Sex-specific food intake in whiting Merlangius merlangus

Seasonal and ontogenetic variation of whiting diet in the Eastern English Channel and the Southern North Sea

An accurate description of trophic interactions is crucial to understand ecosystem functioning and sustainably manage marine ecosystems exploitation. Carbon and nitrogen stable isotopes were coupled with stomach content analyses to investigate whiting (Merlangius merlangus, Linnaeus, 1758) feeding behavior in the Eastern English Channel and Southern North Sea. Whiting juveniles and adults were sampled in autumn and winter to investigate both ontogenetic and seasonal changes. In addition, queen scallops (Aequipecten opercularis) samples were collected along with fish to be used as isotopic benthic baseline. Results indicated an ontogenetic diet change from crustaceans to fish and cephalopods. In autumn, δ¹⁵N values generally increased with fish size while in winter, a decrease of δ¹⁵N values with fish size was observed, as a potential result of spatial variation in baseline δ¹⁵N values. In winter, a nutrient-poor period, an increase in feeding intensity was observed, especially on the copepod Temora longicornis. This study provides further insights into whiting trophic ecology in relation to ontogenetic and seasonal variations, and it confirms the importance of combining several trophic analysis methods to understand ecosystem functioning.

Growth and food consumption of whiting Merlangius merlangus

In the western Baltic Sea (WBS), whiting Merlangius merlangus is the main piscivorous fish together with cod Gadus morhua. In the present study, we investigate the growth and food consumption rates of WBS M. merlangus and compare the growth rates of males and females with those of M. merlangus in the North Sea (NS). Food consumption rates are estimated directly from sampled stomach contents in the WBS using a gastric evacuation rate model and indirectly by using a static energy-budget model together with the growth rates. The results indicate that male and female M. merlangus in the WBS have similar feeding and growth strategies, while in the NS M. merlangus show more pronounced differences in food consumption and growth dynamics between the sexes. Female WBS M. merlangus grow significantly slower than their conspecifics in the NS, but there is no significant difference for males. Sexual size dimorphism is seen in both areas, but for M. merlangus in the WBS the difference is less pronounced. Food consumption rates in the WBS differ between seasons, with the lowest food intake in the first 2 quarters of the year and the highest in the 3rd quarter. No differences in consumption rates were seen between males and females, which could be related to the more similar growth pattern seen for M. merlangus in the WBS.

The diet of whiting Merlangius merlangus in the western Baltic Sea

The diet of whiting Merlangius merlangus in the western Baltic Sea was investigated and compared to the diet in the southern North Sea. Clupeids were important prey in both areas, but especially in the western Baltic Sea where they constituted up to 90% of the diet of larger individuals. Gobies, brown shrimps and polychaetes were the main prey of juveniles in the western Baltic Sea, while a wider range of species were consumed in the North Sea. The shift to piscivory occurred at smaller sizes in the western Baltic Sea and the fish prey consumed was proportionately larger than in the southern North Sea. Estimates of prey abundance and food intake of M. merlangus are required to evaluate its predatory significance in the western Baltic Sea, but its diet suggests that it could be just as significant a fish predator here as in the southern North Sea.