Thermal otolith markings Credit: DIPAC

Thermal otolith markings
Credit: DIPAC

Fish Radio

June 2014

 Salmon marking in a new way                          

This is Fish Radio. I’m Stephanie Mangini. How an ear bone can be a salmon’s personal id card. Learn more after this…

 Federal grants are available to help “Made in America” companies compete with imports and save US jobs. Learn more at

 Fish Radio is brought to you by the At-Sea Processors Association – The APA works closely with managers, scientists and environmentalists to protect and preserve our fish resources long into the future. Learn more at


The ear bone of a sockeye, also known as an otolith, is a salmon’s personal identity card. It carries useful information about the fish’s age, growth, life history, and its recruitment. For many years biologists have tracked salmon with Fin clipping, but after a two year experimental process biologists at the Pillar Creek hatchery could be changing that.

 “Starting in 2014 the fish that we take this year all of those fish will be differentially otolith marked. So we won’t be doing fin clipping anymore. All of the fish coming from the Pillar Creek Hatchery as far as late run sockeye go for those projects will be marked with an otolith mark that is assigned by the Department of Fish and Game’s otolith department and tag lab.”

 Al Seale is Hatchery Manager at the Pillar Creek Hatchery in Kodiak.

 “Here at Pillar large amounts of fuel and info structure is invested to differentiate the temperature of the water inside of the incubators to create that mark, but we have run an experimental process the last two years using a dry marking program. “

 The dry markings form when the water level and temperature is changed during incubation of the salmon eggs.

 “We basically drain them dry and cover them with damp burlap. When you drain the water out of the incubator they slowly come up in temperature, then when we turn the water back on the next morning that temperature plunges rather quickly as they are re introduced to the colder water and then that’s what lays down the darker ring on the crystalline structure of the otolith bone.”

 Seale tells how the eggs are growing at a set rate based on the temperature in the incubator. The sudden change in degrees is what marks the ear bone.    

 “When you change that the ring gets lighter, and when you bring them into that cold temperature the crystalline structure condenses and that is what makes the dark ring. We’re trying not to stress the fish anymore than we have to, but we are also taking advantage of the strength of the eggs themselves. ”  

 A few other hatcheries have tried   the otolith marking experiments, but Seale says, he and his team at the Pillar Creek Hatchery are the ones to have pulled it off on a much larger scale.  

Fish Radio is also brought to you by Ocean Beauty Seafoods. Ocean Beauty has contributed over 10 million meals to the U.S. Food Bank network, and is committed to ending hunger in America. In Kodiak I’m Stephanie Mangini.