The average rate of change in the dolphin's position can be represented by the quotient of the change in position over the change in time.
The change in position is the difference between the highest point and the lowest point, which is 3.5 meters above the surface and 10 meters below the surface, respectively. This gives us a change in position of 3.5 + 10 = 13.5 meters.
The change in time is given as 12.5 seconds.
The quotient of the change in position over the change in time is then 13.5 meters / 12.5 seconds = 1.08 meters/second.
Therefore, the average rate of change in the dolphin's position is approximately 1.08 meters/second.