Research Document - 2007/073

Results of the Atlantic mackerel (Scomber scombrus L.) egg survey conducted in the southern Gulf of St. Lawrence in 2006

By Grégoire, F., C. Lévesque, J.-L. Beaulieu, C. Méthot, and M.-H. Gendron

Abstract

A survey for assessing the spawning biomass of Atlantic mackerel (Scomber scombrus L.) by egg sampling was conducted in the southern Gulf of St. Lawrence between June 28th and July 8th, 2006. Some very low egg abundance, less than 10 eggs/m², was recorded at nearly 75% of the sampled stations. The highest abundance was recorded at stations located west of the Magdalen Islands. These stations were associated to water temperatures (0-10 m layer) varying between 9.3 °C and 12.3 °C. The mean egg production for the entire sampled area was calculated at 7.4 eggs/m², and total production at 5.12 x 10¹¹ eggs. A spawning biomass of 54,133 t was associated with this egg production, which represented the lowest recorded value since 1979. The 2006 survey was conducted towards the end of the spawning season as indicated by the daily egg production curve, the high water temperatures, between 9.3 °C and 16.7 °C, and the presence of larvae at just about every station. When considering these results, the assessed biomass for 2006 is associated to the portion of the stock that reproduced at the very end of the spawning season rather than the entire stock. In order to improve the mackerel abundance assessment, it is suggested that the survey be conducted at more appropriate dates. The 2006 survey could not be conducted earlier due to a conflict in time management for vessels. It is also suggested that the survey cover the Scotian Shelf due to the recent changes in mackerel migration routes.

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