You may not have thought about this before, but a fish is basically a miniature submarine. That is, every fish has a recognizably distinctive shape and acoustic signature.

This fact has tremendous practical importance. Because fish resemble submarines, the acoustic and optic technologies that we developed to track submarines during the Cold War can now be used to count the fish in the ocean.

"Why," you might reasonably wonder, "would anyone want to count the fish in the ocean?"

Jesse Ausubel, Program Director for the Alfred P. Sloan Foundation and one of the forces behind the worldwide Census of Marine Life, has several answers. The most obvious is that we need to understand what’s there if we are to protect it.

This includes helping prevent the further collapse of our fisheries. Dozens of fisheries, such as New England's cod and haddock industries, are no longer commercially viable because of overfishing.

Fish are a critically important food source that we need to protect. People consume 80 million tons of fish taken wild from the sea annually. That compares with 50 million tons of beef that we consume world wide.

Fish may be important for as a food source, but there’s an even more critical reason for wanting a better understanding of fish numbers. According to Ausubel, knowing more about the abundance and distribution of fishes would improve our understanding of the ocean's "biological pump."

This is the mechanism which transfers carbon from the atmosphere into the deep ocean. By removing carbon dioxide from the atmosphere, the "biological pump" lowers the concentrations of one of the main green house gases in the atmosphere.

The more we know about how what marine life is there and what role it plays in the earth’s eco-system, the better chance we have of foreseeing and dealing with threats to the ecosystem. This knowledge can affect our survival.

We can probably agree that having a census of fish is important, but don’t we already have a pretty good idea from the records that fishermen keep of their catches?

Also, counting the fish caught in nets can be quite inaccurate, especially for the smaller species. On top of that, there are vast areas of the ocean which aren’t fished, so we know almost nothing of the life forms there.

If the existing ways of counting fish are inadequate, how do Ausubel and his many colleagues propose to get an accurate census? One of their most exciting techniques involves that nice coincidence about fish resembling miniature submarines.

The same technologies that were developed for keeping track of submarines are now being used to recognize different species of fish. With modern computers, scientists can actually count each fish in a school.

Today, for the first time, we’re able to make accurate and representative counts of marine life from all parts of the ocean. Ausubel estimates that the Census of Marine Life will take 10 years and will cost $1 billion.

So far, fifteen countries are working on it along with sixty different scientific institutions. Their work is so important that it could affect not only our food supply, but the future health of the planet.