Water temperature and fishing 1 macro.

Why is my fishing spot (pool) not so hot after the floods?

Recreational fishermen have for long participated in management and conservation of fish ...specifically because they mostly have a pool they call “my pool”. This could be a stretch of water ranging from 20 meters to 10 kilometres within a reserve or fishing resort, or a specific fishing spot along the banks of a major lake or dam. Now the contrary is also true in that many fishermen (sports fishermen that keep their catch) have totally depleted fish stocks in their pools or fishing spots and even more disturbingly, destroyed the habitat at “their spot” through various malpractices, whether intentionally or unintentionally. 

 However  the “Catch and release” sport fishermen have favourite spots they want to protect because of the productivity at the specific location/s. 99 Percent of anglers don’t study the real reasons as to why their spot is productive; they just ride the wave as long as they can. They don’t normally get it right though for too long as somewhere along the line they will not be able to withstand the pressure to brag about the sizes and or totals and would tell someone that in turn will tell at least 50 others that don’t really have the same ethics, knowledge etc. as the initial “pool owner”. It is the egotistical problem of fishermen..Rarely do you get a fisherman that doesn’t care about the size or totals of the fish he catches. The fly fishing and specimen carp fishing fraternity I think fare the best in this regard.

About our “pools”, let me start by saying that floods cause the water temperature to change and therefore the fish move or migrate or species swop pools or just zones within pools etc. I’m not talking about the initial temperature changes when the water flushes down, following heavy rains but the fact that the habitat has changed dramatically due to heavy rains for long periods that thus causes extended periods of high flows. Exactly like the previous rainy season (summer) in South Africa along the Vaal and Orange River system. In some instances the visibility in the Vaal River was still affected in September due to the Heavy rains in the beginning of 2010. The difference in the “pool” we fished in  October in the Lower Orange River for 12 years have changed so dramatically that I realised that some of us fishermen don’t really understand the complexities of water temperature and the responses of the aquatic organisms to thermal variances caused by this hydrological and structural changes to the habitat as we knew it for years prior to the floods.  Either as a result of nature causes or thermal pollution. Thermal pollution for example occurs at power stations and below impoundments or where irrigation water “runs back”.

It is also the dramatic climatic changes that have wiped out many forms of life on our planet such as the Dinosaurs and others in the past. Just in a smaller scale do radical changes once every 10-50 years change the habitat along rivers. Things then have to “settle” again. Constant even flowing water start carving out pools or filling deeper holes, vegetation increases etc. Let me say categorically that this flooding is only initially bad for fishing, for instance in the season of the flood such as the beginning of this year fishermen rarely got the opportunity to fish. And the beginning of the next spring and summer ( Sept/ Oct) also showed very bad catch records in all fishing aspects. It is however very good for the survival of the fish as the silting up of our rivers due to the down wash of top soil due to bad farming practices etc washed the rivers clean and gravel beds opened up very nicely for fish to spawn in. The Mudfish must have doubled their totals in the Orange river if I gauge it in the duration of the spawn and the prolific flood plains that opened up and had enough water into the September and October months. This in turn will be very good for the Largemouth yellowfish and the Catfish in the Orange River system.

The thermal characteristics of rivers are affected by Hydrological, Regional, climatic and structural influences. 

1-Hydrological influences would be Sources of water, Contribution of groundwater, Rate of flow or discharge, water volume and tributaries.

2-Climatic influences are Air temperatures, solar radiation, Cloud cover, wind speed, vapour, precipitation and evaporation.

3-Structural influences are Topographic features, Aspect and slope, Riparian vegetation, Channel form /morphology, geology, water depth, turbidity and percentage channel as pool.

All organisms have a range of temperatures at which optimal growth, reproduction and general health occurs. Scientists call this the “optimal thermal regime”. Temperatures outside of this range affect metabolism, growth behaviour, food and feeding habits, reproduction and distribution, migration, movement etc. amongst others. 

With the heavy floods that occurred the reeds along the embankment were washed away, trees died due to prolonged periods under water-longer than previous years, sand washed into deep pools, shallow areas are now deep pools, rocks washed open creating exposed rocks and more gravel  and this all had the most profound impact on the water temperatures on the micro level.  The exposed water along the banks that used to be in the shade and thus had cooler water temperatures will have warmer water. The deep pools will now provide the suitable habitat for largemouth yellowfish and large catfish to relax in with warmer water. The water below the rapids that created suitable habitat for yellowfish pre-spawn now was not suitable at all for the pre-spawn at the same time they preferred to spawn during previous years. Deep pools behind large boulders held large fish in previous years with no obstacles but are now unfishable due to large trees and other debris that washed in behind the boulders so more fishing lines break off  after flood years cause anglers cast to normal structures and are familiar with the boundaries of break offs.

So it is my advice that anglers take some time to investigate the habitat or morphology of their waters. Something little fishermen do in any case. A sad case will also be that you could have more drowning as people will venture into known waters that will suddenly be very deep or dive into shallow areas that used to be deep.