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Hypoxia occurs when dissolved oxygen levels dip below 2 to 3 milligrams
per liter of water. At such Low Dissolved Oxygen levels, only bacteria can survive for prolonged
periods of time.
Fish species such as the Striped Bass, require at least 5 milligrams per liter of water
in order to live.
Summer die-offs can occurred when a condition referred to as a
"temperature-oxygen squeeze" takes place. During hot weather the water
becomes stratified, or divided into several layers, with the upper layer being
the warmest and highest in oxygen.
Deeper levels are cooler but contain less dissolved oxygen. This will generally
occurs during the latter part of the summer and varies in magnitude from year to
year.
As summer progresses, the upper layer becomes too warm for stripers, which
prefer water less than 78 degrees, and the fish move to deeper and cooler waters
where the best balance of cool temperatures and high levels of oxygen are found.
As the Dissolved oxygen levels in the lower layers are depleted to around two
parts per million, the suitable habitat for the striped bass is reduced, they
become stressed will sometimes quit feeding and eventually die.
In addition, this is a very popular time of the year for striped bass fishing
and mortality is also caused by the additional stress with the fish having been
caught. Stripers caught during this time of the year should not be released.
The duration of a striped bass die off will depend largely on weather conditions
and the period of time it takes for the lake to begin to de-stratify.
Water temperature is one of the most significant factors to rely on when trying
to locate and catch Striped Bass. As water temperature changes throughout the
year, so does fish behavior and metabolism. Learning to identify how lakes
change and how stripers adapt to these changes can improve your success on
any body of water.
Fishing for Striped Bass during the end of the summer months is often
frustrating because warm water temperatures can make finding and catching fish
difficult.
In early fall a precursor to the fall turnover is when upper
water temperature drops into the 75° F range.
Pre-turnover water temperatures instinctively cue fish that winter is coming and
feeding activity increases
What is fall turnover?
It’s a process that breaks down the stratification, or layering, of warm surface
waters above cool or cold deeper waters that occurs in lakes during the summer.
During the summer, mixing only occurs in the uppermost layer of water. Fall
turnover occurs as surface waters cool, become more dense than underlying
layers, and sink, thereby pushing the underlying water layers to the surface.
This mixing action occurs until all water is the same temperature from surface
to bottom.
Fall turnover can be stimulated by wind and wave action. In most
lakes and reservoirs, as water mixes from surface to bottom, it is likely to
become less clear and odorous from gases trapped in the bottom mud. Dark, dead
vegetation is another clue that fall turnover has occurred. This process rarely
lasts more than a week before conditions stabilize.
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