Describing a graph

This line graph describes the number of common Dolphins seen in Santa Barbara Channel from 1996-2001.
Overall, there was a variation of the number over the period. In 1996, approximately 1500 Dolphins can be seen and one year later, the number reached about 7500. But in 1998, it went down considerably to about 4000. In 1999, It went up to the number of 6000 and decreased again to the number of 4000. In the final year, the number reached about 7000.