Fish sex might not seem very consequential, but countless couplings over the course of millennia can leave a mark on the landscape. In a recent study, researchers modeled how spawning affects rivers in the Pacific Northwest and concluded that salmon sex actually helped to carve the region’s mountainsides.
Salmon return from the sea to the rivers and streams of their birth to reproduce. Once a female finds a spot with the right size rocks or gravel, she digs a pit for her eggs. After the male fertilizes them, the female digs another hole upstream and covers her brood with the sediment from it. Her excavation erodes the streambed by making it easier for sediment and gravel to move downstream, says study co-author Alexander K. Fremier, an aquatic ecologist at Washington State University.
Fremier and his colleagues collected data on salmon-caused erosion rates in an experimental stream and extrapolated their findings to real rivers over millions of years.
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