Spatial variability in zooplankton and feeding of larval Atlantic mackerel (Scomber scombrus) in the southern Gulf of St. Lawrence

• Published in: Journal of Plankton Research
• Main Authors: Paradis, Vanessa, Sirois, Pascal, Castonguay, Martin, Plourde, Stéphane
• Format: Text
• Language: English
• Published: Oxford University Press 2012
• Subjects: Article; Calanus finmarchicus; Copepods
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/fbs063v1; https://doi.org/10.1093/plankt/fbs063

The 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 organism influencing Atlantic mackerel recruitment, while 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 prey 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 into 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 contents to zooplankton found in their environment. The diets of the 3.5–5.4 mm and the >5.4 mm size classes were dominated by Oithona spp. nauplii and T. longicornis nauplii and copepodites. These prey were generally positively selected by the larvae, unlike Pseudocalanus spp. This is the first study to demonstrate strong predation by mackerel larvae on Oithona spp. nauplii in the Gulf of St Lawrence. We suggest that an exceptional mackerel year class will be produced by a very high availability of large copepod prey throughout the southern Gulf of St Lawrence rather than a high availability of small copepod prey. These results on the preferred prey of Atlantic mackerel larvae will be useful in adjusting predictive models of recruitment based on copepod production for this commercial fish.