Growth of Dace and Roach in the River Exe Catchment Essay

1443 Words Sep 1st, 2012 6 Pages
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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Looking at figure 9 and 10 there is both the dace and roach both show their slowest growth then any other site, this could indicate that there is a large amount of interspecific completion for food at this site (Cowx, 1989).
The River Calum sampling site has a gradient of 2% which as a fast flow rate that is the 2nd fastest of all the sampling sites. This river also is high in nutrients like the River Creedy due to the runoffs from farm land. With this river there is a covering of fungus for sewage on the substratum, this results in the possible reduce growth of vegetation in the area. With the flow rate been fast and lower vegetation coverage there is a reduced abundance of roach in the area compared to other sites (figure 10). Although the roach are in less abundance they have the longest life expectance along with dace than any other site along the rivers although there are levels of pollution in the water. According to Nunn et al 2007 the reduced growth rates is said to be related to the longer life expectances.
In relation to the overlap of food items when the stomach contents of dace were sampled (Cowx, 1989), show that the main food source was that of Ariel pray, algae and Macrophytes. Whereas roach stomach contents was that of algae, Macrophytes and detritus. This could explain why both species could live long in the area as they predated upon

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