Pacific Mackerel

The Pacific mackerel (Scomber japonicus) is a schooling pelagic fish in the family Scombridae, found along the eastern Pacific coast from Alaska to Chile, with the species also occurring widely across the Indo-Pacific under the shared name chub mackerel. It travels in large, fast-moving schools and is an important forage fish for larger predators such as tuna, sharks, and marine mammals. Pacific mackerel populations are known for significant natural boom-and-bust cycles linked to ocean temperature and productivity, historically notable for dramatic swings off the California coast. The species remains widespread and is not currently considered at risk.

Pacific mackerel share a similar body plan with Atlantic mackerel but show key differences.

• Back: iridescent blue-green with irregular, broken dark bars, less uniform than Atlantic mackerel's wavy stripes
• Lower flanks: scattered faint dusky spots, a feature Atlantic mackerel lacks
• Body: elongate, fusiform, rounded in cross-section
• Fins: two separated dorsal fins followed by 5 small finlets, plus small anal finlets
• Swim bladder: present, unlike in Atlantic mackerel
• Size: typically 25-35 cm

The spotted lower flanks and more irregular back markings distinguish Pacific mackerel from the cleaner wavy-striped pattern of Atlantic mackerel.

Pacific mackerel inhabit temperate to subtropical coastal and offshore waters of the eastern Pacific, ranging roughly from southeastern Alaska to Baja California and further south to Chile, with related populations across the Indo-Pacific. They are epipelagic, typically occurring from the surface to about 300 m, and favor waters near the continental shelf where upwelling boosts productivity. Schools move seasonally, following warm currents and prey concentrations, moving closer to shore in warmer months and offshore or southward as waters cool.

Pacific mackerel are strongly schooling fish, often forming large, fast-swimming aggregations that mix with other pelagic species such as sardines and anchovies. They feed opportunistically, filter-feeding on plankton or actively pursuing small fish and crustaceans depending on prey availability. Population abundance fluctuates dramatically over decades in response to ocean temperature regimes, a pattern well documented off the California coast. Spawning occurs in warm offshore waters, with females releasing buoyant, pelagic eggs in batches over an extended spawning season. As a key forage species, Pacific mackerel support a wide range of predators throughout the eastern Pacific food web.