Pacific Jack Mackerel

The Pacific Jack Mackerel is a schooling, open-water fish in the jack family (Carangidae), closely related to true jack mackerels of the genus Trachurus found worldwide. It ranges along the eastern Pacific from Alaska to Baja California and further offshore, forming massive schools in cool, temperate coastal and pelagic waters. Historically an important component of California Current ecosystems, it has supported large commercial fisheries at various points in the twentieth century, with populations fluctuating alongside oceanographic conditions such as El Niño cycles. It is distinguished from similar mackerel-like species by the bony lateral scutes characteristic of the jack family, and it remains widespread and abundant, with no major conservation concerns.

• Slender, fusiform, moderately compressed body
• Dark blue-green to olive back with silvery-white sides and belly
• Bony, keeled scutes forming a distinct ridge along the entire lateral line
• Two well-separated dorsal fins; small finlet near the tail base
• Forked tail with yellow-green tint
• Relatively large eye with adipose eyelid

Typically 20-30 cm, occasionally to 81 cm. The full-length row of lateral scutes reliably separates it from true mackerels (Scombridae), which lack scutes entirely, and its silvery, unmarked flanks distinguish it from more colorful reef jacks.

Pacific Jack Mackerel inhabit temperate coastal and offshore waters of the eastern Pacific, ranging from southeastern Alaska to the Gulf of California, with the largest concentrations off California and Baja California. They occupy the water column from near the surface to depths of around 400 m, often moving inshore at night to feed and offshore or deeper during the day. Juveniles frequently occur in nearshore kelp beds and bays, while adults form large pelagic schools over the continental shelf and slope. Population abundance shifts with oceanographic conditions such as sea surface temperature and current patterns, including El Niño and La Niña cycles.

Pacific Jack Mackerel are highly social, forming enormous schools that can number in the millions, moving together for feeding and predator avoidance. They undertake diel vertical migrations, rising toward the surface at night to feed on plankton and small fish and descending to deeper water during daylight hours. Spawning occurs offshore in warmer months, producing large numbers of small pelagic eggs that drift with currents. As a key forage species, jack mackerel schools support numerous predators, including larger fish, marine mammals, and seabirds, making them an ecologically critical link between plankton production and higher trophic levels in the California Current ecosystem.