Predation, feeding strategy and food daily ration in juvenile European hake

Predation, feeding strategy (FS) and food daily ration (DR) were analysed in juveniles of the European hakeMerluccius merlucciusduring a 24 h trawl survey carried out in the northwestern Mediterranean. Predatory activity, expressed as the stomach fullness index (FI) and prey digestion stage, was initiated in the early night and continued throughout the night, reaching maximum activity in the early morning. The feeding activity progressively decreased after this time, reaching a minimum before sunset, when a rest phase was observed. Changes in prey taxa during the 24 h cycle indicated that prey selection was time-of-day and predator-size dependent. Zooplankton crustaceans were mostly consumed during the night and in the early afternoon. The 2 main categories (euphausiids and mysids) comprising the zooplankton and hyperbenthos trophic resource of the hake, were consumed in a temporally shifted manner, such that the macrozooplankton (euphausiids) was consumed at night and the hyperbenthos (mysids) during the day. FS and length-distribution analysis indicated that early juveniles (9.3 ± 1.7 cm total length, TL) primarily fed on these resources in these periods. In contrast, advanced juveniles (12.0 ± 3.4 cm TL) preyed largely on decapod crustaceans and fishes and fed mostly during the day, exhibiting a more specialised FS. Differences in the DR were estimated using Exponential (Exp) and Square-root (Sq-r) models, the latter taking into account predator size. The Exp model yielded a mean consumption of 1.5% body wet weight (BWW) and the Sq-r model yielded mean values ranging between 4.09 and 5.09% BWW, with a difference between the 2 methods ranging from 63 to 70% larger for the latter method. Therefore, the application of the Sq-r model gives an alternative insight into the range of consumption in juvenile hakes.