Herring fishermen in Nova Scotia are reporting fewer and smaller fish this season. (CBC)

Scientists from the Bedford Institute of Oceanography are on a mission to find out why herring fishermen in Nova Scotia are reporting fewer and smaller fish this season.

The researchers are using sounders and sonars to count the number of herring in an area known as the German Bank, off the southwestern coast of Nova Scotia.

The count may help explain why the catches have been coming up smaller this year.

"When the fishermen don't land fish, people think that there may not be fish," said Gary Melvin, a research scientist. "There can actually be fish. But we want to be sure, one way or the other."

Some fishermen said they believe the catches are smaller because the fish are avoiding warmer water temperatures near the surface and diving deeper, thereby eluding the large nets used to catch them.

"It doesn't mean the stock's in trouble," Melvin said. "It means that they can't catch them."

Melvin said herring population estimates have been made before, but the current research will yield more precise results.

The numbers will be used as a baseline to measure future herring stocks.

Fishermen said the research is a proactive move that will allow them to find out where the fish are going.

"We have to find where that is. Water temperature affects all fisheries, so the more we know about it, the better we can be prepared," said Dick Stewart.

Scientists say the quota for herring has been low in recent years, reflecting both the industry and government's concern about lack of fish.