Abbreviated Life History of Grass Rockfish
(Sebastes rastrelliger)

Grass Rockfish; Photo by Steve Lonhart of Simon/NOAA

Grass rockfish are heavy-bodied, stubby, spiny fishes. The coloring is dark green to olive green with black or gray mottling. They somewhat resemble kelp rockfish except that kelp rockfish are usually brown or gray-brown and kelp have long gill rakers, whereas grass rockfish have short gill rakers. There is also a rare light-colored variation in pigmentation that is yellowish-orange.

Distribution, Stock Structure and Migration

Grass rockfish are found from Yaquina Bay, Oregon to Bahia Playa Maria, central Baja California, although they are most common from northern California south. This is a shallow water species, commonly found from the intertidal to 20 ft, but they have also been found to depths of 150 ft. As juveniles they are pelagic, but as they mature and become adults, they associate with kelp beds and reefs. Juveniles and subadults can be found in tide pools. This species is considered residential, moving less than a meter from its home range.

Age and Growth

Grass rockfish have been aged to a maximum of 23 years, and males and females grow at about the same rate and reach a similar maximum size . Based on a calculated age-length relationship, an 11.5-in. TL grass rockfish is approximately 5 yr old, a 16-in. TL fish is approximately 10 yr old, and an 18-in. TL fish is approximately 14 yr old. Maximum length recorded for this species is 22 inches.

Reproduction, Fecundity and Seasonality

Male and female grass rockfish reach first maturity at different lengths and ages. In southern California, a few fish mature at 8.6 inches (2 years), 50 percent are mature at 9.4 inches (4 years), and all are mature at 11 inches (5 years). The smallest mature female off central California was 11.7 inches and the largest immature fish was 13.0 inches. The smallest mature male was 14.4 inches and the largest immature male was 17.3 inches. Females produce between 80,000 and 760,000 eggs per season and release all larvae at the same time.

In southern California waters, spawning takes place between January and March with peak spawning in January. Limited sampling in central California shows that peak spawning occurs in January as well. When first released, the larvae are between 0.17 and 0.18 in. SL and after 2 months, they settle out of the plankton at about 1.1 inches. Young-of-the-year first appear in shallow waters between spring and summer.

Predator/Prey Relationships

Larval grass rockfish are diurnal feeders, but as adults they are nocturnal feeders. Juveniles and adults prey upon crustaceans, but the adults also eat other fish (such as juvenile surfperches and midshipmen). Predators of juveniles include birds, porpoises, and fishes, including rockfishes, lingcod, cabezon, and salmon. The adults are prey of sharks, dolphins, and seals.

Competition

Grass rockfish, commonly occurring in kelp beds and reef structures, may compete for space and food with other demersal fishes common to these habitats such as cabezon, lingcod, greenlings, and other rockfish such as gopher, black-and-yellow, China, quillback, copper, and vermilion. Among rockfishes, they share a fairly narrow depth distribution primarily with the black-and-yellow rockfish. Research using mitochondrial DNA suggest that grass rockfish may be most closely related to calico and brown rockfishes.

Critical Habitat

Grass rockfish are a shallow water species, most commonly found from the intertidal to 20 ft, but usually only the juveniles are found in tide pools. Among rockfishes, they have one of the shallowest and relatively narrow depth ranges. They are found in vegetated areas, particularly kelp beds, and around reef structures where the adults may be found hiding in crevices.

Fishery and Status of Stocks

In the twentieth century and until 1990, grass rockfish were rarely landed in the commercial fishery. They became sought-after because of their proximity to shore and their hardiness once the live-fish fishery boomed in the early 1990s. Grass rockfish are taken in substantial numbers by finfish traps and commercial hook-and-line, particularly in central California. They also make up a substantial portion of the shore-based recreational fishery, where they are taken by both divers and anglers.

No formal stock assessment has been completed for this species. Currently, grass rockfish are managed as part of the Nearshore Rockfish category.

Information on this page was originally presented in the Nearshore Fishery Management Plan (these profiles updated July, 2010).

Grass Rockfish