Fish crepuscular

Chilean jack mackerel

Trachurus murphyi

A titan of the South Pacific, the Chilean jack mackerel is a master of synchronized swimming and a cornerstone of the marine food web. Known for its shimmering silver scales and incredible migratory journeys, this schooling specialist is a marvel of oceanic endurance.

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Quick Identification

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Size

Typically 45-70 cm (18-28 inches) in length; weighs between 0.8-2.5 kg (1.8-5.5 lbs).

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Colors

Metallic blue-green to dark grey on the dorsal surface, transitioning to a shimmering silver-white on the belly and sides.

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Key Features

Streamlined, fusiform body shape
Prominent bony scutes (plates) along the entire length of the lateral line
Distinctive black spot on the edge of the operculum (gill cover)
Two dorsal fins with a deeply forked caudal fin

When You’ll See Them

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Activity pattern crepuscular

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Peak hours Dusk and dawn, with significant surface activity throughout the night.

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Season Year-round, but most active near coastal regions during summer upwelling months.

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Diet Carnivorous and opportunistic; primarily feeds on zooplankton, small crustaceans (like krill), and small fishes such as anchovies and sardines.

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Habitat Pelagic zones of the South Pacific, often associated with coastal upwelling regions and offshore oceanic waters.

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Behavior

The Chilean jack mackerel is a highly social, pelagic species known for forming massive, tight-knit schools that can extend for miles. These schools are a survival strategy, designed to confuse predators such as sea lions, tuna, and sharks through a shimmering, synchronized mass of movement. They are nomadic travelers, following the nutrient-rich waters of the Humboldt Current and the broader South Pacific 'Jack Mackerel Belt.'

As a species heavily impacted by commercial fishing, their behavior has shifted in response to population pressures. They are known for diel vertical migration, staying in deeper, cooler waters during the day to avoid visual predators and rising toward the surface at night to feed. While they generally avoid human contact, they are often found congregating around offshore platforms or large coastal piers where artificial lights attract their prey.

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Camera Tips

To capture the Chilean jack mackerel on an AI-powered camera, you will need a specialized underwater housing or a drop-camera system. For those with coastal access or docks, mounting your camera 2-5 meters below the surface near a structural piling is ideal. Because these fish are attracted to the periphery of light, positioning a submersible LED light about 3-4 meters away from the lens can create a 'stage' that draws in the plankton and small fry they hunt, eventually bringing the mackerel into the frame.

Since mackerel are fast-movers, set your camera to a high frame rate (at least 60fps) and a fast shutter speed to avoid motion blur in the underwater environment. If your AI camera supports motion-triggering, adjust the sensitivity to high, as the silver flashes of a passing school can be brief but intense. Avoid placing the camera in areas with heavy kelp or debris, as the movement of vegetation will cause false triggers in the surging current.

Baiting can be highly effective for bringing schools within range of a stationary camera. Using a 'chum bag' filled with oily fish scraps or crushed sardines suspended just above the camera's field of view will create a scent trail. The most dramatic footage is often captured during the 'change over' periods—just as the sun sets or rises—when the fish move vertically through the water column and their metallic scales catch the ambient light.

Similar Species

Species that look similar or are commonly confused with Chilean jack mackerel.

Pacific Chub Mackerel

The Chub mackerel has dark, wavy lines on its back and lacks the prominent bony scutes along the lateral line found on the Jack mackerel.

Yellowtail Amberjack

Yellowtails are much larger and heavier, with a distinct yellow stripe running from eye to tail and lacking the Jack mackerel's scutes.

Frequently Asked Questions

They are most active during the crepuscular hours of dawn and dusk, though they frequently rise to the surface at night to feed on plankton.

As an oceanic fish, they won't visit a traditional backyard, but if you have a coastal dock, you can attract them using submersible green lights and fish-based chum bags.

Their diet consists mainly of small crustaceans like krill, various zooplankton, and smaller schooling fish like anchovies.

No, they are strictly marine fish found in the open ocean and coastal waters of the South Pacific, particularly off the coasts of Chile and Peru.

Look for the row of sharp, bony plates (scutes) along the entire length of their lateral line and the specific black spot on their gill cover.

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