Atractoscion nobilis
Seatrout
(Also: White seabass; White weakfish)

White sea bass can be found along the Pacific coastline, from Alaska to Baja California and in the Gulf of California. Larval and juvenile white seabass are often found in Sebastian Vizcaino Bay and San Juanico Bay, Baja California. (Donohoe, 1997)

Atractoscion nobilis inhabits brackish waters and usually prefers demersal areas. Rocky reefs and soft bottomed habitats are ideal. Juveniles are often found in shallow water along the coast, just beyond the surf zone where they preys upon mysids and drifting macrophytes. Juveniles can also be found in estuaries and coastal bays, which serve as nursery stations until individuals are large enough to survive further offshore. Maximum depth for A. nobilis is about 122 m. (Donohoe, 1997)

White seabass are moderately elongate and silver. They have two dorsal fins; the anterior dorsal fin contains 9 to 11 spines, and the posterior dorsal fin contains one spine with several soft rays extending behind it. They also have pelvic fins on the thorax, which are slightly posterior to the pectoral fins, a general characteristic of the family Sciaenidae. The lower jaw is marginally longer than the upper jaw, and the teeth are relatively small. The lateral line is slightly curved and extends from the operculum past the caudal peduncle to the edge of the indented tail fin. They also have a ridge that runs along their underbelly, a characteristic unique to this species. White seabass under 61 cm in length are considered reproductively immature. Young A. nobilis have dark yellow fins, and are predominantly silver, with 3 to 6 dark vertical bars on their sides. Adults are countershaded, with a ventral silvery color and a bluish-gray or copper dorsal color. Adults can grow to be 152 cm long and can weigh up to 41 kg. Sexual dimorphism has not been reported in this species. ("A Field Guide to Pacific Coast Fishes : North America", 1983; "California Marine Food and Game Fishes", 1971)

White seabass have the largest eggs of the six of Sciaenidae species found throughout the coastal waters of southern California. Fertilized eggs (1.24 to 1.32 mm in diameter) are most commonly found off the coast of Baja California, near Sebastian Viscaino Bay and San Juanico Bay. After hatching, larvae are about 2.8 mm in length. Juvenile fry have black bands which disappear at sexual maturity around 4 years of age. Maximum length of an adult white seabass is 1.5 m, with a maximum weight of 45 kg. ("California's Living Marine Resources: A Status Report", 2001; Ambrose, et al., 1983; Steele, et al., 2007; Zimmerman and Lowery, 1999)

White seabass are promiscuous. Males and females spawn multiple times with different partners. (Drawbridge and Aalbers, 2008)

White seabass can spawn up to 5 or 6 times a year. Spawning generally occurs between April and August, when water temperatures are 18 degrees Celsius. Generally, white seabass reach sexual maturity between 3.5 and 4.5 years of age. Females are mature by 4 years of age and nearly 61 centimeters long, and males become sexually mature by 3 years and 51 centimeters long. Females can produce over 1.5 million eggs per spawning event. As a female becomes ready to spawn, she develops distinct black lateral bars and decreases her swim rate. When identified as a reproductive female, she is pursued by multiple males, which compete for prime spawning positions. After the eggs are fertilized, adults do not remain to protect them. Eggs develop while suspended in the water column until several months later, when they develop into free-swimming fry. ("California's Living Marine Resources: A Status Report", 2001)

As White seabass are broadcast spawners, parental care is nonexistent. Fertilized eggs develop while suspended in the water column. ("California's Living Marine Resources: A Status Report", 2001)

As small fry (between 0.6 and 5.7 cm long), white seabass inhabit coastal waters ranging from 3.6 to 9 m in depth. At 1 to 3 years of age, they seek out the calm waters of various bays, where they find refuge in eel grass beds. Lifespan in the wild is unknown, however, data recovered from tagged and recaptured individuals suggests they can live to be greater than 12 years old. ("California's Living Marine Resources: A Status Report", 2001; "White Seabass Fishery Management Plan", 2002)

There is little data on the general behavior of white seabass in the wild. Captive-bred individuals that have been tagged at hatcheries, have been recaptured at locations up to 85 nautical miles away. Other evidence from tagged specimens suggest that these fish tend to migrate northward along the coast as ocean temperatures rise during summer, or as warmer extend north during El Niño events. ("White Seabass Fishery Management Plan", 2002)

Based on genetic studies, there appears to be 3 distinct populations: one in coastal southern California, one in coastal northern California, and one in the Sea of Cortez. Given that individuals can move at least 85 nautical miles within these areas, it is unlikely that home ranges are maintained. ("White Seabass Fishery Management Plan", 2002)

Aside from adaptations common to most bony fish species, little is known about how Atractoscion nobilis communicates with conspecifics and perceives its local environment. However, all members of Sciaenidae produce drumming sounds, a characteristic unique to this family. These low-frequency sounds are created by muscles that vibrate the swim bladder, making a sound like a drum roll. Males often make drumming calls just prior to spawning. ("White Seabass Fishery Management Plan", 2002; Rountree, 2008)

Atractoscion nobilis feeds on northern anchovy, market squid, Pacific sardines, blacksmith, silversides, and pelagic red crab. Larger A. nobilis also feed on Pacific mackerel, and juveniles feed almost exclusively on mysid shrimp. ("Ken Schultz’s Field Guide to Saltwater Fish", 2003; "Ken Schultz’s Field Guide to Saltwater Fish", 2003; "Shorefishes of the Tropical Eastern Pacific", 2008)

Although predation on juveniles likely has a major impact on the distribution and abundance of white seabass, juvenile specific predators are currently unknown. However, it’s likely that any carnivorous fish will prey on them if they have the opportunity. Although adults have few predators within their ecosystem, great white sharks and California sea lions have been known to attack white seabass trapped in gill nets. Because it is a prized food fish, it has long been the target of commercial and sport fishers. Thus, humans are the most significant predators of white seabass. The coloration of white seabass may help help reduce risk of predation. ("California Marine Food and Game Fishes", 1971; "The Ecology of Marine Fishes: California and Adjacent Waters", 2006; "White Seabass Fishery Management Plan", 2002; "White seabass (Atractoscion nobilis) in California–Mexico Waters: Status of the Fishery", 1983)

White seabass are secondary and tertiary consumers of smaller fish within rocky bottom areas and giant kelp forests. It is not known whether they directly compete with other predatory fishes within these ecosystems. White seabass are host to a number of different endo- and ectoparasite. Studies have found at least three species of copepod (Neobrachiella gracilis, Lepeophtheirus thompsoni, and Lepeophtheirus abdominis) throughout the exterior body and inside the mouth. Endoparasites known to use white seabass as a host include three different species of cestodes (Lacistorhyncus tenuis, Callitetrarhynchus gracilis, and Grillotia smarisgora), which were found within the internal organs and the mesentery, and two types of protozoans (Kudoa clupeidae and Ceratomyxa venusta), found within muscle tissue and gall bladder. Other parasites known to occupy the tissues of white seabass at some point throughout their life cycle include flatworms and roundworms, most of which can be found in the intestines. White seabass rarely experience significant negative effects due to parasitic infestations. ("Ken Schultz’s Field Guide to Saltwater Fish", 2003; "White Seabass Fishery Management Plan", 2002; Limbaugh, 2010)

White seabass are an important commercial fish species, and are taken by commercial trawlers and sport fishermen. However, overfishing has led to a serious decline in the population, which is why white seabass hatcheries have been developed. The development of these hatcheries has helped to increase the population of white seabass and to create jobs. ("Hubbs-Seaworld Research Institute", 2008; Chao, et al., 2010)

There are no known negative economic impacts to humans.

White seabass are currently listed as a species of least concern on the IUCN's Red List of Threatened Species. Although their numbers are low when compared to historical abundance, population size has increased over the past 30 years due to conservation and management efforts, including stricter regulations on fishing limits and the development of hatcheries. However, a small subpopulation in the Gulf of California is suspected to be in serious decline due to overfishing. ("California Marine Food and Game Fishes", 1971; Chao, et al., 2010)

In the mid 1970's, Hubbs-Sea World Research Institute in Carlsbad, California was founded under contract of the California Department of Fish and Game and became operational in 1995. It serves as an important resource, working in tandem with the White seabass Management Plan, to raise White seabass from eggs spawned in captivity through the juvenile stage before fry are released into the ocean. Once the fertilized eggs hatch, larvae are held in a cone tank without food for 4 days. For the next 25 days, fish larvae are fed newly-hatched nauplius larvae of brine shrimp (Artemia salina) and are moved to a round tank after 18-20 days spent in the cone tank. When the fish are 40-50 days old, their diet is slowly changed to dry pellets, and the fish are moved into a series of 6 tanks to allow them to grow but also to keep the larger individuals separate from smaller ones, since white seabass are cannibalistic. When average size and weight reaches about 10cm and 10g, small tags are inserted into the fish's cheek. While being handled and tagged, fish are placed into an anesthetic bath. Each tagged fish is put into a tube with a metal detector to make sure the tag has been successfully inserted. After being tagged, the fish are moved from their indoor tanks to outdoor pens in bays and coastal lagoons, where they will be held and fed for a minimum of 90 days or until they reach 20cm in length. Animals are released shortly there after. ("Hubbs-Seaworld Research Institute", 2008; "White Seabass Release-Recapture Facts", 2008)

Money collected from the sale of fishing license stamps bought in California between Santa Barbara and the San Diego funds the Sea World-Hubbs Research Institute. The hatchery is capable of producing 350,000 juvenile white seabass annually. A person who returns the head of a legal-sized tagged White seabass to the California Department of Fish and Game is entered in a raffle to win $500.00. Since hatcheries became operational, over 1800 fish have been recaptured, of which 156 were legal size (over 71 cm). The oldest tagged fish was released in 1994 and recaptured in 2007. ("Hubbs-Seaworld Research Institute", 2008; "White Seabass Release-Recapture Facts", 2008)