Flatiron Herring, Harengula thrissina
The Flatiron Herring, Harengula thrissina, whose common Spanish name is sardina plumilla, is a member of the Herring or Clupeidia Family, known collectively as sardinas in Mexico. There are only four global members of the genus Harengula, and all four are found in Mexican waters, three in the Atlantic and one in the Pacific.
The Flatiron Herrings have moderately deep fusiform compressed bodies 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. They have 28 to 34 gill rakers. 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. Their body is covered with scales.
The Flatiron Herrings are 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 25 feet. They reach a maximum length of 18.0 cm (7.1 inches) and are virtually weightless.
In Mexican waters the Flatiron Herrings are found in all waters of the Pacific with the exception that they are absent from Guerrero Negro northwaed 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 cannot be confused with any other sardine or herring of the Pacific due to its wide body and lack of elongated dorsal fin rays.
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 2016.