If you have ever been trout fishing, I am sure you have come across a feeder stream that looks super fishy and said to yourself, “I bet there are fish in there!”. If you are anything like me, you file it away in your mental Rolodex of places that are worth a shot. However, those small streams may be important spawning grounds for sub-populations of the fish you are trying to catch!
It turns out that some research on Brook Trout in the Savage River of Maryland (my home water!) suggests that Brook Trout populations may be made up by a number of smaller subpopulations that spawn within particular streams within the watershed.
See:
Kazyak, D. C., Hilderbrand, R. H., King, T. L., Keller, S. R., & Chhatre, V. E. (2016). Hiding in plain sight: A case for cryptic metapopulations in brook trout (Salvelinus fontinalis). PLoS ONE, 11(1), 1–19. http://doi.org/10.1371/journal.pone.0146295
It is easy to imagine a situation where long distances or stream blockages could divide a population of Brook Trout into smaller sub-populations. It is quite striking that Brook Trout, that exist side by side in a section of a stream, may hail from differing populations. Kazyak et al. (2016) (paper listed above) found evidence for a very small amount of interbreeding between Brookies that live in very close proximity. This means that there were two strains/sub-populations living side by side that almost never interbreed!
These findings have all sorts of implications! The one that stands out to me is that the health of a Brook Trout population, or any trout population for that matter, may not be indicative of population numbers alone. Trout production of one stream may hide the lack of reproduction in others. Reductions in spawning habitat and of the gene pool is NEVER a good thing for long-term success. Protecting wild trout is about protecting and maintaining habitat, restoration, of any kind, can NEVER restore what mother nature has created.
Stephen Knott
TheLadyGreyFlyFishing.blogspot.com
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