Slender thread herring (Opisthonema bulleri) is found from Magdalena Bay in the Gulf of California, Mexico to northern Peru (Berry and Barrett 1963). In the north of the Gulf, in the Sonora region, this species is captured in a very low proportion (as compared to the dominant species, the Pacific thread herring - Opisthonema libertate). In the southern Gulf, in Sinaloa and Nayarit, the proportion of the three Ophistonema species is more similar, and assessment is conducted separately (Morgan et al. 2016). Through biological parameters, separate stocks have been assigned to the northern and southern Gulf of California (Ruiz Domínguez 2019). Therefore, an assessment unit is considered in Sinaloa and Nayarit in this profile for slender thread herring.

Fishery statistics in Mexico do not report catches by species because identification based on morphological characteristics is difficult and can overlap among the three species, leading to errors in identification, only being possible through genetic methods and therefore are reported as Opisthonema spp (Pérez-Quiñonez et al. 2020). Management considers the slender thread herring (O. bulleri) with two other Opisthonema species (O. libertate and O. medirastre) under the same resource: "Sardina crinuda" (DOF 2022).