Salmon
are vulnerable throughout their whole lives to water temperature but it has
the most considerable effect on salmon in the early stages of life. Temperature can have a large effect on the mortality rate as well as the sex ratio of the kokanee for a spawning cycle. The average
temperature of Lake Sammamish has been increasing at an alarming rate over the
past few decades (kingcounty.gov). This is thought to be one of the main contributing factors
to a decrease in local kokanee populations. A study done on kokanee salmon in British Columbia found that water temperatures above 14ºC can
kill the kokanee salmon eggs (Dill). There has also been recent research on the relationship between temperature and the sex ratio of salmon. It has been shown that the determination of sex is
temperature dependent in sockeye salmon, and increasing water temperatures
during and shortly after hatching can reverse genetic females into males (Azuma). The males are still functioning and can successfully reproduce, but a disproportionate ratio of males to females will only
exacerbate the problem of declining kokanee numbers.
Adult salmon are also affected by water temperature. They rely on normal levels of oxygen in the water in order to be able to perform basic metabolic processes and efficiently move to search for food and away from predators. Because oxygen saturation
levels in water decrease as temperature increases, there is less available
oxygen in warm water than cold water (Dejours). Therefore, salmon are found to receive lower levels of oxygen
in warmer water and become fatigued much more quickly. The salmon will eventually stop swimming in a water temperature of 24ºC (Steinhausen). This can have a detrimental effect on their
ability to search for and eat food.
(Berge)
This graph shows the fluctuation of water temperature compared to depth throughout the year in Lake Sammamish and the corresponding dissolved oxygen. During the summer months, salmon must go deeper in the lake in order to find cooler temperatures.
Besides directly affecting salmon in their survivability, water temperature also
influences plants that the salmon depend on for cover from predators as well numbers of zooplankton which are the main staple of the adult salmon diet
(Dill).
Below is a graph relating the escapement estimates of late run kokanee salmon of the Lake Sammamish tributaries from 1996 to 2012 to the average water temperature in June from 2001 to 2011. The escapement estimates are the number of salmon that successfully survive and return to their original hatching grounds to spawn. The water temperatures were taken from the King County website and are collected by a buoy in south Lake Sammamish. The average temperature in the graph is at a depth of 10m. This is due to the fact that the salmon's main food source in the lake, the zooplankton Daphnia, is generally found near this depth and the water temperature is cool enough that salmon can feed at this depth, even during most of the summer months. From a depth of 0-10m there is a higher density of Daphnia as well as a higher rate of consumption by kokanee than from 10-20m (Berge). The temperature of interest is in June because almost all kokanee salmon in the Lake Sammamish Basin will have migrated into Lake Sammamish at this time which coincides with the fact that June is a time of an annual spike in the number of Daphnia (Berge). This is an important time for the salmon as it offers a large availability of food and therefore a good growth opportunity for the salmon.
Below is a graph relating the escapement estimates of late run kokanee salmon of the Lake Sammamish tributaries from 1996 to 2012 to the average water temperature in June from 2001 to 2011. The escapement estimates are the number of salmon that successfully survive and return to their original hatching grounds to spawn. The water temperatures were taken from the King County website and are collected by a buoy in south Lake Sammamish. The average temperature in the graph is at a depth of 10m. This is due to the fact that the salmon's main food source in the lake, the zooplankton Daphnia, is generally found near this depth and the water temperature is cool enough that salmon can feed at this depth, even during most of the summer months. From a depth of 0-10m there is a higher density of Daphnia as well as a higher rate of consumption by kokanee than from 10-20m (Berge). The temperature of interest is in June because almost all kokanee salmon in the Lake Sammamish Basin will have migrated into Lake Sammamish at this time which coincides with the fact that June is a time of an annual spike in the number of Daphnia (Berge). This is an important time for the salmon as it offers a large availability of food and therefore a good growth opportunity for the salmon.
The red line is escapement estimates of kokanee from Lewis, Ebright, Laughing Jacobs and Pine Lake Creeks. The green line is the temperature of Lake Sammamish at a depth of 10m in June. (Re-establishment efforts of releasing hatchery kokanee into the creeks explain large spikes in kokanee population after low numbers the previous year.)
Although this graph does not prove any causation of water temperature on kokanee populations, it, along with the effects that temperature can have on salmon throughout their life should prompt concern. There are many factors that influence the kokanee population, but combining research done in the area of connections of salmon and water temperatures with the visual of this graph, there seems to be some sort of inverse relation between temperature and kokanee numbers. More research needs to be done in Lake Sammamish in order to see if there is a significant correlation between water temperatures and kokanee population, or if it is only an illustration of another factor.
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