Atlantic mackerel (Scomber scombrus) recruitment fluctuations in relation to copepod production and juvenile growth

A previous study identified relationships linking variations in the physical environment to fluctuations in zooplankton biomass and Atlantic mackerel (Scomber scombrus) recruitment. Diets of mackerel larvae were compared among four years, one of these years producing an exceptional year-class (1982). Comparisons were standardized for larval length and time of day. Stomach fullness differed significantly among years, with highest values observed in 1982. Stomach content wet weights were significantly larger in 1982 than in 1987 and 1996. The mean weight of Calanus finmarchicus nauplii prey in the diet was also significantly greater in 1982 than in 1985, 1987, or 1996. Female C. finmarchicus were more abundant and more widely distributed in the southern Gulf of St. Lawrence in 1982 compared with 1985, 1987, and 1990. These findings are consistent with the hypothesis of a link between production of copepod nauplii, feeding of mackerel larvae, and recruitment success. However, mackerel size at the end of the first year, as measured on otoliths, varied significantly between years and was smallest in 1982. We propose hypotheses to account for the coupling between high larval food abundance, small juvenile growth, and strong cohorts.