Spatial variability in zooplankton and feedingof larval Atlantic mackerel (Scomber scombrus) in the southern Gul fof St. Lawrence

No abstracts are to be cited without prior reference to the author.

Availability of adequate zooplankton prey during the larval stage is a key factor for the emergence of a strong year class. There are inconsistencies in the literature on the importance of various zooplankton prey taxa for determining Atlantic mackerel recruitment in the southern Gulf of St. Lawrence. Previous studies identified the copepod Calanus finmarchicus as the most important prey influencing recruitment of Atlantic mackerel, whereas a recent study pointed to the importance of the copepod Pseudocalanus spp. The aim of this research was to examine the influence of various assemblages of copepod preys on the feeding of larval Atlantic mackerel. Fish larvae and their zooplankton prey were sampled over a grid of 65 stations covering the entire southern Gulf of St. Lawrence in June 2008 and 2010. We pooled stations in four groups based on zooplankton species assemblages. One assemblage was dominated by the copepods Oithona spp. and Temora longicornis and the three others were dominated by different proportions of Oithona spp. and Pseudocalanus spp. Feeding selectivity of mackerel larvae was measured by comparing zooplankton prey in their gut content with zooplankton found in their environment. Surprisingly, the diet in the 3.5–5.4 mm and the >5.4 mm size class was dominated by Oithona spp. and T. longicornis. Preliminary results indicated a positive selection for Oithona spp. and T. longicornis. These results about the preferred prey of Atlantic mackerel larvae will be useful to adjust predictive models of recruitment based on copepod production for this commercial fish.