Research Document 1997/84
Évaluation de la Méthode de la Réduction Journalière de la Fécondité pour estimer la biomasse du maquereau bleu (Scomber scombrus L.)
By F. Grégoire
Abstract
The "Daily Fecundity Reduction Method" was evaluated to determine whether this approach can be used to estimate the spawning biomass of the Gulf of St. Lawrence mackerel. One of the key advantages it offers is that the biomass is calculated from the estimate of daily egg production rather than estimate of total annual egg production. Hence, there is no need to use or make an assumption about the shape of the seasonal egg production curve. Furthermore, since the method is based on the reduction in fecundity that occurs during the spawning season, an underestimation will not result even if the egg survey does not coincide with spawning, as sometimes happens with the "Total or Annual Egg Production Method" which is currently in use. No major obstacles were encountered in using this method with mackerel. The spawning biomasses obtained for the two sets of the 1996 survey were 442,608 t and 554,063 t respectively. These values are higher than those obtained with the current method, which does not contain a correction for the fact that spawning was already well under way when the 1996 survey began. In view of the results, this method will be applied again during the next egg survey, planned for summer 1998. It may subsequently be adopted as the standard method for calculating the biomass of the Gulf of St. Lawrence mackerel.
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