Early growth and recruitment in Atlantic mackerel Scomber scombrus: Discriminating the effects of fast growth and selection for fast growth

Abstract

We tested the hypothesis that strong recruitment in Atlantic mackerel Scomber scombrus occurs only in years when larval growth is fast and predation pressure - as measured by selection for fast growth - is weak. Four annual cohorts of larvae (1997, 1998, 1999 & 2000) were sampled on the Magdalen Shallows, southern Gulf of St. Lawrence, and 1 yr old mackerel juveniles were sampled the year after in the mackerel fishery of the southern Gulf. The early larval growth trajectories of both larvae and juveniles were back-calculated from the analysis of the sagittal otolith. Interannual differences in growth measured in the larvae persisted in the juveniles. The growth of larvae was significantly higher in 1999, an exceptional year class, than in the 3 other weak year classes. Surviving juveniles of the strong 1999 and the weak 1997 year classes grew equally fast during the first 40 d of larval life, but selection for fast growth was mild in 1999 and severe in 1997. We conclude that fast early growth measured in 1 yr old juveniles reflected fast growth of the entire larval population in 1999, and strong selective mortality against slow-growing larvae in 1997. Early growth was slow in larvae and juveniles of the weak 1998 (mild selection) and 2000 (no selection) year classes. Consistent with the hypothesis, the combination of fast growth and weak selection for fast growth unique to the 1999 cohort resulted in exceptional recruitment. © Inter-Research 2007.