Herons and fish farming in the Huleh Valley, Israel: Conflict or mutual benefit?

The impact of populations of the Black-crowned Night-Heron, (Nycticorax nycticorax) and Little Egret (Egretta garzetta), on freshwater commercial fish farms (carp, Cyprinus carpio and tilapia, Sarotherodon spp.) was assessed in the Huleh Valley, Israel. Energy requirement calculations were based on heron population counts, feeding, breeding and survival parameters, daily energy requirement and fish farming management data. The heron populations in the study require 17.2 x 10(6) fry, while ponds were populated during the year with 9.8 x 10(6) fish fry Moreover, fish of the size found in herons' stomachs throughout the year are available among commercial fish only for a period of 6-8 weeks, twice yearly. It is assumed that the main source of tilapia fry in both herons' diet is from uncontrolled proliferation in the ponds. Thr presence of the herons contributes to the improvement of commercial fish gl owing conditions by: (a) reducing density of uncontrolled fish fry; (b) eliminating unhealthy fish; (c) eliminating stocked fish fly predators; and (d) indicating undesired conditions in ponds.