HABITAT

Habitat refers to the aquatic environment of a particular species. This habitat is governed by such factors as water type and clarity and the availability of food and cover. Anglers often refer to "reading the water" or "reading the structure" of a habitat in order to locate fish. It is a skill that is learned with experience, and subsequent units provide helpful information about how to "read" the environment of a particular species. 

Lake Types

To accurately predict the behavior of a fish we need to classify the aquatic environment. All lakes and rivers are subject to a natural aging process, called eutrophication, taking place over thousands of years. This aging is often quickened by the activities of humans. Agricultural run-off, municipal pollution, and many industrial effluents containing high levels of nitrogen and phosphorus over-fertilize the aquatic environment and age lakes prematurely. There are three types of lakes based on the degree of their eutrophication: oligo-trophic, mesotrophic, and eutrophic.

Although found elsewhere, the oligotrophic lake is the classic lake of the Canadian Shield. Young in geological terms, these lakes are deep (usually in excess of 80 feet), steep-sided with little shallow water and relatively high oxygen levels, and clear. Since they are in the very early stages of eutrophication, they are low in nutrients, restricting weed growth and producing few pounds of fish per acre. The water temperature is organized by thermal stratification; i.e., in summer water is organized into horizontal bands of descending temperature from top to bottom. Within this stratification there may exist a two-storey fish community. The deeper areas are the usual home of the cold-water fishes and the limited warmer, shallower areas may contain cool-water species.

The mesotrophic lake is roughly in the middle of the aging process. Of medium fertility, meso lakes are usually characterized by medium depths, medium oxygen levels, and more gradual sloping shorelines. The water is usually less clear and always warmer than in oligotrophic lakes.

These lakes provide the ideal home for cool-water species. Warm-water fishes, such as largemouth bass, often do quite well in the shallow, warm areas of meso lakes. 

The eutrophic lake is in the late stages of the eutrophication process. These lakes are usually very warm and shallow with very gradual sloping shorelines. Oxygen levels are often quite poor because of the production of carbon dioxide from excessive amounts of rotting algae. Oxygen-producing weeds can do little to help the situation because they do not grow sufficiently, their growth stifled by algae and turbidity which hinder sunlight penetration. Eutrophic lakes are usually the exclusive domain of the stress tolerant warm-water fishes.

A single lake, however, may contain more than one type of aquatic environment. For example, a lake may have an oligotrophic main basin joining many large mesotrophic bays.

Click to Listen!