Measuring Ocean Health

On a scale of one to 100, the health of the oceans has been given a 60.

We now have an index of ocean health for coastal waters – both global and national. Published in Nature in August, and the result of a huge amount of analysis by a large number of people, it has received a lot of generally favorable press attention. It is intended to be a measure of sustainability, representing benefits that a healthy ocean can provide to people.

The global index of 60 is the area-weighted average score of 10 goals. A comparable graph has been constructed for each of the 171 countries and associated territories that have any coastline at all (oceanhealthindex.org).

The website associated with the Index is excellent. It lets you explore the scores of each country goal by goal, with some detail on what the scores mean actually mean. It’s worth a visit just to see the graphics. If you want to see all the goals for all the countries on a single table, then you’ll need to go to the supplementary material published with the Nature article.

The index for countries ranges from 36 (Sierra Leone) to 73 (Germany and the Seychelles). For the US it is 63, for Canada 70.

The Seychelles, with the highest index (driversforce.ca)

At first blush, this all seems to make some sort of intuitive sense.

But what does it really mean? Unless we have confidence in the choice of goals and the methods of measuring them, the value of the Index may be very limited.

There are some goals (Natural Products, Carbon Storage and Coastal Protection, for example) that look particularly useful – they are based on reliable data and not too many assumptions, and result in a decent spread in scores.

But in contrast, there are two examples (the Mariculture half of the Food Provision goal, and Tourism) where 90% of the world get scores far too close to zero, while a very few countries get around 100. Both goals are important to include, but they clearly need better ways to measure them. Including them at this stage undermines the validity of the Index.

The scores for Fisheries (the other part of the Food Provision goal) are worrisome for a different reason, for they can be difficult to interpret. Generally the scores are all quite low, which seems reasonable. But here a low score can mean either that overfishing has been extensive, or instead that fish are not being harvested up to sustainable limits.

Both the authors and the reviewers agree that this is a first cut that will be improved as more data are gathered. However, if the scores for a few of the goals are unreliable or ambiguous, then the Index is unreliable. And certainly reducing it all to a single number for the world, or even per country, becomes increasingly meaningless.

But I think there is a greater problem with the Index, one that is fixable.

How can we try to compare Barbados with Japan, or the Seychelles with Germany? We can’t, and we shouldn’t. Yet, if you look at the global distribution of index scores, some obvious patterns pop out. For instance, the countries with the lowest index scores are clustered along west Africa. (Map from oceanhealthindex.org)

If you then look at a global map of the 64 Large Marine Ecosystems that have been identified, covering all of the world’s coasts, those countries all share a single Large marine Ecosystem: the Guinea Current, LME #28. That does make sense – it ties the countries and their coastal problems together in a meaningful way.

The Large Marine Ecosystem: The Guinea Current (lme.noaa.gov)

So why not use the index to assess and compare LME’s instead of countries? We would then, for instance, be able to compare the Caribbean LME with the Mediterranean or any other LME, and not have to break it into many small island pieces, or alternatively have to compare it with the entire coastline of Canada or Russia. Comparisons become far more defensible.

This would encourage countries that share an LME to work together to make it more sustainable. In fact, most have agreed for years that the LME approach is the best way to go. The Index could and should provide strong evidence to support this.

So let’s get this right. The Index has great potential, but not in its current form. Its value is in its details, and in its use in guiding us on how to improve the health of LMEs, not in ranking and scoring individual countries.

The current global score of 60 tells us nothing.

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