Every year Vancouver resident Stephen Ottridge takes hamburgers or steak to his street's annual summer block party. This year, against the backdrop of what looks to be the biggest sockeye salmon run in almost a century in the nearby Fraser River, he arrived with a salmon large enough to fill the whole barbecue, according to Reuters. "There is a cornucopia of salmon this year, so we decided to treat the block to some," Ottridge said from the city on Canada's Pacific Coast, where marine experts are both puzzled and delighted by the unexpected glut of the bright-red, succulent fish. After years of declining sockeye numbers and a struggling fishing industry, the Pacific Salmon Commission last week said it now expects 25 million sockeye will return to the Fraser River this year -- more than double its earlier forecast and the best run since 1913. Last year, slightly more than a measly 1 million sockeye made their way back to their spawning grounds, prompting the Canadian government to close the river to commercial and recreational sockeye fishing for the third straight year. The reasons for the salmon bonanza remain a mystery, but what has helped is that it has coincided with a "dominant-run" year, said Carl Walters, a fisheries expert at the University of British Columbia's zoology department. "Every fourth year is the dominant year when the biggest run comes in. The year after that is sub-dominant. Then you get two really low runs," Walters told Reuters. Twenty years of declining sockeye in the Fraser River led the Canadian government to launch an investigation last year into the disappearance of the fish at a time when numerous theories abound. These include that climate change may be reducing food supply for salmon in the ocean, and that rising temperatures in the river may have weakened the fish. Commercial fish farms that the young Fraser River salmon pass en route to the ocean have also been blamed for infecting them with damaging sea lice, a marine parasite. While consumers are enjoying cheap salmon for the first time in years -- prices for fresh sockeye are down about 30 percent from a year ago -- the fishing industry is struggling to cope with the sudden bounty. "It is an amazing thing but the problem is that this has come along when the market has been lost. Now we have all this fish and we can't do a lot with it," said Bob Fraumeni, owner of FAS Seafood Producers, which operates a West Coast commercial fishing fleet and retail outlets. There are reports of fish rotting on boats as fishermen run out of ice and freezer space, and of tempers flaring as boats jostle for space on the water. For now though, most are enjoying the bumper harvest. "I've been in the business for 20 years and I've eaten sockeye from everywhere and this is, in my opinion, the best-tasting Canadian sockeye around," said George Heras, president of family-owned Seven Seas Fish Market in Vancouver.