The basis of food selection in some estuarine fishes. Eels, Anguilla anguilla (L.), whiting, Merlangius merlangus (L.), sprat, Sprattus sprattus (L.) and stickleback, Gasterosteus aculeatus L.

Abstract

The basis of food selection in some estuarine fishes. Eels, A nguikla anguilla (L. ) , whiting , Merlangius merlangus (L.), sprat, Sprattus sprattus (L.) and stickleback, Gmterssteus aculeatus L.The factors influencing the selection of food by eels, AnguiNa anguilla, whiting, Merlungius merlangus, sprat, Sprattus spraitus, and stickleback, Gasterosteus aculeatris have Seen investigated by analysing col!ections made in the Severn Estuary for 1 year. Non-migratory (yellow) eels measuring from 19.5-56.5 cm in length fed mainly on either the decapod Crangon vulgaris or on the mysid Ni?ornysis integer during the warmer months but ceased to feed in the winter. Whiting measuring between 2.5 and 15 cm fed almost exclusively on C. vulgaris, A' . integer and the sand goby, Pornatuschistus nzinutus. Sprats fed chiefly on eithcr the amphipod Gammarus salinus or N. integer. Sticklebacks seldom contained any food in their stomachs despite the presence of large quantities of suitable prey and the high level of hunting cfficicncy. Gammarus salinus, although normally abundant in the environment, was usually ingested in disproportionately small quantities by all fishes except sprats reflecting its concealment among floating weeds and a selection against small (less than 1 crn) organisms. Because of the limitations of size and thc unusually efficient escape reaction of larger animals, only young representatives of Crangun vulgaris were captured. The isopod Eurydice pulchra was rarely eaten by any of the fishes even though it was common in the environment. Burrowing polychaetes, mainly Nereis rldversicolor, were never utilized possibly due to the difficulty involved in removing these organisms from the substrate. Neongvsis integer was the most frequently consumed organism. Although the average length of prey ingested by the whitings increased with the size of fish, this was not the case for the other species. The proportion of non-feeding eels and the dry weight of stomach contents of this species depended on the temperature of the water but were not related to the availability of prey and tidal conditions whereas the fceding of whiting could not be related to any environmental paramter.

Exploitation of trophic resources by fish under stressful estuarine conditions

“…The present study therefore invalidates the common hypothesis that estuarine fish are generally opportunists (e.g. Moore & Moore 1976, Cabral & Ohmert 2001, Laffaille et al 2001, Baldoa & Drake 2002, Elliott & Hemingway 2002. Only a minority of the pelagic and demersal fish community in the Gironde estuary -characterized by the marine juveniles Engraulis encrasicolus and Dicentrarchus punctatus and by the resident species Pomatoschistus minutus -were found to feed on the predominant abundant prey which differed from month to month.…”

“…Despite the differences in taxa, geographical distribution and environmental conditions, similar feeding requirements have been observed in other estuarine and marine systems: the small pelagic fish Sprattus sprattus and Engraulis encrasicolus are zooplanktivores (e.g. Plounevez & Champalbert 1999, Maes & Ollevier 2002; demersal fish, represented by Argyrosomus regius, Dicentrarchus labrax, D. punctatus and Merlangius merlangus, consume hyperbenthos (Moore & Moore 1976, Ktari et al 1978, Cabral & Ohmert 2001, Laffaille et al 2001; and Pomatoschistus minutus and P. microps eat both mesozooplankton and hyperbenthic prey (Salgado et al 2004, Leitão et al 2006). This interspecific feeding variability could be linked to different body structures, i.e.…”

Prey selection based on predator/prey weight ratios for some northwest Atlantic fish

“…Size as a controlling factor in prey preference by fish is well documented for a number of marine and freshwater species (Levings, 1974;Moore and Moore, 1976;Ross, 1977;Helfman, 1978;Keast, 1978). Prey size preference is also central to the concept of optimal foraging which is based on the premise of a maximization of energy return to the predator for each prey encounter (Werner a n d Hall, 1974;Krebs and Davies, 1979).…”

Seasonal, annual and regional variations in ichthyofaunal composition in the inner Severn Estuary and inner Bristol Channel

“…Since estuaries are highly productive ecosystems (Schelske & Odum, 1970) and thereby facilitate the rapid growth of juvenile fish, it is relevant that the inshore shallows of the Oldbury region contain high densities of small crustaceans, which are an important food source for juvenile fish in the region (Moore & Moore, 1976;Moore et al, 1979;Henderson et al, 1992). The important role played by the shallows of the Severn Estuary as a nursery ground for certain marine species parallels the situation recorded in temperate estuaries elsewhere in the Northern Hemisphere and also in the Southern Hemisphere (e.g.…”