Pacific Menhaden

The Pacific Menhaden, also known locally as machuelo, is a deep-bodied clupeid fish found along the Pacific coast of South America, primarily off Peru and Chile within the Humboldt Current system. Classified in the monotypic genus Ethmidium, it is a filter-feeding coastal pelagic species ecologically similar to the menhaden of the Atlantic, though only distantly related. The species forms large schools in the highly productive upwelling waters of the Humboldt Current, where it feeds on abundant plankton alongside the more numerous Peruvian Anchoveta. Pacific Menhaden serve as an important secondary forage species supporting seabirds, marine mammals, and predatory fish along the South American Pacific coast.

Field marks:

• Deep, laterally compressed body with a proportionally large head
• Strongly silvery flanks with a greenish to bronze back
• Row of dark spots running along the mid-flank, distinct from the single large shoulder spot of Atlantic Menhaden
• Sharp scutes along the belly midline
• Single dorsal fin, deeply forked tail
• Adults typically 20-36 cm

Pacific Menhaden are distinguished from the smaller, more slender Peruvian Anchoveta by their deeper body and larger size, and from Atlantic Menhaden (a different genus found in a separate ocean basin) by their row of evenly sized flank spots rather than one dominant shoulder spot.

Pacific Menhaden inhabit coastal waters along the Pacific coast of South America, primarily off Peru and northern-to-central Chile, within the cold, nutrient-rich Humboldt Current upwelling system. They are typically found in the upper water column over the continental shelf, favoring productive coastal zones where upwelling sustains high plankton density. The species' range and abundance fluctuate with oceanographic conditions, including periodic El Nino events that reduce upwelling intensity and disrupt local food availability. It often schools alongside or near Peruvian Anchoveta in similar coastal habitat.

Pacific Menhaden are filter feeders, swimming through plankton-rich water with mouths open to strain phytoplankton and zooplankton using fine gill rakers, a feeding strategy well suited to the highly productive Humboldt Current. They form coordinated schools in coastal waters, often in proximity to the far more numerous Peruvian Anchoveta, with which they share habitat and food resources. Populations respond to oceanographic variability, contracting during warm, low-productivity El Nino periods and expanding during strong, cool upwelling phases. Spawning occurs in coastal waters, with eggs and larvae dispersing with nearshore currents. As a secondary forage species within the Humboldt Current ecosystem, Pacific Menhaden contribute to the diet of seabirds, marine mammals, and larger predatory fish.