I may be painting myself into the salmon-blogger corner here at Nature’s Confluence, but quite simply, I think they are fascinating, and they give us so much to ponder! So I hope others enjoy reading as much as I enjoy writing about this astounding fish. This post moves away from direct management concerns in California and talks a bit more about the big evolutionary picture of the salmon life-cycle. Spoiler alert - there are no answers here, just some ideas and lots of questions waiting to be answered.
What could possibly inspire a juvenile salmon shorter than your toothbrush to swim hundreds or thousands of miles from their home stream to the vast ocean? There are actually many analogous migrations throughout the animal world, including those of birds, butterflies, and caribou. The study of these risky, long-distance movements has resulted in theory about evolutionary ecology and the selective pressures that result in these seemingly improbable behaviors.
What is a sensitive species? A dictionary definition of sensitive is “quick to detect or respond to slight changes, signals, or influences.” According to Merriam-Webster, the definition of tolerant/tolerance is “the ability to accept, endure, experience, or survive something harmful or unpleasant”. So what makes a species or group of species such as amphibians, which are now currently considered “sensitive”, actually sensitive? Amphibians are listed as sensitive in many documents, for example, the US Forest Service defines sensitive species as “species that need special management to maintain and improve their status on National Forests and Grasslands, and prevent a need to list them under the Endangered Species Act (ESA)”. But the question should be, what are these organisms “sensitive” to? Amphibians have been around a long time (hundreds of millions of years!) and are surprisingly tolerant and resilient; some species of amphibians can freeze solid!
To really get a sense of this, let’s talk about extremes. Amphibians were of particular interest to early physiologists because of their unusual respiratory and metabolic adaptations. This led to some rather remarkable experiments. For example to determine if respiration could occur via the skin, physiologist W. F. Edwards removed lungs from frogs and found they could survive in cold water saturated with air for over a month (Edwards 1824). In another experiment a geologist (William Buckland) encased toads in sandstone and limestone chambers and buried them for a year to see how long they would survive*. Those in the more porous limestone survived the first year; the others did not (Buckland 1832). Other experiments involved coating frogs in paint or oil to see how it affected respiration (Edwards 1824, Wells 2007). We now have a better understanding of many amphibian adaptations, including their very low metabolism, and the ability to respire and hydrate through their skin, which makes them both resilient and sensitive (according to the dictionary definition) in a wide range of environments.
Macabre examples aside, the point is amphibians possess amazing adaptations that make them quite hardy organisms. We tend to think of them as “sensitive” without understanding they represent 360 million years of successful adaptation. Diversifying around the Devonian extinction event, amphibians successfully weathered the next three major global extinction events (ending the Permian, Triassic and Cretaceous). They are finely tuned to the ecosystems in which they persist, often with amazing resilience to very dynamic environments; from deserts to tropical rainforests to artic conditions where they can freeze solid (I am certainly sensitive to freezing solid). This close link means amphibians are both sensitive and tolerant to changes in their environment (according to the dictionary definition).
Just as a deck of cards has four different kings, the state of California has four different types of King Salmon. Each run is creatively named for the season when the adults return to the rivers – we have fall, late-fall, winter, and spring runs. King salmon, also known as Chinook salmon, are the topic of recent news in major California newspapers and science publications alike. One type of Chinook salmon, the winter-run Chinook, is only found in Northern California and is now staring extinction in the face. So I thought I’d take a few paragraphs to introduce you to this fascinating critter, and try to explain why this fish, which requires cold water during California’s hot summer, exists here in the first place.
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