SEATTLE — A new study has found that chinook salmon in the Columbia River and the northeastern Pacific from California to western Alaska are not as big as they used to be.

Researchers, in a study published in the journal, Fish and Fisheries, discovered chinook – the biggest and most prized species of salmon in North America – are smaller and younger nowadays.

The big chinook have decreased both in numbers and in size — as much as 10 percent in length, and substantially more in weight, according to data.

In some Alaska populations, big chinook are virtually nonexistent, The Seattle Times reported .

The cause of the overall downward trend in the size of chinook is not well understood, and probably is a result of several factors, the researchers found. But selective fishing for large chinook likely has contributed to the widespread decline of body size, researchers found.

A possible cause is the selective fishing pressure by marine mammals, protected for the last 40 years and surging in population. Seals primarily eat smaller chinook. But killer whales very preferentially choose the biggest.

Scientists from the University of Washington, the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center Conservation Biology Division, and the Alaska Department of Fish and Game examined 85 chinook populations along the West Coast of North America.

Information from: The Seattle Times,