Course:EOSC311/2024/How Salmon Spawning is affected by Natural Geology

Introduction to Salmon Spawning and Class Connection

Chinook salmon swimming upstream in shallow waters

Salmon are magnificent fish that go through some absurdly different life histories than other fish. Something quite unique about them though, is that whilst spawning, the adults adapt from saltwater to freshwater. These adaptations can be both behavioural and physiological. Female salmon tend to only change in colour, whereas males undergo radical changes. You may have heard of sockeye salmon gaining a hump; furthermore, although that feature is mainly unique to sockeye, other salmon species develop a longer, curved mouth referred to as a kype that contains larger canine teeth.

Beyond the transition of being a saltwater fish to one that is freshwater, salmon spawning refers to the process that as the salmon adapt to their changed environment, they must travel upstream in search of an appropriate place. Calmer, less turbulent waters typically promote incubation due to fewer natural disturbances and are placed further from predators that would otherwise find a free meal, ensuring survival rates.

I used this project to paint a line connecting my major, applied animal biology, and how it can be related to this course of Earth and its resources. This was done by asking how geology affects spawning seasons for salmon. Although seemingly very vague at first, the modules I used to help conduct my project were Module 2 - What's in my cell phone? and Module 4 - Water, what is it good for? This topic was also inspired by news articles appearing stating that salmon are killed en masse in the British Columbia area, not having anything to do with predators but mostly because they just did not make it to their spawning grounds.

Landslides being a Factor that Prevents Spawning

Landslide that occurred at Big Bar, BC in 2019.

In general, many have heard from the media, such as news outlets, that temperature plays the predominant role in the reduction of yearly salmon spawning events. Hot summers often lead to river banks that run dry which as one would expect, means a lot of dead fish. While temperature does play a role, geology's contribution to the matter should not be understated. Habitat connectivity could affect future generations, but the geological factor of landslides negatively affect the rate of spawning. An example of this is that in 2019, the Fraser Valley (specifically Big Bar) experienced a landslide, which instantly turned a what would be calm stream into very turbid waters. The submerged debris modified the gradient of the stream's depth, which affected its velocity and discharge rate.

Why don't salmon just adapt to their situation and start spawning more downstream to avoid the turbulent waters? One of the main reasons is that salmon have specific requirements for spawning grounds, such as an appropriate gravel bed substrate, adequate water flow, and good water quality. Spawning salmon are also driven by instinct, more of than not returning to the precise location where they were born. This instinct is seemingly hard-programmed into the salmon and is a researched field to study salmon behaviour. This instinct is also what prevents salmon from doing massive jumps to get over these newfound landslide shaped obstacles. Jumping from lower elevation to a higher one seen at small waterfalls while being familiar with area is different from not knowing what pathways or complex barriers landslides bring.

If they did overcome the prior mentioned instinct, offspring and fry survival would not likely be very convincing whatsoever due to the lingering causes and effects of landslides.

Possible Causes that Impede Spawning

Spawning downstream would lead to eggs being littered with sediment which can imply negative developments such as damaged eggs becoming unviable or fry with abnormalities. After landslides, torrents of debris bring foreign sediments that imbed themselves into the watershed which can create more narrow corridors, causing faster moving water to flow through, in turn carrying more and larger sediment.

Landslide that occurred at Mount Meager, BC in 2010, which is nearby to Lillooet River, a critical habitat salmon pass through on the way upstream.

Besides damage caused to the eggs, high sedimentation reduces the capacity for eggs to intake oxygen. Assuming a salmon managed to find a suitable gravel bed for the eggs, introduced sediments can alter the microhabitats that eggs require to develop. Sedimentation can clog the gravel beds or compact them due to the accumulated weight of sediment, reducing flow of water and therefore their oxygen supply. A sediment layer may form on top which if you know about swamps and marshes, creates a hypoxic environment, low in oxygen which is fatal.

Salmon disappearance in recent years has increased dramatically and although landslides are definitely not the sole cause, rivers and streams with a lot of sedimentation do not make the travel upstream any more enticing for salmon, especially in combination with the disrupted and degraded habitats that come along with landslides. Much of the cause is due to changing river temperatures to be both rising and unpredictable. Salmon management companies don't even have the opportunity to do their jobs since there are so few salmon to manage.

So amidst all of the disarray, what solutions exist to combat landslide sedimentation or salmon disappearance?

One of the solutions of landslide sedimentation was to physically lift salmon using a helicopter. This was made directly in response to the Big Bar landslide along the Fraser River. A dugout was made to isolate some salmon at a time and a pathway was partitioned to help make a calmer route for the salmon -- from there, salmon either moved upstream on their own or were picked up by helicopter to be dropped upstream where it is much less turbulent.

By far the most well known solution was to raise salmon in fisheries. Public criticisms aside, artificial propagations of salmon are often used to supplement fish stocks of areas affected by something like landslides or rapid population decline. Along with attempting to keep population levels stable, hatcheries allow for research and monitoring and often coincide with efforts of habitat restoration projects. As mentioned above, there are public criticisms and that mainly shows how hatcheries are nowhere near perfect, with tons of room for improvement. Genetic diversity is a big factor in that many of the fish raised in hatcheries lack it. Behavioural differences also may make hatchery fish be less attuned to migration patterns and more prone to predator attacks, reducing overall fitness. Lastly, the amount of economic burden this puts has not reflected in the amount of salmon populations expected to have bounced back.

Image of a salmon jumping upstream heading towards spawning grounds, Brooks Falls

Conclusion and Overall Thoughts

As someone who has little to no background information about geology, it was really assuring to write on this topic and connect it with my major in animal biology. I have never previously thought of water as being geology related but when it came to covering an issue, I knew I had to connect it with something I am passionate about. Hence the topic of salmon and how they are being geologically driven out of their spawning grounds. It was really eye opening to see the damage that sediment can cause as well as the obstacles it can pose. Landslides create lasting effects that cannot simply be avoided and must be worked around, they can create environments of fast moving turbulent water or imitate the hypoxic nature of swamps.

Thinking ahead, there are many instances of people wanting to monitor in case problems may arise to prevent them. Although I have only this course under my belt, I would want to use that knowledge to modify something like bodies of water such that they would favour spawning salmon, instead of monitoring for landslides, action could be taken to prevent them from occurring in large scale as the one at Mount Meager, or even Big Bar. The main issue I would be tasked with would be economically related since I would be fighting and suggesting ways to change how salmon swim upstream only to return them to how they were before declining in population. Gravel substrate? Salmon already needed that. Calm waters? Should be a given. The next step would be implementing what I have learned in this course such as relating salmon spawning runs to hydropower or even a topic from a different module which I would not have thought of before.

References

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