Stewardship Tip July 14th, 2009- Dog Days
The Greeks used the term “dog days” to refer to the days when Sirius, the Dog Star, rose just before the sun. The ancients sacrificed a brown dog at the beginning of the dog days to appease the rage of Sirius, believing that the star was the cause of the hot, sultry weather. Dog days were popularly believed to be an evil time when the seas boiled, wine turned sour, and dogs grew mad.
As summer enters the hot months of July and August, we, in the Northern Hemisphere, are in the middle of our dog days. These days have important consequences for aquatic life.
Oxygen solubility decreases when water temperature increases. Water that is 90° F can only hold 7.4 mg/L diluted oxygen (DO) at saturation; water that is 45° F can hold 11.9 mg/L DO. This physical phenomenon puts a fish in jeopardy; at higher water temperatures, a fish’s metabolic rate and demand for oxygen increases.
It’s not just the warm water temperatures, though. Muggy, overcast, dog days can also deplete dissolved oxygen. During cloudy weather, the intensity of light reaching the water surface is diminished. This can result in a decrease in oxygen production from photosynthesis. Since oxygen consumption remains unchanged, a body of water can have a net loss of oxygen over a 24 hour period.
Whether from increased water temperatures or decreased photosynthesis, lack of dissolved oxygen in water can result in fish kills.
Why it’s important to the fish: As water temperatures rise, the environment for fish becomes precarious. Monitor your favorite fishing hole for signs of oxygen depletion:
Fish swimming at or near the surface gulping air.
Fish suddenly stop feeding.
A rapid change in water color to brown, black or gray, signifying loss of an algal bloom.
A putrid odor arising from the water.
An extended period of hot cloudy weather.
When you see signs such as these, It is best to give the fish a break and set the fishing pole aside. When the dog days set in, it’s time to lay around like a lazy dog.
This week’s sponsor-partner:Tread Lightly
Tread Lightly! Inc. is a national nonprofit organization with a mission to proactively protect recreation access and opportunities in the outdoors through education and stewardship initiatives.
Their partnership makes this week’s Stewardship Tip possible.
Rising demand for our weekly Stewardship Tip and a new partnership with Fly Cast America now makes the Stewardship Tip available in Spanish. Ahora, reciba el Stewardship Tip en español. Gentileza de Fly Cast America.
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