1. Institute of Marine Research, PO Box 1870 Nordnes, N-5817 Bergen, Norway
2. Polar Research Institute of Marine Fisheries and Oceanography, 6 Knipovich Street, Murmansk, 183763, Russia
3. Ministère des Pêches et des Océans, Institut Maurice-Lamontagne, C.P. 1000, Mont-Joli, G5H 3Z4, Canada

Correspondence to: C. Tara Marshall¹ Correspondence and requests for materials should be addressed to C.T.M. (e-mail: Email: tara@imr.no).

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 challenge^{4, 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.