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Understanding Thermoclines

Posted by Silverback on 16 October 2007 at 03:55 PM
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The Liquid nature of Water

Refer to the attached MAP to better understand the theory behind thermoclines and their importance to Spearos.

A thermocline is a body of water which has a definite lower temperature than the body of water above it. A thermocline is often more turbid than the water above. Most fish species are poikilothermic (environment determines the creature’s body temperature) and prefer to be in warmer water, warm is relevant based on the area you are in. Certain fish species do prefer the cooler or more turbid conditions in the top of the thermocline e.g. Santer, Red Stumpnose/Miss Lucy.

I make the point that most fish are poikilothermic because some fish are homeothermic, maintain their own body temperature. The notable fish that does this is the Great White, which allows it to hunt from the thermocline. The turbid water provides cover while it looks upward through clearer water for its prey.

Scenario 1 is warm water deeper than 30m. Fish will be spread throughout the area above 30m. Their position would be determined by other requirements e.g. forage, niche habitat etc. The fish are going to be spread far and wide.

Scenario 2 is a thermocline at 15m. Fish will be largely forced upward away from the cold water to a much smaller area. This serves to concentrate the fish in predictable areas specifically the 6 pinnacles all above 15m and the Rocky Foul Area, RFA. The fish in the RFA will behave in a similar fashion to those in scenario 1 but at the pinnacles, fish will be trapped on islands of warm water. There is a proviso. As the thermocline moves in from S-N, the deep area N of RFA may also have warmer water trapped BELOW the thermocline! The thermocline is liquid and as it pushes up and over shallow banks, it may take some time to settle down in deeper water on the other side. The effect is similar to smoke movement in a wind tunnel. In effect this means diving through clear warm water into the colder turbid thermocline. As you continue deeper the water will become clear and warm again, expect fish to be concentrated below the thermocline in these areas. This is time and locale specific.

Remember that because the thermocline is at 15m in one area it does not imply 15m everywhere. On average it would be, but you may find it higher/lower in other areas with significant effects on the distribution of fish in those areas.

What about cold water to the surface? Use a torch to look for lots of fish frozen in caves or stay warm and go to a movie!

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