Salmons from two rivers are reducing in size due to lack of food
salmons from two rivers have shrunk in size due to a decades-old fight for food in the Gulf of Alaska. This was discovered by scientists at the University of Alaska Fairbanks, usa, who used high-resolution digital imaging equipment to look at about 2,000 fish scales taken from chum salmon caught on Alaska's Yukon river and Russia's Anadyr river over more than 30 years. The us National Marine Fisheries Service, the Alaska Department of Fish and Game and the Russian Pacific Fisheries Research Centre also participated in the study.
Scientists used a digital camera and a dissecting microscope to analyse acetate images of scales. The scales were taken from the archives at the Alaska Department of Fish and Game. These scales were taken from Yukon River's chum salmon captured at test sites in the lower regions of the river. This collection dates back to 1960. The Russian Pacific Fisheries Research Centre collection used for the analysis is much older. Scientists looked at acetate impressions of the scales made for long-term storage. The impressions, which look a lot like human fingerprints, were made by pressing the scales' bony ridges onto sheets of acetate.
By looking closely at the width of the scales, scientists determined that chum salmon decreased in size by about 25 per cent between 1965 and 1997. While it has been known for years that the size of Pacific salmon has decreased, the study reveals just when growth slowed during the life cycle of the fish. It found that the fish grew well in the first year of life, but growth rates decreased when the fish foraged for food in the Gulf of Alaska before returning to rivers to spawn. "These fish have grown more slowly as young adults at age two, three and four," said William Smoker, director of the School of Fisheries at the university and lead investigator for the three-year, us $262,000 federally funded study.
However, there are some researchers who opine that genetic changes could be another factor responsible for the shrinking sizes. According to Buel D Rodgers, an instructor of medicine at Johns Hopkins University's School of Medicine, the preference for larger fish by commercial and sport fisherfolk could be removing the bigger fish from the gene pool, leaving only the genetically smaller fish to reproduce (www.dailynews.yahoo.com, December 15, 2001).
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