Ocean v.s. Coast: A Comparison of Growth-Survival Mechanism in Larval and Juvenile Stages Between an Oceanic Species, Chub Mackerel Scomber Japonicus, and a Coastal Species, Black Rockfish Sebastes Cheni in the Western North Pacific

Although previous studies demonstrated positive and negative selection for fast-growing individuals in fish early life stages in many species, comparative studies on such growth-survival mechanism among multiple species from different habits and ecosystems have been limited. Here, we compared the magnitude of selection for fast-growing individuals between larval and juvenile chub mackerel Scomber japonicus (an oceanic species) and black rockfish Sebastes cheni (a coastal species). Juvenile mackerel was collected at the offshore zone in May (original population: OP) and June (survivors: SV) of 2009-2013, and rockfish was collected at a macroalgal bed in April (OP) and May (SV) of 2008-2010 in the western North Pacific. Back-calculated growth trajectory using otolith microstructure analysis was compared between OP and SV within each species. Mean growth rate during larval and juvenile stages of SV was 18-22% higher than that of OP in mackerel except for 2011, and 6-12% higher in rockfish. The selection for fast-growing individuals was milder in the rockfish, which inhabit vegetated habitats during early life stages, than in the mackerel, which swim in pelagic waters without predation refuge. We concluded that life history traits and habitat structures partly contribute to the formation of the species-specific pattern in growth-survival mechanism.