River Clyde Fisheries Management Trust Ltd.
 

Ecology - (A study of the inter-relations between living organisms and their environment.)

Lochs & Ponds - Originate in various ways depending on how the basins were formed - circular. semi-circular, near rectangular or ox-bow. there are exceptions to these, such as: valley being dammed or waterways.

The interesting point of lakes & ponds from the fisherman's point of view is the depth and what happens during temperature changes; as this affects the salmonids. During the summer months and more so the deeper lakes/ponds can be divided into two layers due to the warming of the top layer by the sun during the calm periods. These layers are thermal stratification, the upper layer of warm water is known as the epilimnion  and the lower colder layer the hypolimnion and the area between the two is the thermoclin.

The graph shows the saturated oxygen at the varying temperatures which will affect the years angling i.e. the high and low temperatures make the salmonids lethargic and are put off feeding. The high temps have a lack of oxygen with the low temperature having an excess of oxygen.
Definitions of large water types - Oligotrophic, Eutrophic, Mesotrophic and Dystrophic.

• Oligotrophic - Usually deep waters, lie on infertile rock e.g. Granite. Poor in dissolved nutrients. These waters are generally found in mountainous areas with most of the lochs in the Scottish Highlands being if this type. Because of the low production of plants and animals oxygen depletion does not occur in the hypolimnion; this where in this cold water environment we will find fish such as the brown trout (Salmo trutta), char (Salvelinus alpinus).
• Eutrophic - These waters lie on a mineral rich rock, such as limestone, and are shallow with a large littoral area rich in flora and fauna. A eutrophic water are usually situated in low-lying farmland. Oxygen may become depleted in the hypolimnion during the summer. Although there maybe trout present within these waters, the conditions are generally not satisfactory for the completion of their life cycle. Fish of the carp family etc. are more prevelant.
• Mesotrophic - This type have characteristics lying somewhere between those of oligotrophic and eutrophic waters.
• Dystrophic - Found mainly in moorland, boggy an mountainous areas. Such waters are rich in organic matter consisting of undecomposed peat and other humic material. The waters are often stained a tea colour and the pH of the water is usually very low. There is very little decomposition because of a calcium deficiency.

Wind effects on large waters -

   Illustration of Langmuir rotations;
open circles=positively buoyant particles,
closed circles=negatively buoyant particles.

In exposed systems, wind can create turbulent, spiral-formed surface currents called Langmuir rotations.
Exactly how these currents become established is still not well understood, but it is evident that it involves some interaction between horizontal surface currents and surface gravity waves. The visible result of these rotations, which can be seen in any lake, are the surface foam lines that run parallel to the wind direction. Positively buoyant particles and small organisms concentrate in the foam line at the surface and negatively buoyant objects are found in the upwelling current between the two rotations. Objects with neutral buoyancy tend to be evenly distributed in the water column. This turbulence circulates nutrients in the water column, making it crucial for many species, however its effect on benthic and profundal organisms minimal is to non-existent. The degree of nutrient circulation is system specific, as it depends upon such factors as wind strength and duration, as well as lake or pool depth and productivity.