counting fish tagged posts

In a population of animals or plants, genetic diversity can decline much more quickly than species diversity in response to various stress factors: disease, changes to habitat or climate, and so on. Yet not much is known about fish genetic diversity around the world.

A scientist sent sound waves into the waters of Cabo Pulmo National Park in Mexico, single-handedly surveying the entire 27-square-mile (71 square km) marine reserve twice in just eight days. By shooting sound through the water column in horizontal transects and analyzing how the sound waves behaved, the researcher gathered data that he and his colleagues later used to calculate an estimate of how many fish were swimming in the preserve off the tip of Baja California – and their size.

By doing the same thing in the ocean outside the reserve, the researchers determined that the density of fish was nearly 300 percent higher inside Cabo Pulmo. The fish were also 52 percent larger.

This new application of hydroacoustic technology could lead to much cheaper ways of keeping tabs on ocean lif...