Longspine thornyhead (Sebastolobus altivelis) are found from the southern tip of Baja California, Mexico, to the Aleutian Islands but are abundant from Southern California northward (Medley et al 2014).

Population genetic studies based on mitochondrial DNA sequences (mtDNA) support the prediction of wide ranging dispersal with little to no geographic population diversity off the US west coast. For modelling purposes, one stock of longspine thornyhead was assumed to exist in the assessed area. It is unlikely that there are significant interactions across the northern (US/Canada) and southern (US/Mexico) boundaries of the stock unit, thus, this species is managed as a single stock within the US EEZ from the Canadian to Mexican border (Fay 2005).