The scientists used the following formula to calculate the index of diversity (d) of fish.

d = N (N–1) / Σn (n–1)

where N = total number of fish of all species and n = total number of fish of each species

In some years, the values were N = 624 and Σn (n–1) = 64 792

Which years had these values?

Use Figure 8 and the formula above to work out your answer.

Answer ______________

In 1997, the scientists recorded the highest species richness, but the lowest value of d over the 29 years.

Describe and explain how these results for 1997 were possible.

A journalist studied Figure 7 and Figure 8 (on page 16) and concluded that releasing heated water from a power station has no effect on local fish communities.

Use all the information to suggest reasons why the journalist's conclusion might not be valid.