The E-mail Commentary from Eco-Justice Ministries
The astounding complexity of natural systems gives ample opportunities for delight, wonder and humility to those who are willing and able to look deeply. When we glimpse some of the ways that the multiple parts of a system fit together and interact, we're able to grow in our understanding that the "things" around us are almost never isolated, disconnected things, but are instead members of a dynamic and fragile community.
A report that I read this week provided a jaw-dropping example of the unimagined interconnectedness of God's creation. Not only does this new piece of news stretch our intellect and move us to awe, it provides a vivid warning about the dangers of tampering with the world around us.
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The August, 2006 issue of Scientific American has an article about "The Fish & the Forest." The title sells the story short, though, by not naming a third essential player in the account -- bears. But let's start with the fish.
Many of us are at least vaguely aware of the life cycle of Pacific salmon. Salmon eggs hatch in freshwater streams, and the tiny little fishies go with the flow downhill to reach the ocean. Eventually, the salmon reach the sea and spend anywhere from one to four years swimming in the salt water of the ocean, growing strong and fat. Then, in one of the great wonders of migration, the adult fish leave the ocean and return to same freshwater stream where they were born. There, they spawn, starting the cycle of life once again.
Or some of them do. Not all of the young fish make it to the ocean, and the fish swimming in the sea may fall prey to fishing nets or predation. Only a small percentage of the hatchlings ever begin the journey back upstream to breed.
The amazing new research that I read about this week is concerned with that remnant which makes the return trip to the streams of their birth. In particular, it deals with the large number of fish which get, oh, so close to their goal, but die before they reach the gravel beds where they would lay their eggs. That is where it gets both complicated and fascinating.
Out of the multitudes of salmon swimming upstream, many are caught and killed by bears. The bears -- needing to fatten themselves for months of hibernation -- have voracious appetites, and are remarkably skillful at scooping migrating salmon from the rivers. In the Alaskan streams that were studied, anywhere from 30 to 60 percent of the migrating fish were killed by bears. That's a lot of fish.
Because the bears are such good fishers -- some can routinely snag a fish in less than a minute -- they're not very motivated to eat every bit of the salmon. Indeed, the bears only chow down on the fattiest, most nutritional bits of the fish, and discard the rest.
The bears, though, don't generally drop the chewed up carcass right back into the river. Bears compete among each other for the fish -- even the most successful fishers find that it is easier to steal somebody else's big, fat salmon than to catch their own. To avoid fights over a fish, a bear will leave the stream with its meal and wander a short distance into the forest before taking a few bites of salmon flesh, and then discarding the rest.
This creates a surprising situation where the bodies of thousands of fish are scattered far away from the rushing water of a salmon stream. Many other animals have a field day with this bounteous carrion. More than 50 species of vertebrates including gulls, ravens, eagles, foxes and mink, and also a multitude of insects, feed on the dead fish. The larger of these scavengers will often move the fish even farther from the stream.
What a surprise! Bears eating salmon provide a feast for a diverse collection of animals, some of which never even come close to the water. Those animals, in turn, provide nourishment for an expanding food web. In fact, there are more insect-eating songbirds along streams with salmon, because the dead fish increase the populations of bugs.
But there is still more to this remarkable story.
The salmon which have grown to adulthood in the ocean and fought their way upstream to the spawning grounds carry within themselves high concentrations of important nutrients -- calcium, phosphorus and nitrogen -- as well as fats and proteins which fatten the bears and birds. While we would normally expect minerals and energy to flow downhill, migrating salmon bring food calories and fertilizer uphill in substantial quantities.
In the soils typical of northern forests, plant growth is often limited by nitrogen or phosphorus -- two of the nutrients that are spread into the forests when the bears drop fish away from the stream. The study revealed that up to 70% of the nitrogen in the foliage of streamside shrubs and trees is of salmon origin. The growth of Sitka spruce, a dominant stream-side tree, was three time greater along salmon streams than near streams without salmon. The trees thrive because of fishy fertilizer.
Who could have imagined it? There are healthy forests far from the Pacific because of the key minerals that salmon carry upstream from the sea, and that bears carry to dry land.
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It doesn't take much to break this astonishing cycle. Obviously, if over-fishing or insurmountable dams cut the number of migrating salmon, the escalator of energy and nutrients can't run uphill. If the bear population is reduced, the spawning fish will die in the water, and all of the nutrients will wash back downstream. If deforestation comes right to the edge of the stream (as many clear-cuts do), there won't be a mix of predators to spread the minerals as widely.
Until just a few years ago, no one had any idea about the ways in which migrating salmon carried nutrients from the ocean to the mountains. Dams were built, fishing quotas set, and forest management plans developed without any awareness of the role of fish in maintaining forest health. Now, foresters scatter salmon carcasses near streams that the salmon can't reach, because they've learned how important the fish are to the forest.
This new research opens our eyes to one of the great wonders of this intricately interconnected world. And it should provide a warning to us about inflicting change on natural systems, for we may not know -- and we may never be able to predict -- how the changes we bring will alter complex ecological systems.
Salmon feed the forests! Thanks be to God for this remarkable way of keeping the world in balance. May our sense of wonder help us learn to be very gentle in the ways we disrupt such remarkable systems.
Eco-Justice Ministries * 400 S Williams St, Denver, CO 80209 * Home Page: www.eco-justice.org
Eco-Justice Ministries ended all programming on July 31, 2020. This site is an archive of writings and resources.
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