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Research Document 1997/71

Assessment of the Atlantic mackerel (Scomber scombrus L.) biomass for 1996 by the Total Eggs Production Method

By F. Grégoire, J. Lambert, C. Lévesque, M.-F. Beaulieu

Abstract

The 1996 survey to assess the Atlantic mackerel biomass began three days later than planned, on June 18. On the first set, surface water temperatures were noted to be higher than during the initial sets of previous surveys. Furthermore, eggs at later development stages and mackerel larvae were more numerous. Daily egg production for the two sets was evaluated at 0.6604 x 1013 and 0.6129 x 1013 eggs, with corresponding spawning biomass values of 259,842 t and 241,318 t. The biomass values fell to 211,023 t and 206,566 t when the egg densities at each station were corrected for the oversampling that occurs at the end of tows. When these corrected densities were applied in the geostatistical approach, daily production values of 0.6068 x 1013 and 0.6366 x 1013 eggs were obtained for the sets, yielding biomass values of 238,897 t and 250,628 t. Using this approach, it was also determined that there is a close relationship between egg density and water temperature. This relationship can be used to improve abundance estimates in the future. Because the timing of the survey and spawning were not well synchronized and owing to the method used to derive the seasonal egg production curve, the abundance estimate for 1996 should be considered a minimal value.

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