Science Discussion: Why You Should Care About Wetlands – Salmon is Tasty

Obviously I care about wetlands. I’m spending the next 5-ish years going to school to get a degree that says “This chick really likes wetlands and knows a whole lot about them!”

But why should you care about them?

There are so many reasons to care about wetlands that I cannot possibly talk about them all in one post (well, I could – but that’s basically what my dissertation will be and I don’t know many people who actually want to read a dissertation in their free time).

So today I’ll only talk about one of the many important roles of wetlands that makes a difference in our everyday lives.  Do you occasionally enjoy a delicious cream cheese and smoked salmon bagel for breakfast, or maybe some grilled Teriyaki salmon for dinner? For the vegetarians out there: do you know someone who enjoys these things? If you answered yes to either question, then you should care about wetlands because salmon populations need wetlands to survive, and beaver dams are directly responsible for the creation of many of the wetlands that salmon rely on!

Do you like this? Does your friend like this? Then you should like wetlands and beavers too!
Do you like this? Does your friend like this? Then you should like wetlands and beavers too!

Alright, that was a big statement to make and some of you may be thinking, “hold on a minute, Emily. I’m not following. When I think of salmon, I think about these gigantic salmon swimming up whitewater rapids and spending most of their lives in the ocean.  I do not think about wetlands, and definitely do not think of beavers.” I totally understand that associating salmon with wetlands is non-intuitive, so let me explain.

Only have 5 minutes to read? Here is the short answer to why do salmon need wetlands to survive.
It’s true that the most iconic images of salmon is them forcing their way up treacherous, fast moving rivers and streams. This is called a “salmon run,” and typically occurs in late summer and early fall when stream flows are lowest. Salmon runs are so difficult, that every single mature salmon in the run will die after they have accomplished their goal. What could possibly be important enough for the salmon put themselves through that incredibly difficult, and ultimately deadly journey in the first place? The salmon run is how they get to their spawning grounds and make baby salmon. What are their spawning grounds? Inland waterways that are downstream of wetlands. Where do those wetlands come from? In a lot of cases, beaver dams obstructing the streams.


Have more time? Want more details?
For those of you that don’t want to just take my word for it, or want to learn more about the salmon-wetland-beaver relationship, here is a more thorough explanation.

Salmon Need to be Able to Reach the Spawning Ground in the First Place
A lack of rainfall can hurt salmon spawning. If there is not enough rain one year, streams can go dry and (this part shouldn’t come as a surprise to anyone) salmon can’t swim up a stream to lay eggs if there is no water to swim in. Luckily, wetlands can prevent streams from going dry when there is a lack of incoming water. How do they do that? Imagine a creek upstream generic wetland – that creek is probably flowing at a visibly quick pace in a fairly narrow channel. Once that fast moving creek hits the wetland, it slows down.  This is because now instead of having only a narrow channel to fill, it has a comparatively wide wetland environment to spread out in! In order for the wetland to not just grow out of control, there needs to be an outlet (such as another creek or stream) draining some of the water downstream.

A cool picture showing how a beaver dam makes a wetland. On the righthand side of the aerial photo you see a stream flowing to the left. The arrows are pointing to a 70 meter long beaver dam on that stream. Notice the wide wetland that formed upstream of the dam. Also take note of the stream to the left of the dam discharging water from the beaver-created wetland.
A cool picture showing how a beaver dam makes a wetland. On the righthand side of the aerial photo you see a stream flowing to the left. The arrows are pointing to a 70 meter long beaver dam on that stream. Notice the wide wetland that formed upstream of the dam. Also take note of the stream to the left of the dam discharging water from the beaver-created wetland.

Because the wetland is both fed water by the upstream flows and discharges water downstream, it can be thought of as a reservoir. When there is plentiful rain, it simply slows the upstream flow and maybe gets a little deeper or wider.  When there isn’t enough rain, the wetland will still slowly release its stored water into the downstream system even if there is nothing feeding it from upstream. It can continue to discharge water downstream until the entire wetland is dry (which doesn’t happen often, especially when the wetland is fed by both rainfall and groundwater). Having wetlands act as water storage tanks ensures that the streams continue to flow through times of drought, and that mature salmon always have water to swim up on their way to the spawning grounds.

Salmon Eggs Have Very Specific Conditions They Can Exist In

Salmon eggs on a
Salmon eggs on a “just right” sized gravel bed. The gravel they are in is small enough for the adult salmon to dig a nest in, but not small enough to coat the eggs and deprive them of oxygen.

Salmon lay their eggs in redds. A redd is simply a little hollow in the gravel bed on a stream bottom that is dug out by the fish. Redds are usually found near the banks of shallow, relatively slow moving sections of stream. The gravel they are in needs to be small enough for the salmon to dig around in (I don’t know of any salmon huge enough to move bowling ball sized rocks around). However, if the particles making up the gravel bed are too small – like silt or clay – then these very fine sediments can settle on the eggs and deprive them of oxygen. It’s sort of a goldilocks scenario: the sediment can’t be too big or too small. It needs to be just right. And this is where wetlands come in.

As mentioned above, wetlands slow down the flow of water. When the water in an incoming stream is moving quickly, the fine sediments are suspended in the water and are unable to settle out. When the water hits the wetland and slows down dramatically,  the fine sediments drift down in the water and settle on the bottom of the wetland. The water keeps slowly moving through the wetland and settling out the fine sediment until it reaches the point where water starts flowing out of the wetland via another stream or creek. The water leaving the wetland is now depleted of the fine sediments that can smother salmon eggs. You can think of the wetland as a giant Brita filter. “Dirty” stream water is poured in top, that water percolates through the filter and the “dirt” is filtered out, then the “clean” water drips out the bottom of the filter. Thus, the “clean,” slower flowing water downstream of wetlands is idea for mature salmon to create redds and lay their eggs.

Wetlands are the Brita filter for fine sediments in streams. Step 1: fine sediment rich stream enters the wetland
Wetlands are the Brita filter for fine sediments in streams. Step 1: fine sediment rich stream enters the wetland “filter.” Step 2: Wetland “filters” out the fine sediment by letting it settle to the bottom. Step 3: Water leaves the wetland “filter” with most of the fine sediments removed.

Salmon Eggs Can Get Washed Away in Water that is Too Fast
The wetlands also act as a buffer to sporadic high flows in the upstream channels. If there is a large rainfall nearby, that can cause the water levels and flow rates in the stream to increase rapidly. These sudden increases can easily sweep away salmonid eggs out of the redds. By having a big old wetland disrupting the stream flow, even large amounts of incoming water from rain can be slowed down enough to not sweep away all the future generations of salmonids.

Baby Salmon Need to Fend for Themselves

Salmon fry are pretty tiny. They need to focus on getting big. Easiest way to get big? Eat a lot and don't move around much. Wetlands let the fry do just that. By the time the fry leave the wetlands, they are several inches long and MUCH stronger and heavier.
Salmon fry are pretty tiny. They need to focus on getting big. Easiest way to get big? Eat a lot and don’t move around much. Wetlands let the fry do just that. By the time the fry leave the wetlands, they’re called smolts and are several inches long and MUCH stronger and heavier.

When the salmonid eggs finally hatch, there are suddenly a ton of baby fish (called fry) that need to survive without any parental help. Initially, they’ll feed on a yolk that remains from their egg, and some insects that inhabit the ecosystem around the low flowing stream they are born in. Once the fry are large enough to swim upstream, they move into the nearby wetlands as a semi-permanent home. Wetlands are the perfect place for the fry to spend their “childhood;” there is very slow-moving water and plentiful food. The combination of these two characteristic allows the young fish to spend their energy looking for food, eating, and getting bigger – not on constantly swimming against the current.

Salmon Must Return to the Ocean Eventually
Salmon actually spend most of their life in the ocean. As the fry mature, their bodies go through “salmon-puberty” and start changing to being able to thrive in saltwater (the ocean) instead of freshwater (the stream and wetland). Once salmon-puberty hits, they need to get to the ocean fast. Their bodies are rapidly changing and making the freshwater streams and wetlands more and more difficult to live in. Luckily, the time it takes for them to mature lines up with the typical massive spring snowmelt. Snowmelt causes a HUGE flux of water into the streams and wetlands, so much that just having some wetlands along the way isn’t enough to buffer it anymore. As a result, stream flow rates increase dramatically and the now adolescent salmon basically ride the current out to the ocean. They continue to grow in the ocean for a variable number of years, then when it’s time to spawn they head back inland and the cycle repeats itself.

Wait a minute. You said in the beginning that beaver dams create wetlands, and that wetlands help salmon spawn successfully.  Wouldn’t building a dam stop the mature salmon from getting up the stream in the first place?
Salmon are pretty amazing in what kinds of obstacle they can get through to reach the spawning ground. They don’t stop to eat once they’ve left the ocean and swim entirely on fat stores (for up to 1000+ miles and 7000 ft of elevation gain). They fight the current 24/7 for months. They avoid being eaten by eagles and grizzly bears. And believe it or not, they jump over beaver dams. Salmon have been shown to jump up to 12 feet vertically to get over obstacles. Beaver dams max out around 9 ft tall, and are usually more on the order of 6 feet in height. Not a problem for salmon.

If salmon can jump up raging waterfalls, like they are doing in this picture, then they can definitely make it over a run of the mill beaver dam.
If salmon can jump up raging waterfalls, like they are doing in this picture, then they can definitely make it over a run of the mill beaver dam.

So there you have it. If you like eating salmon, or just don’t want salmon populations to plummet, then you should care about wetlands – particularly those created by beavers.

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