Age Of Cockles Lab Report

Using the Von Bertalanffy equation, the size and age of cockles in different intertidal locations could be compared. This was achieved by firstly, measuring the length of each cockle from the three intertidal positions (high, mid, low) from the anterior to the posterior of the cockle using a pair of calipers. This length was recorded on an Excel spreadsheet in millimetres (mm). Each cockle was also placed under a dissecting microscope where it’s winter rings were counted to determine the cockle’s ages (years) if no rings were present the cockle’s age was recorded as 0.5 years. This data was then sorted based on age for each tidal zone. To find the average length for each age in each shore height, the formula “=AVERAGE” and the data range was selected, giving an average length for each age.
To do this a scatter plot using the average data previously created was produced, with growth rate (L/T) on the y axis and average length at age (L(t)) on the x axis. A trend line and an equation of the line were added to the graph to show the relationship. Using the equation “y=mx+c” we estimated “k” by using the negative gradient of the line to produce a positive “k” that was entered into the “L” (Table 1) for each shore height. To find the estimated “L” the equation “y=mx+c” was again solved where y=0 and the results placed in the same table as the “k” results. To calculate the expected mean length at age the Von Bertalanffy equation was used. The formula in excel was entered in the following format: