Daily ration and feeding activity of juvenile hake in the central Mediterranean Sea

Abstract

We investigated daily ration, feeding rhythms and gastric evacuation rates of juvenile (<16cm total length) European hake Merluccius merluccius, using stomach samples collected during four 24-hour trawl surveys carried out in 2001-2002 on the continental shelf-break (from 120 m to 160 m in depth) off the western coast of central Italy (central Mediterranean Sea). In each survey 8 hauls Of 30 minutes were performed every three hours throughout the 24-hour period to cover the entire diel cycle. Diet of juvenile hake was mostly composed of the euphausiid Nyctiphanes couchii, showing a peak in stomach contents during early morning followed by a daytime decrease. Fullness index (%FI) was generally higher during sunrise when migratory activity ceased and juvenile hake return to the bottom after feeding. Concerning the hake abundance the highest density value was obtained in May during the recruitment period. Two independent daily ration estimates were produced. First, an empirical attempt to estimate the daily amount of food consumed was obtained by back-calculating the fresh weight of euphausiid prey ingested by juvenile hake. Estimated values ranged from 4.96-5.89% body wet weight (%BW). Second, the daily ration was computed applying the exponential gastric evacuation models proposed by Elliot & Persson (1978) and Eggers (1979). Daily ration values obtained using these consumption models produced a considerable (15 - 20%) underestimation of consumption rate for juvenile hake

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

“…The consumption estimate obtained using the Exp model falls into the range of food consumption (1.01 to 5.51% BWW) calculated for the same species by Cartes et al (2004) from 3 different 8 h cycles, but it is lower than the value given by Carpentieri et al (2008), probably because of the different daily sampling periods considered. In fact, Carpentieri et al (2008) pointed out that no reliable data on stomach fullness were available in their dataset for the night. The lack of samples for the night period and, in particular, for the first part of the night, could have biased their food consumption calculation, resulting in an overestimation, because a low predatory activity phase was observed in this period.…”

“…Previous studies on feeding patterns of hake showed different feeding rhythms; maximum predatory activity was recorded either at night (Carpentieri et al 2008), during the day (Cartes et al 2004, Bozzano et al 2005 or in both periods (Cartes et al 2009). These discrepancies might be due to the different size ranges of individuals analysed in each study.…”

“…Because the number of stomachs collected in each haul varied widely, normalisation was applied by dividing the number of prey belonging to the main taxa by the number of stomachs analysed in each haul. Additionally, crustacean taxa were split into decapods and zooplankton and hyperbenthos (Euphausiacea and Mysidacea) since the latter group is recognised as one of the most important prey taxa for juvenile hake in the Mediterranean (Orsi-Relini et al 1997, Ferraton et al 2007, Carpentieri et al 2008, Cartes et al 2009). Finally, the presence and variation in abundance of zooplankton and hyperbenthos crustaceans in the stomach contents were analysed in terms of percent of frequency of occurrence (% FO) and digestion stage over time.…”

“…for European hake; Cartes et al 2004, Carpentieri et al 2008). The consumption estimate obtained using the Exp model falls into the range of food consumption (1.01 to 5.51% BWW) calculated for the same species by Cartes et al (2004) from 3 different 8 h cycles, but it is lower than the value given by Carpentieri et al (2008), probably because of the different daily sampling periods considered. In fact, Carpentieri et al (2008) pointed out that no reliable data on stomach fullness were available in their dataset for the night.…”

“…The European hake Merluccius merluccius (L. 1758) has great ecological and economic importance in the Mediterranean Sea and the North Atlantic Ocean (Alheit & Pitcher 1995). Its diet has been widely studied in both Atlantic (González et al 1985, Guichet 1995, Velasco & Olaso 1998 and Mediterranean waters (Froglia 1973, Bozzano et al 1997, Ferraton et al 2007, and food consumption has been analysed by Velasco & Olaso (2000), Cartes et al (2004) and Carpentieri et al (2008). However, a complete study of the DR in this species during a 24 h cycle is still lacking, probably because of the difficulties in collecting enough specimens during a daily cycle, where part of the population performs spatial and temporal migrations (Bozzano et al 2005, Carpentieri et al 2006, Cartes et al 2009).…”