Northern Benguela Merluccius paradoxus Annual Growth From Otolith Chronologies Used for Age Verification and as Indicators of Fisheries-Induced and Environmental Changes

In this study we develop a 32-year (1982–2013) otolith biochronology of the commercially important deepwater hake Merluccius paradoxus in the northern Benguela, Namibia. Mean annual growth (mm) calculated from 140 thin-sectioned M. paradoxus otoliths were compared with change in mean length at age 3 to age 4 determined from Namibian whole-otolith-read age-length keys (ALKs). Annual growth rates calculated from the two methods (overlapping 2000–2013) were strongly positively correlated (ρ=0.730, n=14, p300 m bottom depth, are thus strongly influenced by fisheries. As an upper-level demersal predator, this species integrates signals throughout the food web to provide a unique “view from the top” of long-term changes in the northern Benguela upwelling system. These results provide background ranges of growth variability and context for what will likely be negative impacts of predicted decreases in future upwelling.