Salmon: Not Just A Tasty Treat

Why are salmon so important? I myself was wondering why we should put so much energy and money into conserving the salmon population until I began to look at what the effects would be if they were gone. Native Americans believe that the return of the salmon each year represents the continuation and prosperity of all life. In a way this is true. Salmon are sensitive to their environmental conditions and their returning numbers depend on these conditions. Salmon bring a large biomass to the freshwater and terrestrial ecosystem. Their carcasses provide phosphorus to the land which is spread out by large apex predators, such as eagles and brown bears.  The carcasses also provide food for small invertebrate (whose presence indicates good water quality) which in turn are food for the juvenile salmonids.  When there is a decline in the number of salmon it indicates that our ecosystem is also declining.  This, however, is not the only reason we should care about salmon. A primary food source for most people and the jobs that are created from the salmon industry are in danger if we are to let the salmon population disappear. Thousands of individuals are employed each year in the salmon industry, and bring in millions of dollars in profits. The fate of salmon lies within us to try to restore our ecosystem, preserve our cultural heritage, and see to it that thousands of individuals keep their jobs.

 

The life cycle of the salmon begins in the gravel beds of streams where about 2,000-10,000 eggs (depending on the species of the salmon) are laid and fertilized. These eggs depend on a good oxygen flow from the stream in which they are laid in order to survive to adult hood. After about one to three months the eggs hatch to become alevins which feed off of their yolks sacs and rely on small pools within the stream to seek cover from predators. The salmon then become fry which live in small pools in the stream seeking small invertebrate for food and shading for shelter. The salmon must then be able to make the journey from freshwater to salt water in which they need to undergo a process known as smolting which occurs in an estuary. A smolt migrates to the ocean by rivers and can spend years in the ocean before returning to spawn. A spawning salmon will most likely return to the stream in which they themselves hatched, but there can be straying into other streams to spawn as well. After the spawning adults have laid and fertilized their eggs they will die usually within two weeks, although steelhead can return to the ocean after spawning.

A salmon population is part of a metapopulation. These metapopulations work together in asynchrony to create a viable dispersal of salmon. A study done in 2011* (Fullerton et al.) in the Oregon area on Chinook and steelhead salmon tested the effects that human activities have on the spatial structure of these salmon populations in the Pacific. The study compares the historical metapopulations against current possible situations of metapopulations shown in the figure below. The historical metapopulation assumed only natural barriers limited by fish access to streams; fish were of wild origin; and habitat quality and fish abundance were minimally affected by human activities. There were four  scenarios that were tested: restricted access (access to streams limited to areas below impassable hydropower dams, but other conditions remained as in the historical scenario); reduced habitat quality (fish restricted to areas below dams and instream habitat quality decreased relative to historical conditions); presence of hatchery fish (fish restricted to areas below dams and an increased probability of dispersal by hatchery fish relative to dispersal rates of wild fish); and myriad (multiple factors, including restricted stream access due to dams, reduced habitat quality, presence of hatchery fish, fish harvest, unfavorable oceanic conditions, and other unknown environmental factors).  Two other scenarios were introduced into the study: recolonization and preservation shown in the bottom of the figure below.

The figure to the above shows (a), that represents possible metapopulation spatial structures, and (b) which illustrates the spatial structure of salmon metapopulation resulting from the scenarios listed above. The black circles are populations that if recolonized would yield the largest increases in connectivity and the open circles are existing populations that would most disconnect the graphs if not preserved. The solid lines are existing connections while the dashed lines show the past connections. The circle sizes relate to the size of the population, and the ones that are boldly outlined are populations that need to be reestablished or preserved. This graphical analysis is useful when looking at which subpopulation of the entire metapopulation would have the most detrimental effects when exposed to human activity.

The overall experiment demonstrated situations in which the majority of the connectivity between the subpopulations in the metapopulation remained high and stable. Connectivity of the metapopulation as a whole is important because it increases the diversity of the salmon and increases the likelihood of survival when the environment changes or a disaster occurs. The connectivity and the variance within the study showed that the Chinook (fall and spring) and winter steelhead decreased with the addition of large hydropower dams and when there was a decrease in the habitat quality. The majority of the connectivity of the steelhead was due to the high stray rate from one population to another. High connectivity between the subpopulations was enhanced in general when salmon were straying indicating that it is necessary in a metapopulation and becomes much harder when there is restricted access to these areas. Hatcheries on the other hand increase the connectivity of the populations by introducing salmon into the metapopulation. This is due to the high stray rate of the salmon which occurs because they do not have a strong connection with their spawning stream. The myriad scenario is a scenario that is most like today’s salmon metapopulation, and represents the panmicitic populations shown in the figure where there is random mating between all the populations. This is un-favorable because there is a decrease in the amount of genetic diversity in the metapopulation which makes all of the salmon susceptible to any infection or disease or any adaption to environmental change.

Salmon populations not only rely on the connectivity throughout the metapopulation, but yet the asynchrony in these populations that is beneficial to the environment. The asynchronous pattern of salmon allows salmon to be introduced into the ocean at all times of the year from different populations. In a metapopulation context, asynchrony decreases global extinction risk and increases persistence time (*Heino et al. 1997).  The best example of asynchrony is seen and described in a study done by Lauren A. Rogers and Daniel E. Schindler, where they examined what the causes for asynchrony were. The results were: the importance of maintaining diverse spawning and the need for habitat conservation. Studies like these are vital because they  inform us of the necessary information and actions that we need to take in order to be able to help the salmon population survive and return to their spawning streams.

Overall, the conservation of the salmon population is important to all of us because we are linked to them culturally, they provide an indication about the state of our habitat, and without them thousands of jobs would be lost and there would be no tasty salmon to go around. This can be achieved through the conservation of metapopulations, but in a way that reserves the diversity of the salmon. Dispersing salmon from hatcheries is not the only way, and can be disruptive to the genetic diversity. With this knowledge of stray rates of hatchery fish we can better improve the rates of dispersal within a metapopulation to maintain that diversity. Maintaining habitats and removing or improving some of the hydropower dams will be beneficial towards the salmon population. Habitats can be improved by protecting or restoring areas that support the larger subpopulations, and logging can be reduced around main spawning streams. Salmon are still listed on the Endangered Species Act and are a main part of the way we live here in the Pacific Northwest; action must be taken to ensure that they will be here for many more generations.

Images:

1."Stepping up for Salmon 0." Stepping up for Salmon « EcoWatch: Uniting the Voice of the Grassroots Environmental Movement. Web. 06 Mar. 2012. <http://ecowatch.org/2011/stepping-up-for-salmon/>.

2.http://images.nationalgeographic.com/wpf/media-live/photos/000/007/cache/sockeye-salmon_715_600x450.jpg

3.http://www.idahoforests.org/img/salmon02a.jpg

References:

1."Asynchrony PlayV2('en/US/st/stdjsfs5sjdyd3stssssyhh5h5');playV2('en/UK/st/stdjsfs5sjdyd3stssssyhh5h5')." TheFreeDictionary.com. Web. 06 Mar. 2012. <http://medical-dictionary.thefreedictionary.com/asynchrony>.

2."Basic Information about Estuaries." Home. Web. 06 Mar. 2012. <http://water.epa.gov/type/oceb/nep/about.cfm>.

3.*Fullerton, Aimee H., Steven T. Lindley, George R. Pess, Blake E. Feist, E. Ashley Steel, and Paul McELHANY. "Human Influence on the Spatial Structure of Threatened Pacific Salmon Metapopulations." Conservation Biology 25.5 (2011): 932-44. 

4. *Heino, M. et al. 1997. Synchronous dynamics and rates of extinction in spatially structured populations. Proc. R. Soc. Lond. B 164: 481-486

5."Learn More." CRITFC. Web. 06 Mar. 2012. <http://www.critfc.org/text/salmcult.html>.

6."The Life Cycle of a Salmon." Seymour Salmonid Society and the Seymour River Fish Hatchery. Web. 06 Mar. 2012. <http://seymoursalmon.com/lifecycle.php>.

7."Panmictic Definition." Web. 06 Mar. 2012. <http://groups.molbiosci.northwestern.edu/holmgren/Glossary/Definitions/Def-P/panmictic.html>.

8.Rogers, Lauren A., and Daniel E. Schindler. "Asynchrony in Population Dynamics of Sockeye Salmon in Southwest Alaska." Oikos 117.10 (2008): 1578-586.

9."Salmon Reproduction." Salmon: Reproduction. Web. 06 Mar. 2012. <http://www.marinebio.net/marinescience/05nekton/sarepro.htm>.

10."Smolting - Adjustment to Saline Water:." Web. 06 Mar. 2012. <http://www.holar.is/~aquafarmer/node21.html>.

11.Thompson, John N. "Metapopulation (ecology)." Encyclopedia Britannica Online. Encyclopedia Britannica. Web. 06 Mar. 2012. <http://www.britannica.com/EBchecked/topic/377988/metapopulation>.

12."Why Is Salmon Conservation Important?" Wild Salmon Center. Web. 06 Mar. 2012. <http://www.wildsalmoncenter.org/about/whySalmon.php>.