Total lipid energy as a proxy for total egg production by fish stocks

The indeterminate relationship between the total biomass of mature fish (sp awner biomass) and the number of offspring produced (recruitment) has puzzl ed population dynamicists(1) and impeded fisheries management(2). The relat ionship assumes that spawner biomass (in tonnes) is proportional to the tot al number of eggs produced (TEP) by the stock(3), an assumption under incre asing challenge(4-8). Most stocks require proxies for TEP because contempor ary and/or historical fecundity data are lacking. Here we show a positive a ssociation between recruitment and the liver weights of spawners in the Bar ents Sea cod stock which suggests that recruitment is constrained by the am ount of lipid energy stored in the liver. This stimulated our interest in e stimating total lipid energy (TLE; in kilojoules) for mature females in the stock. We examined the suitability of TLE as a proxy through correlation a nd simulation analyses. The results indicate that TLE is proportional to TE P and exhibits a similar response to varying food abundance. Replacing spaw ner biomass with more accurate measures of reproductive potential is essent ial to developing a rational basis for stock conservation(9). Correctly spe cifying the first-order maternal effect on TEP is a prerequisite to detecti ng environmental and ecological effects on recruitment(10).