By Chris Adams

Luiz Barbieri, a marine fisheries biologist with Florida’s Fish and Wildlife Research Institute, offered National Press Foundation fellows an overview of the tricky science of fish stock assessments. It’s a simple thing, counting fish. Well, almost.

“Counting fish is just like counting trees, except they’re invisible and they keep moving,” he said, recounting an old joke from one of the giants in the field, John Shepherd.

But try scientists do, since having a baseline of the number of red snapper or bluefin tuna or grouper or any number of other species is vital to managing the world’s underwater resources. “Stock assessment” is an important part of that process.

It involves estimating how many fish there are, as well as how many there will be after regulators set catch limits or season lengths. It also means determining what a “sustainable rate” for a particular species might be.

It’s all part of the guiding principle for all fisheries management issues: “prevent overfishing, while also allowing yield.”

“Fisheries stock assessment – its’ not rocket science. It’s harder,” Barbieri said. “You want to know how many are there, and how they respond to fishing.”

He described different data that go into stock assessments, including those derived from commercial or recreational fisheries, as well as those that stem from scientific probes and other research efforts. Researchers take those data and merge it with birth, growth and death rates of a species to come up with an estimate of how many are actually in the water.

That said: It’s all an estimate. And given that people’s livelihoods are dependent on it, the numbers the fish scientists come up with can become the sources of controversy. In fact, what scientists know about a particular species’ numbers is dwarfed by what they don’t know.