Diet and condition of juvenile deep-water hake Merluccius paradoxus on the west coast of southern Africa

Abstract

The composition of the diet of juvenile deep-water hake Merluccius paradoxus is described and compared for three body-condition groups (below-average, average, and above-average). Diet was analysed using three metrics: occurrence, numeric and gravimetric. Juvenile hakes were caught in January and February of 2012 by means of 28 trawl deployments from the RV Dr Fridtjof Nansen between Orange Banks and Hondeklip Bay on the west coast of southern Africa at depths of 30-232 m. The 300 individuals analysed were a representative sample of all juveniles caught (3 114 fish), ranging in length from 52 to 205 mm (average length 107 mm). Their diet consisted of the euphausiid Euphausia lucens, the hyperiid amphipod Themisto gaudichaudii, the stomatopod Pterygosquilla armata capensis, and mesopelagic fishes Maurolicus muelleri and Lampanyctodes hectoris. The only significant difference in diet between the body-condition groups was for euphausiids and hyperiid amphipods in the numeric metric. A new method of assessing fish condition using otolith weight was tested. Because of the large variability in the data and small sample size, this method could not be applied effectively in this study. However, otolith weight has potential as a new fish condition metric when the variability can be lowered.