Counting fish is easy, right? We identify, count and estimate the size of most fish species sighted on each of our routinely surveyed reefs on the Great Barrier Reef. At each permanently marked site, an observer swims along five 50m long marked transects – tallying fishes in a 1m or 5m wide 'belt'. These counts mean we can tell how many kinds of fish are on each site, how numerous they are and what their weight is. Repeating these surveys over and over in the same location reveals patterns about