This episode of More or Less was broadcast on Thursday, 19 June, 2003 on BBC Radio 4 at 15:00 BST.

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The seas are empty almost to the point where fish stocks cannot replace themselves, if you believe the scientists.

There is still a viable industry, if you believe the fishermen.

Whether that industry is allowed to continue depends on counting those fish.

So who does it, how do they do it, and are they accurate?

In freshwater, the quantity of fish in a lake is used to measure the health of the local environment.

Here too, we need a way of counting things we can't see, in places so vast we may not know what we have missed.

Fish won't form an orderly queue at a census point, yet crucial judgements hang on an accurate count.

More or Less investigated, discovering, among other things, the importance to the count of seal poo.

Plus, do we really know the risks of cancer?

We asked if the way we use the numbers causes undue alarm and wasteful research.

Producer: Michael Blastland
Editor: Nicola Meyrick