Abstract
The indeterminate relationship between the total biomass of mature fish (spawner biomass) and the number of offspring produced (recruitment) has puzzled population dynamicists1 and impeded fisheries management2. The relationship assumes that spawner biomass (in tonnes) is proportional to the total number of eggs produced (TEP) by the stock3, an assumption under increasing challenge4,5,6,7,8. Most stocks require proxies for TEP because contemporary and/or historical fecundity data are lacking. Here we show a positive association between recruitment and the liver weights of spawners in the Barents Sea cod stock which suggests that recruitment is constrained by the amount of lipid energy stored in the liver. This stimulated our interest in estimating total lipid energy (TLE; in kilojoules) for mature females in the stock. We examined the suitability of TLE as a proxy through correlation and simulation analyses. The results indicate that TLE is proportional to TEP and exhibits a similar response to varying food abundance. Replacing spawner biomass with more accurate measures of reproductive potential is essential to developing a rational basis for stock conservation9. Correctly specifying the first-order maternal effect on TEP is a prerequisite to detecting environmental and ecological effects on recruitment10.
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