Monday, October 27, 2014

They're in the Trees Man!

It's autumn here in the Northern hemisphere, and in the Pacific Northwest many of our salmon species are making their return to the rivers they were born in. This amazing phenomenon has been well documented on TV, but there is an incredibly cool piece to the story that's often missing. One that weaves the ocean, the river, and the land together and shows us that nothing is alone in the environment.

Pacific salmon are a pretty cool group of fish, but honestly it can be really hard to agree on just what the heck a salmon is. This confusion comes from old terms for the same fish doing different things. Ever noticed how salmon and trout look almost exactly the same on the outside? Well that's because they pretty much are. All trout, salmon, char, freshwater whitefish, and graylings are part of the salmonid family. Amazingly many of these fish can spend their entire lives in freshwater, or they can spend part of it in fresh and part out at sea. Fish that have a life cycle which takes them back and forth between salt and fresh water are called anadromous (pronounced an-ad-row-muss) fish. Weirdly enough some species have a freshwater exclusive and an ocean going form, and they get different common names because of it. For example a rainbow trout (Oncorhynchus mykiss) lives in freshwater exclusively, but a steelhead (also Oncorhynchus mykiss) goes from fresh to salt and back again. It's genetically the exact same fish, but because steelhead fill up on tasty ocean plankton they get much bigger and their meat turns a lot pinker.  

"I haven't decided which I want to be yet. I'm taking classes in both and seeing which I like more."
Courtesy Ingrid Taylar via Flickr

Honestly the rest of this post could be about what is and what isn't a salmon, but that can get tedious and there's other things to get excited about this week. In general when people talk about Pacific salmon they're referring to one of five different species, which are all in the genus Oncorhynchus which means hooked nose. These are the coho (O. kisutch), pink (O. gorbuscha), chum (O. keta), chinook (O. tsawytscha), and sockeye (O. nerka). Aside from being many species instead of just one, Pacific salmon differ from Atlantic salmon (Salmo salar) by being terminal spawners. After they reproduce all five of the species listed above die. When I first learned this it seemed so sad and pointless to me. After all Atlantic salmon don't die after spawning, but it turns out the deaths of the adult Pacifics bring enormous amounts of nutrients into inland environments. 

"It's cool birds, I wasn't using my eyes anyway."
Courtesy Lewis Kelly via Flickr

When thousands of salmon flood a stream and die there, their bodies begin to decay in the water, but look at that picture above. Where's the shore? That fish is lying out in the middle of the woods. Even if the shore is just off camera a few feet I guarantee that fish didn't have "walk on land" as part of his bucket list. So how'd he get there? Well the answer is probably a bear. 

Bears are good swimmers, they love the fattiness of salmon, and they don't mind scavenging on rotting food. Bears and other animals drag salmon away from the streams to munch in peace and the parts they don't eat mix into the soil. Then plants in the area pick up those nutrients and use them to grow. One study found that trees without salmon nutrients grew about 2/3rds as fast as those with them. So trees are, through salmon, taking nutrients from the ocean and using them to grow; and there are salmon streams that are as far East as Idaho (That's 450 miles in a straight line from the mouth of the Columbia River.) where oceanic nutrients can be detected in the trees. It's not just the trees either; studies have found oceanic nutrients in the shrubs, ferns, insects, birds, amphibians, fish, and mammals of these environments. 

No wonder we call him the King
Courtesy spappy.joneS via Flickr

The way we know know this is pretty cool too. Scientists use isotope analysis to see how much of a certain type of Nitrogen is inside the trees. You can kind of think of isotopes as sub-species of atoms. They're not all unique enough to warrant calling them something else, but they often behave a little bit differently. Different environments favor the production and preservation of different types of each atom. The ocean, as it happens, is very favorable to the form of Nitrogen that has an extra neutron. So researchers are able to burn samples from the trees and use a cool device called a mass spectrometer to figure out how much of their chemical composition came from the ocean. At one site in Canada they found that in some years up to 80% of the Nitrogen available for Sitka spruce (Picea stichensis) came from those years' salmon runs.

It's become increasingly clear that salmon are important for the health of Pacific forests. And the implication is astonishing. If we want healthy trees, that grow more rapidly, create more diverse habitat, scrub carbon from the atmosphere, and produce more lumber, then we want healthy salmon. Amazing large scale projects with that goal in mind are already happening, and keeping salmon streams healthy is as easy as making sure you pick up after yourself when you visit a river. It may be a long time before we see anything close to historic runs again, but so much is being done on every level of the community that I'm confident we can make a difference.

If that seems hard to believe, remember all of these trees are partly made of fish.
The world is way weirder and cooler than we ever expect it to be.
Courtesy ArkanGL via Flickr


"Family Salmonidae: Salmons and Trouts", The Burke Museum online

Reimchen, Tom, "Salmon nutrients, nitrogen isotopes and coastal forests", Ecoforestry, Fall 2001.

Reimchen et al. "Isotopic Evidence for Enrichment of Salmon-Derived Nutrients in Vegetation, Soil, and Insects in Riparian Zones in Coastal British Columbia.", American Fisheries Society Symposium, XX: 000-000, 2002

Moore, J, & Schindler, D, (2004) "Nutrient export from freshwater ecosystems by anadromous sockeye salmon (Oncorhyunchus nerka) Canadian Journal of Fisheries and Aquatic Sciences, Vol. 61, 2004

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