Fraser River sockeye salmon: data synthesis and cumulative impacts

Seasonal population distribution patterns show highest concentrations at the northern tip ofVancouver Island in summer. The much larger males eat 15 – 35 kg per day and salmonrepresents 17% of their diet (third highest contributor). Their major food source is forage fish(sandlance, herring and sardines are believed to be driving the population increases). Mostsalmon are found in their diet in the fall and those are mostly adults. There are differentproportions of salmon in summer diets by region (North Danger Rocks has the highestproportion of salmon at over 35%). Overall, for Southern BC and Washington State (CapeCaution to the Columbia River), salmon comprised 10% of their overall diet. They primarilyprey on adult-size salmon from all 5 species of salmon and steelhead, but mostly focus on pinkand chum. Sockeye comprises the smallest proportion of all salmon species eaten. A 2009 studycovering BC and the Eastern Aleutians found sockeye represented 9% of total salmon in the dietof Stellar sea lions. Unpublished data from Olesiuk et al for Southern BC and Washingtonconfirmed sockeye was the prey in just 5% of all salmon DNA diet samples.Harbour seals: Historical populations are thought to have been in the range of 80,000 to100,000. Hunting and culling significantly reduced those numbers, but a steady increase hasbrought those numbers back to historical levels. Distribution patterns show they stay close tohome, all around the BC coast, and they eat around 1.9 kg per day. Scat studies in the 1980sshow salmon was only 4% of their diets. The species of salmon eaten is unknown but DNAtesting could reveal that if the samples are still there. Populations tend to be largest in estuarieswith large chum and coho runs. They appear to eat mostly adult salmon, although two areas(Comox Harbour and Port Moody) reported high numbers of chum and coho juveniles in scats.California sea lions: The big males come north in the fall, and some move into Georgia Strait inwinter with the herring. But only about 3,000 of the total 240,000 California sea lion populationreaches BC waters. Their BC diet is unknown, but likely similar to that of Stellar sea lions. Theyare also not present in the summer.Northern fur seals: Stomach samples in the 1950s and 1970s indicated a diverse diet but did notfind any sockeye.Killer whales: A 2006 study observed 423 salmon kills occurring between May and December,but they seem to specialize in Chinook. Only one of the salmon killed was a sockeye.Other species: There is no significant evidence of sockeye predation among other marinemammals such as minke and humpback whales, elephant seals, porpoises and dolphins.Why killer whales don’t eat more sockeye is unknown. Perhaps it relates to quality, swimmingspeed, inconsistent returns, or return timing coinciding with other options during a limitedwindow.Fish & bird predation on Fraser sockeyeVilly Christensen, UBCThis report addresses fish and bird predation (neither were addressed in the PSC report) in thefreshwater and estuarine environment, Georgia Strait, Queen Charlotte Sound/BC and theNortheast Pacific Ocean. There is no doubt that sockeye are eaten in large numbers out in theocean, but there has been very little study of what’s eating them out there.A few hundred previous studies were looked at, but very few relate to sockeye predationmortality at different life stages. Key metrics include diets (most diet studies are only55