This is the story of a research project that is akin to a nested doll: an experiment run on data generated by another experiment.
Thomas Quinn at the University of Washington in Seattle and his colleagues survey sockeye salmon (Oncorhynchus nerka) carcasses in a small stream in southwestern Alaska. As part of a study of salmon consumption by bears, team members scoop dead fish out of the stream to count them and, to prevent double-counting, throw each recorded carcass into the forest.
Starting in 1997, the salmon-counters threw fish only onto the left-hand bank. Quinn wondered whether the white spruce trees (Picea glauca) on the banks where the dead salmon were discarded would grow faster, thanks to all the fishy fertilizer.
The researchers examined spruce needles from trees on the left bank and found elevated levels of a heavy form of nitrogen found largely in marine ecosystems — showing that nutrients from the sockeye, which spend much of their lives at sea, were making their way into the trees.
The scientists also saw a rise in the growth rate of the left-bank spruces, dating from the beginning of the salmon-tossing protocol.