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SOURCE: Science

DATE: August 20, 2019

SNIP: One day in June 1919, workers in a busy Canadian cannery in Port Essington rushed to clean, cook, and can the bright red flesh of a huge number of sockeye salmon hauled from the nearby Skeena River. Watching the frenzy was a government “fisheries overseer” named Robert Gibson. Periodically, Gibson selected a fish, scraped off a few scales, and affixed them to the pages of a small notebook using the salmon’s own slime. Next to each sample—he collected a total of 125 on this day—Gibson wrote the weight, length, sex, and catch date. A U.S. fish biologist hired by British Columbia would follow up by calculating each fish’s age with the then-new technique of using a microscope to count the growth rings visible on the scales, much as botanists age a tree.

Over more than 3 decades, from 1912 to 1948, Gibson and colleagues filled dozens of notebooks with fish scales from the Skeena, Canada’s second-largest salmon river. Ultimately, however, the records were dumped in a box and largely forgotten.

Until now. This week, scientists unveiled a study that makes clever use of the fish DNA preserved in the battered, smeared books to reconstruct how wild Skeena salmon have fared over the past century. The conclusion is sobering: Declines have been more precipitous and widespread than previously understood, with the river’s 13 major wild sockeye salmon populations plummeting by 56% to 99% over the period from 1913 to 2014, largely because of overfishing.

The notebooks were rediscovered 23 years ago in a Vancouver, Canada, office—but only recently analyzed. They have provided a rare “window into the past,” says biologist Michael Price, a doctoral student at Simon Fraser University in Burnaby, Canada, and the lead author of the study, published 20 August in Conservation Letters.

Overall, the number of wild sockeye salmon returning to spawn in the Skeena has dropped by about 75% since the early 1900s, falling from some 1.8 million annually to 470,000, the researchers conclude. And they find that all 13 of the river’s stocks have shrunk—in contrast to previous studies, which used sockeye numbers from the 1960s as a baseline and found just seven of the runs had declined in recent decades. Several wild stocks are nearly extinct. A population that once thrived in the Motase Lake watershed has declined from about 40,000 spawning fish annually to just 600.