Truckee River Yacht Club

FISH ECOLOGY--Part II

 The Food Chain or Web: There are four links in the food chain;; all plant life, the consumers of plant life, the foragers that eat the consumers, and the predators that feed on the foragers.  Some species east consumers and some foragers occasionally become predators, therefore, the term  web  is a better description than a  chain .  The sun supplies energy to plants and the plants build their bodies from carbon which they get from carbon dioxide gas and other nutrients which are dissolved in the water.  The abundance of plant life in any given body of water is limited by dissolved nutrients in the water, by the amount of sunlight, by temperature, and other factors.

There is an estimated 10 to 1 reduction of volume through each link in the food chain.  To produce one 10-pound fish, it would take 100 pounds of minnows that ate 1000 pounds of invertebrates that ate 10,000 pounds of plants.  The aquatic ecosystem is a most delicate balance, and anything that affects any link in the chain will automatically affect the build up from producers, consumers and foragers.  Some ecologists refer to the system as a food pyramid rather than a chain or web.  It is precisely this pyramid that severely limits the abundance of predators or gamefish.  In a simplified example, there can only be one 20 pound fish in a lake or river for every 100 2-pound fish available for prey.  The balance of the pyramid will be upset if one of the links were to be varied.

Carrying Capacity: By knowing certain characteristics of a body of water, an ecologist can determine how many fish it can support.  The main concern of those who study ecology of fishes is the condition of the water.  Water quality and conditions not only affect fish directly, but also affects the whole aquatic chain of life leading up to the food fish eat.  There is a very definite ceiling or carrying capacity that limits the pounds of fish (or biomass) as it is known in ecological terminology) any body of water can support in a given period.  This carrying capacity is controlled by ecological base conditions of the body of water.  The ecological base conditions govern the body of water s  biological productivity , or primary food supply.

One limitation on the number of fish that can be crowded into a single lake or pond (or river)is the reaction of fish to each other.  If there are more of a species in a certain lake than the carrying capacity will permit, certain fish excrete chemicals into the water which prevent females from laying eggs.  Abundant spawning stocks of fish often breed poorly and produce the fewest fry.  When populations are high, fewer young will be produced, and when populations are low, more young will be produced.

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