Too Hot to Fish?

Jared Reed – Saratoga Lake Steward

 

With the recent heat, many fishermen have been complaining that the water is too warm for the fish to bite. That’s simply not true – fish require food regardless of the temperature, but the water temperature does dictate where fish look for food. Fish are (for the most part) cold blooded, and rely on their surrounding environment to regulate their body temperature, so when the water gets too warm, fish take to the deeper, cooler waters.

While more prevalent in the ocean, and in very deep lakes, shallower lakes can also exhibit dynamic changes in the water column when the air temperature gets warm. In ‘clean’ clear lakes, sunlight can penetrate up to 10 meters (about 30 feet), and this results in the top layer of water becoming very warm. Warm water is also less dense than cold water, which results in a very stratified water column. This ‘layer’ is defined by a ‘thermocline’ (an area with a steep temperature gradient) and a ‘pycnocline’ (an area in a body of water where the density rapidly changes), and in saltwater, there is also a ‘halocline’ which pertains to salinity. This stratification is most prominent in the summer when the air temperature and increased amount of sunlight heat up the water. In the winter the cold air keeps the top layer of water close enough in temperature to the bottom for the thermos- and pycnoclines to be nonexistent.

The different properties of these layers in the water column prevent the water from mixing, and can result in an uneven distribution of nutrients (including oxygen) throughout the waterbody. An extended restriction of oxygen flow can have major implications, such as hypoxia, fish kills, and can be a contributing factor for HABs (harmful algal blooms).

This stratification is naturally occurring, and there’s little that humans can do to prevent it, or undue it. Violent storms and sustained strong winds can disrupt lakes enough to cause temporary relief from the stratification, but the water will quickly settle.

Check out the attached graph to better understand this stratification!
pycnothermocline
For more information, check out:

http://epa.state.il.us/water/conservation/lake-notes/lake-stratification-and-mixing/lake-stratification.pdf
http://www.sciencedirect.com/science/article/pii/S0380133089714799
http://onlinelibrary.wiley.com/doi/10.1029/JC094iC02p02005/full
http://real.mtak.hu/3303/1/1014407.pdf

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