There are numerous methods for estimating the value of different types of ecosystem services. Some methods use observed behaviours to draw inferences about value, but (observed) behaviours are based upon expectations, which can be incorrect. Using data from anglers living in Townsville, adjacent to the Great Barrier Reef (GBR) in a travel-cost model, we show how expectations about the number of fish people believe they will catch on a recreational fishing trip greatly influence estimates of the value of catch reductions (a loss in angler welfare). Experienced fishers have much more accurate expectations about catch than infrequent fishers, highlighting that valuation estimates derived from observable behaviours are most robust when the service being valued is well-known and when people are able to accurately judge the outcome of their behaviours. More broadly, it is clear that under conditions of uncertainty – such as climate change – overly optimistic visions of the future will likely lead us to undervalue (and thus potentially degrade) key ecosystem services – perhaps substantially.

有许多方法可以估算不同类型的生态系统服务的价值。某些方法使用观察到的行为得出关于价值的推论，但是（观察到的）行为是基于期望的，这可能是不正确的。使用旅行成本模型中居住在大堡礁（GBR）附近的汤斯维尔的垂钓者提供的数据，我们显示出对人们相信他们会在休闲捕鱼中捕捞的鱼类数量的期望如何极大地影响对捕捞价值的估计捕捞量的减少（钓鱼者福利的损失）。有经验的渔民对渔获物的期望比不频繁的渔民要准确得多，这突显出，当被评估的服务众所周知并且人们能够准确地判断其行为的结果时，从可观察到的行为得出的估值估计是最可靠的。