Essay Growth of Dace and Roach in the River Exe Catchment

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Fish Age and Growth Case Study: Growth of Dace and Roach in the River Exe Catchment
Age 1

Age 5
Age 4
Age 3
Age 2
Age 0

Figure 1 Length frequency histogram of Fortesque Dace.

This figure clear shows that there is a distinctive overlap between the different age groups of the dace from the Fortesque sampling site on the Rive Exe

Figure 2. Observed mean length and 95% confidence limits for dace (Esk).

This figure clearly shows that there is a large difference in length for individuals aged between 2 and 5 years. This indicates that those aged between 2 and 5 grow at a more rapid rate than that of those aged 0 and 1 year.

Figure 3. Log length/Log weight relationship with regression equation. (Fortesque dace,).
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With this type of substratum, it favours idyllic conditions for various types of vegetation to inhabit and create the optimum conditions for roach due to them being both herbivorous and detritivorous feeders (Weatherley, 1987; Brabrand, 1985). Looking at figure 8 this is demonstrated as the Trews weir shows that roach have the fastest growth rate and also attain the largest size than any other site with they are found. From looking at Figure 9 and 10 it is evident that roach find this type of area far more beneficial then dace as roach are in higher abundances at this site. According to a study that had previously taken place by Cowx, 1989 said that dace and roach sampled from the Trews Weir had a significant dietary over lap in this area; figures 9 and 10 also show this.
Data for Trews Weir clearly implies that dace in this area do not have usual food available in this area compared to others along the river so it is essential to look for other food items to populate this region. This explains why they do not have a growth rate that is in line with the other sampling site (figure 9).
The River Creedy’s gradient slope is 1.9% which indicates that the flow rate is at a medium rate. This river also has a high nutrient level as there are runoffs from farm land and with the flow rates not as fast as the Exe then the nutrients as staying within area rather than getting washed away. Dace are found in this area are slightly higher abundances then roach

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