Cod isn‘t just cod

“In the final analysis life is first and foremost salt fish but not dreams and fancy,” writes the Nobel Laureate Halldór Laxness in his novel Salka Valka. Cod, flattened and processed in salt is an iconic product for Iceland, characterising life in the manner described by Laxness. The cod is also renowned for having made it into the Icelandic Coat of Arms, and still has a prominent place in the Icelandic national soul:

“Cod is still the most valuable fish caught in Icelandic waters. It is therefore crucial to know and understand its diversity; such knowledge is in fact a prerequisite for sustainable use of the resource,” says Guðrún Marteinsdóttir, Professor of Ichthyology and Fish Ecology. She has researched this important whitefish, a fish that has moulded Icelandic history for ages.

Though most of us think cod is just cod, research in recent years has indicated clearly that the stock structure of cod in Icelandic waters is complex. This is supported by labelling projects by the Marine Research Institute, conducted by Vilhjálmur Þorsteinsson, and a large European project directed by Marteinsdóttir earlier this century.

“Cod by Iceland is made up of a few sub-stocks, each with a specific behavioural and life pattern,” says Marteinsdóttir, to clarify. Most prominent are the so-called deep-water cod and shallow-water cod. Deep water cod stay in feeding areas east and west of Iceland, usually on temperature fronts where northern and southern currents meet. Their feeding behaviour is very special; they constantly swim from the surface down to depths of many hundred metres,” says Marteinsdóttir.

She says that the shallow-water cod stay in shallow waters throughout the year and show no indication of moving vertically. “Both these stocks spawn in the same areas all around the country. The deep-water cod seem to stay a little deeper while spawning.”

Marteinsdóttir says that research indicates that the deep-water cod is characterised by a different physique; i.e. a longer body and larger spaces between fins than the shallow-water cod. “They also have a slower growth rate and become sexually mature later than the other kind,” she says.

According to Marteinsdóttir genetic research indicates that cod with the genetic makeup common among the deep-water cod are steadily decreasing in number due to fishing. This is connected with the growth of territorial waters and advances in fishing technology, and the fact that trawlers have been operating in deeper waters.  

“The next step in this research is to develop a phenotype key to distinguish different sub-stocks of cod. The key will be based on the cod’s appearance as well as the shape of their gills. The method used for the analysis must be cheap and accessible so that the fish may be identified as they are caught, so that classification can be made without having to take samples for analysis on shore.”

This project was launched last autumn; the University works on it with MARICE, the Marine Research Institute, and MATÍS.