At both the alevin and redd stage the salmon have a yolk sac attached to provide nutrition, but once they transition to the fry stage they become predators. Fry form territories in shallow pools and fight for their preferred habitats against other fry. At this stage the salmon require a healthy habitat with lots of vegetation as the number of predators increases. Abundant vegetation aids the fry in providing various hideouts from their predators. Whereas increased sunlight can lower the oxygen concentrations, decreased sunlight due to reflective sediment leads to reduced aquatic plant growth.
At adult stage once the salmon have entered the ocean they fall prey to various species despite their camouflaged outer layer. Their largest predator being, us, humans. Salmon have little to no defenses against human predation. Various salmon species spend a huge range of time out in the ocean. As for Chinook, they spend about 3-5 years. After this time period the salmon head back for the native streams, lakes, or rivers. Little is understood about the mechanism that leads these salmon back to their birthplaces, but it is believed that the use their chemical memory and the olfactory system to guide them back home. They head back to the same estuary and go through smoltification in order to adjust to the freshwater. Once again the health of the estuary is crucial to the survival of the adult salmon. The water temperature, salinity, and pollutant levels all play a role in determining whether an estuary is healthy or not. Once they begin to move upstream adult salmon face the biggest barrier of all, man-made dams. Also, they fall prey to humans, otters and bears at this stage.
1."Why Is Salmon Conservation Important?" Wild Salmon Center. Web. 06 Mar. 2012. <http://www.wildsalmoncenter.org/about/whySalmon.php>
2. "Salmonid Life Cycle." Center for Social and Environmental Stewardship. CFSES, 2005. Web. 3 Mar 2012. <http://www.cfses.org/elearning/tutorial.htm>.
3.United States. NOAA. Pacific Salmon & Steelhead: A Natural Wonder. C.A.: , 2010. Web. <http://swr.nmfs.noaa.gov/recovery/salm_steel.htm>.
4. "Salmon running the gauntlet: Salmon lifecycle." PBS. Thirteen- Educational Broadcasting Corporation, 2011. Web. 3 Mar 2012. <http://www.pbs.org/wnet/nature/episodes/salmon-running-the-gauntlet/video-full-episode/6620/>.