Spatio-temporal variation in the diet of northern pike (Esox zucius) in a colonised area (Esla basin, NW Spain)

The stomach contents of 4,362 northern pike (Esox lucius) captured over six years in the Esla Basin (NW of Spain) were examined. The frequency of occurrence and the numeric percentage of each taxon-prey was calculated separately for each river and at monthly intervals. The spectrum of the northern pike diet in the Esla Basin was very broad. They consume prey of all groups of aquatic invertebrates and vertebrates available. They are generalist predators. The high diversity and uniformity values of their diet suggests little ,food selection. The similarity shown in diet composition of pike in the different stretches is very high. Howevet; diet in different stretches may differ due to the presence of accidental prey. The percentage of pike with empty stomachs in samples was highest before spawning (i.e. 84 % in February) but dropped to 12 % in Map when reproduction had ended. Monthly variations in the percentage of pike with an empty stomach were statistically significant.