Patience and luck would be my guess. I would say a throw net, but that could get you in trouble and cause serious harm to the fish. If it were me I would make a couple walks to see if I can find out their habits and where they might be at certain times. When I fish or hunt I look for travel paths and predator ambush points so the same principle would apply in this instance. I would also look at a larger fine mesh net. The bait nets for fishing work very well.
John
"Critics are men who watch a battle from a high place and then come down and shoot the survivors." Ernest Hemingway