Do cod avoid salmon - research still not sure

The Fish Site
by The Fish Site
3 May 2007, at 1:00am

NORWAY - After recent studies, scientists still cannot prove a connection between salmon farming in fjords and the changed behaviour of coastal cod.

The basis for the studies at Fiskeriforskning are allegations that cod which migrates into fjords to spawn, also called migratory coastal cod, has changed its spawning behaviour in fjords that have fish farms.

Early laboratory studies indicated that the coastal cod reacted to the smell of salmon, and it would not remain in water where salmon had been. However, this was followed up by studies in fjords that showed that coastal cod that live in the fjord all year, also called fjord cod, sought out the salmon farms.

New behavioural studies

The research was continued, and behavioural studies of migratory coastal cod have now been done in Øksfjord. Cod swimming into the fjord to spawn were caught and marked with transmitters, and half of them had their olfactory sense blocked. Some of the cod were released back to the catch site, while others were released in inner parts of the fjord, where there are several fish farms.

The studies showed that the cod that were released in outer parts of Øksfjord left the area after less than a week and did not migrate inwards into the fjord. This supports the assumptions that migratory coastal cod spawn in inner parts of the fjord only to a small degree.

The cod that were released in the inner parts of the fjord remained there for three weeks before disappearing from the fjord. While they were inside the fjord, they did not avoid the fish farms. There was no difference in behaviour between the cod with and without the sense of smell.

Consequently, the results are still contradictory, and the scientists believe that long-term field studies are the best solution to document whether salmon farming can affect the spawning behaviour of the migratory coastal cod.