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Letters to Nature

Nature 402, 288-290 (18 November 1999) | doi:10.1038/46272; Received 15 July 1999; Accepted 15 September 1999

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

C. Tara Marshall1, Nathalia A. Yaragina2, Yvan Lambert3 & Olav S. Kjesbu1

  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).

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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.