As I have mentioned on previous related posts visitor numbers should always be measured against ticket price.
Almost all zoos would rather have a million visitors paying £20 than 5 million paying £3
Good point and higher prices seem a reasonable/fair strategy when numbers are steady or rising. However I sometimes get the suspicion that some places try to keep income constant by increasing prices steeply to compensate for falling visitor numbers, a reasonable short-term strategy perhaps but a little dangerous as it has potential to alienate and put off visitors in the longer term (resulting in less overall income regardless of high prices).