Fecundity and its variability in orange roughy: Effects of population density, condition, egg size, and senescence

Fecundity of orange roughy in 1987-1989 adjusted for standard length (S.L.) varied significantly between New South Wales (42 787 eggs female(-1)) South Australia (35 339 eggs female(-1)) and east Tasmania (31 085 eggs female (-1)). Only 10-17% of the variability in fecundity of eastern Tasmania orange roughy was explained by S.L. in any year from 1987-1992. However, liver condition and age of the fish, in combination with S.L., explained 27% of the variation in fecundity. Fecundity declined in fish over 60 years old. It was also significantly correlated with lipid levels in the ovary, in particular, with triacylglycerol as a proportion of the total lipid fraction. Significant interannual changes in fecundity appeared to be related to the impact of fishing. From 1987-1992, the orange roughy stock off east Tasmania was reduced by 50% by the fishery, and mean fecundity increased 20% over that period. This compensatory increase in individual fecundity, combined with an apparent increase in the proportion of females spawning annually from 54 to 71%, limited the decline in the population's egg production over this period to approximately 15%. (C) 1995 The Fisheries Society of the British Isles