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

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Abstract
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%.