The Three Spined Stickleback has made itself at home all along every Estuary system in Southern Ireland, it can go from fresh to salt water on an hourly basis, but favoring the Brackish water with plenty of cover to conceal itself in. They will “roll” with any other small fish in the system, eg young pollack, etc, but most commonly young mullet….
They are on the menu for many Estuary predators eg, Herons, Egrets, Kingfishers, as well as our target, Sea-Trout. Salmo Trutta has been the nemesis of the Stickle in fresh, + salt water for Millennia, going way back to the Ice Retreat, check out the Sticklebacks interesting history here Ecology And Evolution . Stickleback’s, and other bait fish will hang around very certain locations along Estuary systems, incoming “Salty’s” on the flood tide seek out this “Buffet”, giving the angler a brief window to hook one.
Based on the stomach contents of the trout I’ve examined way back when you could keep them legally back in the 90’s. Were, out of the 72 Sea-Trout examined, 33 were empty, 38 had fish in the order of Sandeel, Sprat, Mullet, Stickleback, only 1 had a Sand Shrimp. Never had much faith in shrimp flies for “Salty’s” after that…….