Seasonal variation in the consumption of food by fish in the North Sea and implications for food web dynamics

Abstract

Previous North Sea food web studies are reviewed. These studies used estimates of primary production and fish energy requirements, then manipulated the energy flow pathway between the two to balance the budget. The resulting pathways largely ignored actual fish diets and consumption rates. In the present paper, North Sea biomass flow food webs are constructed for each quarter of the year from published estimates of fish abundance, diet and daily food consumption, and using long-term Continuous Plankton Recorder and North Sea benthos survey data. Estimates of daily production of each component of the web are derived from specific daily growth and gross growth efficiency measurements. The flow of biomass from secondary production to fish is sufficient to supply the food requirements of planktivorous pelagic fish and benthivorous demersal fish. Piscivorous pelagic fish obtain much of their food requirements from outside the North Sea. The food requirements of piscivorous demersal fish also do not appear to be adequately supplied from within the North Sea, but, in this case, immigration is not thought to provide the shortfall. The high predation pressure on demersal piscivores may explain why this group appears to be especially vulnerable to fishing. The supply of biomass from primary production to secondary producers appears to be sufficient without the need to postulate import into the North Sea. Indeed, the supply to the benthos is such that a detritivore trophic level can be inserted between organic settlement and production of macrobenthos

Predicting abundance–body size relationships in functional and taxonomic subsets of food webs

“…Greenstreet et al 1997). Thus, the results of the nitrogen stable isotope analyses show that trophic level tends to fall with increasing body size, resulting in potentially greater energy availability for individuals of larger body size.…”

Bottom-up control regulates fisheries production at the scale of eco-regions in European seas

“…This is typically the case in the coastal North Sea and might explain some the differences between the PP averages used in the present study and some values derived from field measurements as reviewed by Greenstreet et al (1997). The accuracy of the SeaWiFS chl a product is much better constrained for open ocean waters • The simplified model representation of phytoplankton physiology and its vertical distribution, which results in discrepancies when model outputs are directly compared with measurements of individual stations.…”

Variability in behaviour of four fish species attracted to baited underwater cameras in the North Sea

“…These activity patterns are most likely related to diel feeding migrations. Adult whiting are largely demersal, daytime foragers targeting piscivorous prey (Hislop et al, 1991;Bromley et al, 1997;Greenstreet et al, 1997) but also disperse and feed in the water column at night (Patterson, 1985;Mergardt & Temming, 1997;Pedersen, 2000;Onsrud et al, 2005). Variation in behaviour is most likely related to local environmental conditions and particular prey assemblages such as vertically migrating sand eels, the preferred prey of both haddock and whiting at certain times of the year (Temming et al, 2004).…”