Flatiron Herring, Harengula thrissina

Flatiron Herring, Harengula thrissinas. Fish provided by the commercial fishermen of Puerto Los Cabos, Baja California Sur, September 2015. Length: 18 cm (7.1 inches).

The Flatiron Herring, Harengula thrissina, whose common Spanish name is sardina plumilla, is a member of the Herring or Clupeidia Family, and known in Mexico as sardina plumilla or just “sardina.” There are four global members of the genus Harengula, and all four are found in Mexican waters, three in the Atlantic and one in the Pacific Ocean.

The Flatiron Herring has a moderately deep fusiform compressed body with a depth that is 27% to 31% of standard length. Both their upper and lower body profiles are convex. They are iridescent blue dorsally and silvery on their sides with a faint yellow stripe on their upper sides and a black spot behind their gill covers. Their mouth opens at the front with a slightly projecting lower jaw. Their anal fin has a short base and 15 to 17 rays with its origin being well behind the dorsal fin; their caudal fin is deeply forked; their dorsal fin is located mid-body with 17 or 18 rays; their pectoral fins reach the dorsal origin; and, their pelvic fins are located directly under the dorsal fin. They have 28 to 34 gill rakers. Their body is covered with scales.

The Flatiron Herring is a pelagic coastal schooling species that form very large schools found near and within protective rock cover on the surface in the surf zone at depths up to 8 m (25 feet). They reach a maximum length of 18.0 cm (7.1 inches) and are virtually weightless. The Flatiron Herring is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Flatiron Herring is a resident of all Mexican waters of the Pacific with the exception that they are absent from Guerrero Negro, Baja California, northward along the central and northwest coasts of Baja.

The Flatiron Herring is very similar to the False Pilchard, Harengula clupeola (found only in the Atlantic Ocean). It is a straightforward identification that cannot be confused with any other sardine or herring of the Pacific due to its wide body and lack of elongated dorsal fin rays.

From a conservation perspective the Flatiron Herring is currently considered to be of Least Concern with stable, widely distributed populations. They are not fished commercially and only sold as a “live bait” when available.

Note: this species is routinely referred to as “sardina” or “sardine.” This small beast is THE mainstay of the live bait industry in the Los Cabos area. As a rule of thumb if you have sardines in your Panga you will have a highly productive day and if you don’t you won’t! Having said that, this species virtually disappeared from the greater Los Cabos area from 2011 to 2018. In 2019 they have made a small come back but were only present on random days in random locations. In 2020 they have disappeared again.