Splitnose rockfish (Sebastes diploproa) are distributed from the northern Gulf of Alaska (Prince William Sound) to central Baja California and occur at depths between 91-795 meters. Adults are the most abundant between British Columbia and southern California at depths from 215 to 350 meters (Alverson et al. 1964, Gunderson and Sample 1980, Love et al. 2002).

Splitnose rockfish co-occur with an assemblage of slope rockfish, including Pacific ocean perch (Sebastes alutus), darkblotched rockfish (Sebastes crameri), yellowmouth rockfish (Sebastes reedi), and sharpchin rockfish (Sebastes zacentrus) off Washington and Oregon, and striptail rockfish (Sebastes saxicola), darkblotched rockfish and shortspine thornyhead (Sebastolobus alascanus) off central California. 

This species is explored commercially off the continental coast of the United States from the U.S.-Canadian border in the north to the U.S.-Mexican border in the south. Splitnose rockfish have been caught primarily in fisheries for mixed slope rockfish or other deepwater targets.

Belonging to a multispecies complex fishery, this rockfish is not consistently sorted to species, and landings are estimated from applying port sampling species compositions to mixed rockfish landings. Trawl landings on average comprise 90% of annual catches, with 80% of fish landed in California. Only 10% of splitnose rockfish on average are caught by non-trawl commercial fisheries. The vast majority of non-trawl landings are caught by net gear, and only a small portion is caught by hook-and-line in the sablefish fishery. This species is rarely taken in the recreational fishery (Gertseva et al. 2009).

There are no clear stock delineations for splitnose rockfish in the U.S. waters. No molecular markers have yet been developed for this species, and no genetic data are currently available to suggest the presence of several stocks (Waples et al. 2008). Within the assessment area the resource is treated as a single stock due to the lack of biological and genetic data supporting the presence of multiple stocks. Nevertheless, management decisions on a coast-wide population need to account for effort concentration, since abundance is higher in some areas such as off central California.

Splitnose rockfish were historically managed within the Sebastes complex. In 1994, the Sebastes complex was divided into southern (Conception, Monterey and Eureka INPFC areas) and northern (Columbia and US Vancouver INPFC areas) management areas, and harvest guidelines were established for the complex in each area (Gertseva et al. 2009).

In 1999, the general Sebastes complex was divided into near-shore, shelf, and slope assemblages, and the dividing line between the northern and southern management units was shifted southward to 40o 10’ N. latitude, near Cape Mendocino.