Fall Storm Carnage?

Our last posting recognized the Storms of November as notable passings from a human perspective.  What do massive storm events, particularly windy ones, mean for our fish? The Great Lakes provide some interesting examples of how these disruptive forces of nature may be essential to the renewal of fish populations.  The frequent occurrence of windstorms in spring and fall seems to be at odds with the observation that so many of our favorite fishes spawn either in the spring, or in the fall. Strong and persistent winds move millions of tons of water, which, in turn, move mountains of gravel on beaches and shoals of exposed lakeshores. Doesn't this conjure up visions of fish eggs being ground to paste by pounding surf? Perhaps, unless there is some strange convergence between the ecology of gravel bars, and the physics of fish eggs.

Gravel bars provide habitat for many aquatic creatures, including fish such as sculpins, darters, minnows, and troutperch. Insect larvae, crayfish and aquatic amphipods also crawl and swim about the substrate in search of tasty morsels by which  to sustain themselves.  Just as "oats, peas, beans, and barley grow..." into concentrated kernels of nutrition for humans, so too do the reproductive products of birds and fishes provide food resources rich in oil and protein for those organisms prepared to scrape, bite, pierce or suck up these high energy nuggets of nutrition. Unless, of course, these creatures are too busy scurrying amongst or swimming away from gravel or rocks tumbling about in the aquatic equivalent of an earthquake in a brick factory.

Consider also the nature of fish eggs. Many of these are just ever-so-slightly more dense than water. They sink, eventually, into the crevices of rocks and gravel, but their spherical form and turgid resilience assure that the slightest movement of substrate can dislodge or bounce them to a new location. Think how difficult is bobbing for apples in a large tub compared to a small one, or, imagine the difficulty of slicing an inflated basketball with a dull axe, in contrast to hitting a half-inflated ball with the same instrument.

The upshot of these considerations is that the storms of November (or, March) effectively disrupt the physical structure of shoals and gravel bars, just as a moldboard plow or rototiller disrupts the physical structure of soils. This "sets back" the environment to an earlier developmental state from which new organisms can sprout, or hatch, to begin their lives of reorganizing the environment around them to suit themselves.  Ecologists call this process "succession", and it occurs on a variety of time scales ranging from geological time (millions of years), to mere minutes for microorganisms. It can be human-induced as in the farming examples above, or, it may be driven by "natural" processes such as fire succession in forests or prairies, or by windstorms.  It is no wonder then, that the premier spawning time and habitats for whitefishes, lake trout and shallow-water ciscoes in the Great Lakes have been the exposed beaches and shallow reefs of near-shore waters racked by the storms of November.