As December quickly approaches, every morning when I head into the Baltic office, I pass a new Christmas tree on display in a shop window or welcoming guests just outside the door of a local bar. After passing a particularly tall pine this morning, I thought about how interesting it is that a tree’s age is not measured by its height, but by the number of rings that are laid down each year in its trunk. This got me thinking – how do the researchers at Oceana determine the age of fish? Obviously, young spawns are smaller than adults, but once a fish is full-grown how you do determine its age?
I did some research on the ICES website and discovered that fish show age remarkably similar to trees. They lay down rings each year in their otoliths – small bones used for balance found on either side of their brains. Under a microscope, the rings can be counted to reveal a fish’s age.
When a fish stock contains a broad range of ages, it is healthy. A lack of young fish could mean poor spawning conditions, while a lack of older fish may signify overfishing.
In the Baltic, a stock that lacks young fish is cod. On average, only two eggs out of 10-15 million spawned by an adult female will develop and survive to maturity. Since 1970, the spawning stock biomass of cod has been in steep decline, and is currently below the lowest recommended level by HELCOM and ICES. Cod are being harvested unsustainably. Off the coast of Demark and Sweden alone, the average annual catch rate is over a 1000 cod an hour.
The European Commission set a legal minimum size requirement of 38 centimeters for cod in the Baltic Sea, in an effort to keep more young cod alive. However, the size limit needs to be increased because a sexually mature female is larger than this minimum length. Cod are being caught legally before they have the chance to reproduce. Also, many fisheries ignore the Commission’s measure and catch undersized cod illegally – as shown in this picture. Oceana is working to eliminate illegal, unreported, and unregulated (IUU) fishing of cod in the Baltic Sea.
Additionally, cod can only spawn in the southern Baltic where the salinity levels are above 10-12 PSU (practical salinity units) and the eggs can float. If the eggs cannot float, they sink to depths where oxygen is too scarce for survival. Cod eggs are vulnerable to environmental changes. If the Baltic experiences an overall decrease in nutrient and oxygen levels, the stock biomass of cod will further decrease. The southern area of the Baltic is where Oceana has recommended new MPAs to be placed, as it is largely unprotected.
Cod stocks in the Grand Banks, near Newfoundland, collapsed due to overfishing about a decade ago – spawning biomass was 90% below normal levels – and are still not fully recovered. Oceana is working to prevent a similar collapse in the Baltic where cod stocks have decreased about 70%.
Like Oceana Europe on Facebook to show your support to end IUU and unsustainable fishing in the Baltic Sea. Regulation concerning this topic is currently under review in the European Commission. Oceana is working with the Commission to protect Atlantic and Pacific salmon, sea trout, and eel in addition to cod.