Serranoides is a combination of Latin and Greek that means "resembling a bass." Fishermen in southern California refer to this fish as “jonny bass”. Olive rockfish are one of several nearshore Sebastes associated primarily with the midwater region of kelp forest of the California coast. They are streamlined fish with almost no head spines. Their body color is dark brown or dark green-brown on the back and light brown or green-brown on the sides.
Distribution, Stock Structure and Migration
Olive rockfish occur from southern Oregon to Islas San Benitos (central Baja California) from surface waters to 570 ft. They are common from about Cape Mendocino to Santa Barbara and around the northern Channel Islands from surface waters to about 570 ft.
Tagging studies have found that olive rockfish move relatively little, ranging from less than one mile. This species has been variously described as transient or residential.
Age and Growth
Ageing of otoliths has shown that olive rockfish live at least 25 yr. Females grow larger, and, beginning at maturation, tend to be longer at a given age. The maximum reported length of olive rockfish is 24 inches. This is one of the fastest-growing nearshore rockfishes. Based on whole otoliths, a 10-in. TL fish is approximately 2-3 yr old, a 15-in. TL fish is approximately 10 yr old, and an 18-in. TL fish is approximately 10 yr old.
Reproduction, Fecundity and Seasonality
Throughout California, males mature at a somewhat smaller size and a slightly greater age than females, however the difference is not large. First maturity for males ranges from 10.6 (no age given) to 12.6 in. (4 yr). First maturity for females ranges from 11.2 (no age given ) to 12.6 in. (4 yr). Fifty percent maturity for males occurs between 12.6 and 13.0 in. (both 5 yr), while 50% maturity for females occurs between 13.4 (4 yr) and 13.8 in. (5 yr).
Mating occurs in the fall and females release larvae once a year in the winter from December through March, peaking in January. Larvae are planktonic for 3 to 6 months, then from April to September, young-of-the-year olive rockfish, around 1.2 to 1.6 inches long, settle out of the plankton.
Juvenile olives feed on crustaceans, juvenile fishes, polychaetes, octopi and squid. Juvenile olives become more active at night, but it is not clear whether adult olives are nocturnal: they do feed commonly on octopi, which are more available at night. Adult olive rockfish feed on fish (especially juvenile rockfishes), small crustaceans, polychaetes, cephalopods and tunicates. Adults are preyed upon by sharks, dolphins, and pinnipeds such as seals and sea lions. Juveniles fall prey to other rockfishes, lingcod, cabezon, salmon, albacore, birds, and porpoise.
Olive rockfish are known to compete with the kelp bass (Paralabrax clathratus) for food and shelter in southern and central California where their ranges overlap. Though olive rockfish have been associated with surfperches and bocaccio, and are frequently observed among schooling blue rockfish, no information on competition among them was found.
As with all rockfishes, the larval stage of olive rockfish is planktonic. When young-of-the-year olive rockfish settle out of the plankton they are most commonly found in and around kelp beds, oil platforms, surfgrass and other structures at depths as shallow as 10 ft. Sub-adult and adult olives live over high-relief reefs, as well as around the midwaters of oil platforms. In shallow waters, they are found throughout the water column in and around kelp beds, and are known to rest on the bottom as well.
The movement patterns of olive rockfish may be limited by the presence or absence of kelp beds. It has been shown that the abundance of olive rockfish decreases as beds of Macrocystis are removed.
Status of Stocks
There has been no stock assessment of this species. However, there is clear evidence from sport fish catch records that olive rockfish have declined in abundance south of Point Conception.
Information on this page was originally presented in the Nearshore Fishery Management Plan (these profiles updated July, 2010).