Fluctuations in year-class size of striped bass (Morone saxatilis) are believed related to early-lifestage mortality. Factors associated with food and feeding of larvae were studied in the laboratory as they relate to mortality, point of no return, development, and energetics. Mortality of feeding larvae was directly related to density of Artemia salina nauplii. Highest mortality coincided with total oil globule absorption. Starved larvae lived an average 31 days after fertilization and did not display a well-defined point of no return. Growth and differentiation directly correlated with food density. Starvation affected the rate of ossification and altered cells and tissues as early as 7 days after hatching. Most of the endogenous energy of newly fertilized eggs is in oil. The rate of oil utilization was inversely related to food density. Daily food rations were estimated after ingestion and digestion rates were determined, and increased with larva size, age, and prey density.Between 1879 and 1882, 432 juvenile striped bass (Morone saxatilis) from the Navesink River, New Jersey, were released into the San Francisco Bay-Delta estuary. The transplant was so successful that, within 10 years, the commercial fishery landed 554 t (Skinner 1962). In less than 100 years, the Pacific range of striped bass has expanded south to 30 km below the United States-Mexico border and north to Barkley Sound, British Columbia (Miller and Lea 1972). Over the intervening years, sport and commercial catch records have indicated considerable fluctuations in the Pacific striped bass population (Smith and Kato 1979), and present estimates place the population at 33 to 40% of its peak 1960 estimate of 3.0 to 4.5 x 10 • fish. Recent field data indicate that mortality during the first 60 days after hatching determines the size of the adult population. Further, abundance of young-of-the-year juveniles is directly related to river outflows and diversion volumes in the Sacramento-San Joaquin River Delta (Chadwick et al. 1977). However, aside from direct export of eggs and larvae out of the estuary via water diversions, the actual causes of mortality remain undetermined. As part of a cooperative research program involving the

SynopsisField and laboratory studies were conducted for 3 years on the yellowtail rockfish, Sebastes flavidus, from Cordell Bank, California, in order to characterize the reproduction of this species whose northern stocks have declined. Research findings included reversal of the sex ratios and male-female ages and sizes at age throughout the annual cycle, heavier and longer females at age than males after sexual maturation, maturation of females at 6 and males at 8 years, long reproductive lifespans, distinct male and female gonadosomatic index patterns over the annual cycle, age-and size-specific fecundity, no difference between potential and realized fecundity and the seasonal changes associated with gonadogenesis. The reproductive profile of the Cordell Bank yellowtail rockfish provided a base for comparison with northern populations that appeared to differ, especially in age and size.

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Fecundities of the commercially important yellowtail rockfish Sebastes flavidus were compared to determine interannual variability and geographic variation, which will assist in stock assessment, characterization, and management. Gravimetrically estimated fecundities were compared in 1985–1991 between California, the southern extent of the speciesˈ distribution, and coastal waters of Washington, near the center of the speciesˈ abundance, where yellowtail rockfish are most heavily fished. California yellowtail rockfish were older, smaller in weight and length, and had smaller mesenteric fat deposits and more extensive disease and parasite pathologies than Washington fish. Egg production of this comparatively fecund viviparous fish increased linearly and sigmoidally with body weight and length, and asymptotically with age. Significant interannual differences were found in fecundities of young fish (age 14) or in young or old Washington fish. Washington yellowtail rockfish had higher group fecundities because they were larger at age. Rate‐specific fecundities were significantly higher in young Washington fish. Predictive models of fecundity were highly correlated for young yellowtail rockfish, less so for old fish. Although fecundity of young fish depended on weight, length, and age, that of old fish was age‐independent. Our findings show age‐dependent interannual and geographic differences in reproductive effort, which suggest population‐specific reproductive life histories.

Total mean gestation period of all female yellowtail rockfish Sebastes flavidus, from fertilization to parturition, was 29·2 days. Hatching occurred 23 days after fertilization, followed by 6 days of larval incubation. Eggs varied in dry mass and energy content with lipid concentrations contributing the greatest amount of energy per egg. The endogenous energy of the yolk and oil globule declined throughout gestation resulting in limited yolk and oil reserves at parturition.