What has nature ever done for us? This is what leading environmentalist Tony Juniper asks in his latest book. He wants us to account for the “ecosystem services” that nature freely provides in order to make our lives possible.
The marine environment offers the vital services that include the 90m tonnes of seafood extracted every year and the role oceans play in keeping the climate stable. But there are other benefits too, which initiatives such as the UK’s National Ecosystem Assessment (NEA) are trying to capture.
Recently, the NEA published an interim report that considered the value of the UK’s marine environment to two important but previously overlooked groups: sea anglers and divers, those aiming to catch or look at marine life just for fun. In the report, they estimate the potential income a large network of proposed Marine Conservation Zones (MCZs) could be worth to these recreational sea-lovers: how valuable is it to protect large areas of the UK’s marine environment from large-scale commercial exploitation? The one-off non-use value of protecting 127 English sites in this network is estimated to be at least £730m to £1.3 billion, with a further annual recreational value for England alone of more than £1.9 billion.
Unfortunately, these numbers do not bear up to scrutiny. That though did not stop them from being picked up in the media, probably because of the prominent press release about it.
Some parts of the report are commendable. The valuations, based on online surveys, are based on standard economic methods and a useful attempt to define the non-monetary value of angling or diving (through things like “sense of place” and “spiritual well-being”). Their results give a reasonable estimate of how the survey respondents value these different sites. Sadly, the extrapolation based on the surveys is not without trouble.
The models used responses from just 273 anglers and 802 divers and then extrapolated those results to the national population of anglers, estimated to be between one and two million, and divers, estimated to be 200,000 respectively. Extrapolating national trends from just two responses per 10,000 anglers and 40 responses per 10,000 divers makes their headline numbers effectively worthless.
This they admit, for the anglers at least, saying that the overall values should be seen as “relative trends, allowing us to distinguish popular from less popular sites, but with considerable uncertainty about exact numbers”. This is disingenuous – if numbers are intended to be relative, then the big numbers in press releases are misleading, and stating this as a caveat, while commendable, will be missed by most casual readers. Stating that there is “uncertainty about exact numbers” also implies they may be underestimates, which I am certain they are not.
Worse than the small sample size is the fact that these samples are self-selected. In a sports club, only a tiny fraction of members do most of the work. These are exactly the same passionate people who will commit to completing a long survey online about their hobby. This is reflected in this survey: about half the angling and a third of the diving respondents averaged a trip almost every week over the last year, a level of commitment higher than the vast majority of occasional divers and holiday anglers.
Treating these tiny samples as random, and then extrapolating to the entire UK angling or diving population puts the number at nearly three million annual visits to English sites by divers and 70m trips by anglers. Compare this with less than two million visitors to the Great Barrier Reef in 2012. (I have critiqued these numbers and the methods in more detail on my blog).
Take Chesil Beach & Stennis Ledges, for example, a site on the Dorset Coast. The estimate of about 2.7m annual sea angling visits will mean many thousand people on the beach every day of the year, which clearly does not happen. Likewise, the authors estimate 26,000 to 44,000 visits a year (70 to 120 per day) by divers to Offshore Brighton, which is well offshore and so would require more than ten dive boats to be operating every single day of the year. Again this does not happen.
This kind of wild, uncritical extrapolation is akin to surveying delegates at the LibDem conference to predict an election landslide. Simple estimates (what does a million visits a year look like?) with some common sense (have you noticed crowds of anglers on Chesil Beach?) and a bit of help from Google (Chesil Beach Visitor Centre receives an average of around 3000 visits per month) can break down such an extrapolation.
Defendants of this approach typically say that putting any value on an ecosystem service is better than putting no value on it, because at least they can then use those figures in the planning process. I have some sympathy with this view, and opening this debate has certainly been useful. But promoting figures that are so clearly wrong – not just uncertain, but greatly overestimated – seems a way to lose credibility among politicians and managers.