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,). Y= 3.1439x – 5.1193
R2 = 0.9948
P = 1.02665E-90
From this graph it is can seen that there is a clear correlation between the length and weight of dace Data analysis regression
Table 1. Back calculation of growth: Mean length for age of each group AgeMean Length
Figure 4. The back calculation growth means length of age Fortesque dace.
There is a strong positive correlation between the body size and the fish scales used for ageing the fish
Figure 5. Ford-Walford plot to determine Linf and K
This graph shows the maximum length of infinity of old fish of the Fortesque dace.
Figure 6. Validation graph to test Linf of Fortesque Dace
Table 2. t0 estimation based on each age, and the mean t0 value Fortesque Dace age,
Figure 7. Validation graph to test Linf.
Figure 8. Von Bertalanffy growth curve of Fortesque dace
Figure 9. Length-by-age (mm) of Roach at Exe R. Creedy, Exe Trew’s weir and Culm Stoke Canon. (Data compiled from Ian Cowx’s table of length-by-age)
Figure 10. Length-by-age (mm) of Dace at Exe Fortesque, Exe R. Creedy, Exe Trew’s weir and Culm Stoke Canon (Data compiled from Ian Cowx’s length-by-age table)
From the simultaneous data above there are distinctive variations in the growth of both Leuciscus leuciscus (L.) (Dace), and Rutilus rutilus (Roach). This is not only between given species in any one particular area but also from the different locations within the rivers catchment areas. There are several factors that can contribute to these relationships, this includes abiotic and biotic parameters. The availability of food sources (due to seasonal weather pattererns) and the rivers individual flow rates are major factors that influence the distribution for the individuals from the given species and growth rates. At the Fortesque sampling site which is located at the northern end of the Rive Exe, the gradient of this area has a slope of 2.7%, from all the sampling sites along the river Exe this is the highest. As the gradient is higher the water moves at a rapid flow rate, this elucidates why there is a lack in roach found at this area (see figure 8). From studying the data compiled above, it is evident that dace display their highest growth rate at this location, in addition they achieve the longest length of any other location where they populate along the river. The dace show these traits because they belong to the Cyprinid family which prefer rheophile (fast flowing) and with a high content of dissolved oxygen according to Cowx 1988. Trews weir sampling site is found at the lower regions of the River Exe with a gradient that is much lower than the Fortesque, this results in the water flowing much slower. As this is the opposite environmental conditions the Fortesque site the water flows much slower, this influences the nutrient load of the area resulting in an elevated nutrient load then the Fortesque. The combined pressure of the site having a slow flow rate, and also been sited further downstream then the other three rivers...