The otolith is the fish equivalent of a black box. One warehouse in Bergen contains several million otoliths dating from 1906 to the present day.
Published: 05.10.2020Updated: 27.10.2020Author: Anders Jakobsen
Inside a small room in a big warehouse on an enormous container quay, Sigmund Grønnevik is hard at work.
He is surrounded by tens of thousands of small cardboard boxes, which he is assiduously and systematically putting onto shelves. In the boxes, there are millions of otoliths, which come from the inner ears of fish. Most of them come from cod, haddock and saithe.
In practice, otoliths are “data loggers” which contain lots of information about the life of the fish that they once formed a part of. How old did it get? Which sex was it? What kind of shape was it in?
The oldest of these small, white “stones” is a haddock otolith from 1906.
Saves researchers lots of time
Now information about thousands of fish from the past 114 years is being digitalised. Sigmund’s job is to enter the data from all of the otoliths into a digital library.
“I enter the boat, species, voyage, serial number and survey number. That makes it easier for researchers to find precisely the otolith they are looking for”, he says.
Digitalising the archive also saves the researchers’ time. Lots of time.
“Before, the otoliths were just kept in big cardboard boxes, without really being organised in any way. That meant the researchers had to head down into the cellar or climb up six-level shelving units and physically hunt around for the otolith they needed”, says Sigmund.
Can look back in time
Digitalising the otolith archive is a huge job that requires a high degree of accuracy. That’s because this information plays an important role in helping scientists to understand how fish in Norwegian waters have developed since the start of the 20th century.
“Otoliths are incredibly important” says researcher Jane Aanestad Godiksen.
“What’s so cool about this archive is that it helps us to understand what conditions were like 50 or 100 years ago.”
Vital to fisheries management
Godiksen leads the demersal fish research group, which is completely dependent on otoliths.
“For us, the most important thing otoliths tell us is the age of the fish”, she says.
When the Institute of Marine Research recommends fishing quotas for individual stocks, it is absolutely vital to know the size of the various year-classes.
“To make sure that we harvest fish sustainably, quota recommendations take into account how abundant individual year-classes are. Big year-classes mean higher quotas, whereas small year-classes mean lower quotas. Without otoliths, our current system of age-based management would be impossible”, says Godiksen.
Tell us about temperatures and diet
Otoliths can also answer very many other questions. The “black box” tells us how old the fish was when it reached sexual maturity, and which stock it belonged to.
“Otoliths are rather like tree rings. They consist of calcium carbonate, which doesn’t change over time. So, whatever is incorporated into the otolith at a particular point in time can be studied later”, says Godiksen.
By analysing its otolith, researchers can learn more about what the fish has experienced at different stages of its life.
“Oxygen isotopes give us an idea of the temperatures that the fish was exposed to, while nitrogen tells us about its diet”, says this marine scientist.
Worth their weight in gold in 100 years
Thanks to the archive, researchers can now go back and perform analyses that scientists were unaware of when the otoliths were originally obtained.
But it doesn’t stop there.
“In 100 years, I’m sure they will be able to do things that we haven’t even considered, but which will further improve fisheries management”, says Godiksen.
Stored in old tobacco boxes
When researchers collect otoliths during surveys these days, they are normally placed in identical cardboard boxes, but it wasn’t like that in the old days. Sigmund has found a variety of interesting storage methods.
“We have some otoliths stored in the cardboard packaging for vademecum toothpaste from the 1940s”, he tells us.
“I also find these tobacco boxes and matchboxes fascinating. People reused things very creatively”, says Sigmund, showing us two tobacco boxes branded Petterøe’s and Tiedemanns.
The creative storage solutions probably reflected the need to economise.
“From the year, we know that money was very short. In the 1930s, they sometimes used envelopes. They used whatever they had. There is also a lot of creativity during and just after the war”, says Sigmund.