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Blue Jack Mackerel
Fish Active day and night

Blue Jack Mackerel

Trachurus picturatus

iNaturalist Wikipedia

A shimmering sentinel of the Atlantic, the Blue Jack Mackerel moves in dazzling silver shoals through the coastal depths. With its streamlined body and lightning-fast reflexes, it is a master of the open water.

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Quick Identification

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Size

Commonly 25 cm (10 in), with a maximum length of 60 cm (24 in); weight up to 1.5 kg (3.3 lbs)

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Colors

Bluish to greenish-grey upper body, silvery-white belly, and a distinctive small dark spot on the gill cover

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Key Features

  • Elongated fusiform body shape
  • Highly curved lateral line with prominent bony scutes
  • Large eyes with a well-developed adipose eyelid
  • Two separate dorsal fins
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When You’ll See Them

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Activity pattern Active day and night
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Peak hours 6-9 AM, 5-8 PM
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Season Year-round
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Diet Carnivorous, primarily targeting small crustaceans like copepods, as well as fish larvae and small fry.
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Habitat Coastal waters, continental shelves, and upper slopes reaching depths of 370 metres.

Behavior

The Blue Jack Mackerel is a highly social, shoaling fish that moves in large, tightly packed groups to deter predators. They are benthopelagic, meaning they spend much of their time near the seafloor but frequently rise through the water column to feed. This species exhibits a pronounced diurnal vertical migration, staying in deeper, cooler waters during the day and ascending toward the surface under the cover of darkness.

In their interactions with humans, they are primarily known as a commercial and game fish. While they do not show complex social hierarchies, their synchronized swimming is a marvel of collective behavior, allowing the shoal to act as a single, shimmering organism to confuse hunters like tuna, dolphins, and seabirds.

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Camera Tips

Capturing the Blue Jack Mackerel requires specialized underwater equipment, as they are rarely found in the shallowest tide pools. If you live near a coast or have access to a pier, mounting an underwater action camera to a weighted tripod or a submerged pylon is the best way to see them. Position your camera to face slightly upward toward the light; this 'silhouetting' technique makes it much easier to see the mackerel’s sleek profile and the movement of the shoal against the brighter surface water.

To attract these fast-moving fish to your camera’s field of view, use a scent-based lure or 'chum.' A mesh bag filled with oily fish scraps, like sardines or mackerel, secured a few feet from the lens will create a scent trail that draws them in. Additionally, Blue Jack Mackerel are attracted to visual stimuli; adding a small, shiny metal spinner or a reflective 'flash' tape near the bait can mimic the shimmer of a panicked baitfish, triggering their predatory instincts and bringing them right in front of the sensor.

Because water absorbs light quickly, especially the red end of the spectrum, your footage may appear very blue or green. If your camera setup allows, use a red filter or external underwater video lights to bring out the natural silver and blue hues of the fish. Since they are most active during the 'change of light' at dawn and dusk, ensure your camera is set to a high frame rate (at least 60fps) to avoid motion blur, as these fish are incredibly fast and change direction in the blink of an eye.

Similar Species

Species that look similar or are commonly confused with Blue Jack Mackerel.

Atlantic Horse Mackerel

Features a deeper body profile and a more dramatic, steep drop in the lateral line near the pectoral fin.

Mediterranean Horse Mackerel

Smaller on average with an accessory lateral line that ends much earlier than the Blue Jack's.

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Frequently Asked Questions

They are most active during dawn and dusk (crepuscular periods) when they move between deep and shallow water to feed, though they can be spotted throughout the day in deeper shoals.
Use oily fish bait like sardines in a mesh bag and add reflective metal lures. They are attracted to both the scent of prey and the shimmer of moving objects.
Their diet consists mainly of zooplankton, such as copepods and other small crustaceans, along with the larvae of other fish.
They are strictly marine fish, so you'll only find them in coastal areas, often near man-made structures like deep-water piers, jetties, and marinas.
The Blue Jack Mackerel has a more slender body and its lateral line stays high and curved for longer before dropping, whereas the Atlantic Horse Mackerel's line drops more abruptly.

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