Some of the world’s most famous conservationists have been hunters. Teddy Roosevelt, John James Audubon, and Ernest Hemingway each have the somewhat dubious distinction of saving animals’ habitats to try to kill them. Pacific salmon aren’t often mentioned alongside Roosevelt’s elephants or Hemingway’s tigers, but in Tucker Malarkey’s Stronghold (Random House, $28), fish is the biggest game of all. Malarkey’s protagonist is a charming misfit named Guido Rahr, who also happens to be her cousin. A naturalist almost as soon as he could walk, Rahr got hooked on fly fishing in his late teens, only to realize, to his horror, that the hydroelectric dams, agricultural runoff, commercial fishing industry, deforestation, and climate change in the Pacific Northwest could bring wild salmon to extinction.