Pacific thread herring (Opisthonema libertate) is found from San Pedro, Southern California, USA and the Gulf of California, Mexico to northern Peru, including Galapagos Islands (CGSDM, 2013). According to Bakun et al. (2009), the Gulf of California is intermittently subject to important influxes and major exchanges of small pelagic forage fishes, such as Opisthonema libertate, both northwards and southwards the mouth of the Gulf. Recent studies based on body shape, otolith shape, populations size structure, growth pattern and length-weight relationship suggest the existence of different phenotypic stocks in the coasts of Sonora, Sinaloa-Nayarit and the West coast of the Peninsula of Baja California (Perez Quinonez et al. 2018)(Ruiz Domínguez 2019).

Pacific thread herring or Sardina crinuda (Opisthonema libertate) is very similar morphologically to two other local species, Slender thread herring or Sardina crinuda azul (Opisthonema bulleri) and Middling thread herring or Sardina crinuda machete (Opisthonema medirastre), also retained by the small pelagic fishery in the southern Gulf of California (SAGARPA, 2012a). Even though these are recognized separately in the fishery management plan, catch records are still pooled together in the fishery reports (SAGARPA, 2013).