Perhaps one of the most important things for a wildlife or fisheries manager to understand is the concept of a feedback loop. While this might seem counter-intuitive or a no-brainer type of thing, it is easy to miss things that you don’t think have an impact on a habitat or species, but actually have a significant impact when looked at from a broad scope. I could type and talk forever about this concept, but will keep it brief here. Simply said, feedback loops are just models that help us understand a complex system. Feedback loops help managers make predictions, conceptualize what-if scenarios and look at long time frames. Loops come in a few forms, reinforcing or just positive and stabilizing or just negative.
Our demonstration came the way of a grizzly bear and salmon case study. We formed a loop that included deforestation, clear-cutting, and silt accumulation all the way back to the bears. I knew silt was a problem, but how big of problem I did not visualize until I saw the feedback loop in front of me. The impact of silt on algae is not a minor thing, rather silt all but kills algae; it is not much better for adult or young salmon. The silt buries the algae and detriments growth. Accumulation of the silt limits the areas where female salmon can place eggs. The lack of algae means lack of food for the aquatic insects, and lack of aquatic insects means lack of food for the young salmon. Holy moly!
One of our exercises was to take bears out of the loop. WOW! Bears are so important. Yes, of course you say, but I didn’t realize exactly how many nutrients bears take away from the stream, which in turn enter the soil, which provides more nutrients to white spruce. The heartier the white spruce, the better woody debris the trees produce, which leads to deeper and calmer pools for the young salmon to avoid the current (conserve energy), predators and the pools provide an ideal habitat for the young salmon to obtain food. Moreover, bears also contribute nutrients to the streamside vegetation, and the same cycle occurs which all benefit the young salmon and help these young salmon reach a size large enough where it will enter the ocean and then return, full of nutrients, back to the stream where it first came to life. Then the bears will snag some and the cycle continues. Now think about the aquatic insects, algae, and other items in the stream; those also are in the feedback loop. The system is quite complex and truly fascinating. It really is more than just the bears controlling the salmon numbers. Keystone interaction? Yes indeed.
Just for fun:
I see that OBN has a writing prompt about sustainable fisheries; interesting that this is the topic since we have spent nearly two weeks talking about this in class. I’ll write my post about that this weekend.