae, and share the streamlined body, the finlets before the tail, and the need to keep moving. The main differences are size and warmth. A tuna is far larger, from a few kilograms up to hundreds in the bluefin, while an Atlantic mackerel rarely exceeds half a metre and about a kilogram. Tuna are also partly warm-bodied, using a heat-exchange system to keep their muscles, eyes, and brain above water temperature for sustained high-speed hunting, whereas the mackerel is cold-bodied like most fish. In the water a mackerel school is a shimmer of small barred fish; a tuna is a heavy solitary or small-group predator.