by Greg Kornelis
The Raincoast Conservation Foundation (RCF) of British Columbia is working to understand the intricate and numerous connections between salmon and the keystone species they support. Lacking consideration in the management of B.C. fisheries, the affects of over harvesting and declining returns of salmon on grizzly bear and orca whale populations are the focus of the RCF Salmon for Wildlife Initiative. A recent research publication in PLoS ONE shines light on the connections between dietary salmon and grizzly bear health.
According to new research, declines in salmon abundance over the years can have negative consequences for grizzly bears’ stress and reproductive health. Throughout their evolution, coastal grizzly bears have relied on the returning salmon every fall to pad out their fat stores for the winter hibernation ahead. With the reduced returns of chinook salmon and other species, it is more important now than ever to understand the relationship between dietary salmon and grizzly bear fitness. Biologist Heather Bryan (RCF) analyzed the stress and reproductive hormone concentrations in coastal and inland grizzly bears to see just how they are connected to the fall salmon runs.
By measuring stress and reproduction hormone levels in the grizzly’s hair (from hair snags), Bryan was able to see how the hormones could be affected by availability and abundance of dietary salmon. For example, coastal grizzly bears (who eat salmon) were found to have higher concentrations of testosterone than interior grizzlies (who don’t eat salmon). More testosterone is important for mate acquisitions, food competition, and cub protection. The levels could be due to the need for dominance hierarchies at streams with high population densities – which are made possible by returning salmon! Amongst the coastal grizzlies, it was found that higher salmon consumption resulted in lower concentration of the stress hormone cortisol. This result wasn’t too surprising however; just imagine walking to your fridge in the middle of the night and finding it empty! Would you be more stressful or less? Chronically high amounts of stress hormone can have negative affects on health, reproduction, and social interactions too.
The more we learn about how salmon abundance affects hormone levels in grizzlies and how those hormone levels affect fitness, the better informed we will be when it comes to integrating grizzly welfare into our fisheries policies and conservation efforts. You can find the article at: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0080537
Bryan HM, Darimont CT, Paquet PC, Wynne-Edwards KE, Smits JEG (2013) Stress and Reproductive Hormones in Grizzly Bears Reflect Nutritional Benefits and Social Consequences of a Salmon Foraging Niche. PLoS ONE 8(11): e80537. doi:10.1371/journal.pone.0080537