Why do cod escape?
Knowledge about why, how and where farmed cod escape is essential for implementing preventative measures.
Just as escaped farmed salmon have caused headaches for the salmon industry, escaped cod will likely become a problem for the cod industry. "Escapes can lead to not only financial losses for producers, but also undesirable effects on the inshore ecosystem," warns Nofima's Pål Arne Bjørn, who led a research project to study escaping cod.
The project is profiled in the most recent newsletter from the HAVBRUK programme ("Nytt fra HAVBRUK" no. 1/2009, available in Norwegian only), whose main topic is cod and escapes.
Individual choices
The first part of the project set out to discover why and how the cod break out of a cage. "We conducted a trial in a tank in which we had made a hole for the fish to escape through," describes Dr Bjørn. "We found that the frequency of escape was highest in the first 60 minutes, and that coastal cod were more likely to escape than Northeast Arctic cod."
"Escaping seems to be a choice of the individual, and it appears that those that have escaped once will likely escape again. We also discovered that cod that had been starved showed a higher tendency to escape compared to those fish that had been fed."
The main findings of the trial were confirmed in a follow-up study conducted at the sea hatchery of the Tromsø Aquaculture Research Station.
Where do they escape to?
The next challenge was to find out where the cod swam after escaping. To get some answers, the researchers released fish tagged with acoustic transmitters in a full-scale, fjord-wide study in Balsfjord in Troms County. Signal receivers recorded the movements of the fish.
"We found that the escaped cod quickly left the immediate vicinity of the cage, and after just a few hours over half of the production cod had disappeared from the site. In the course of four days, nearly all of them were gone," reports Dr Bjørn. It proved relatively easy to catch the escaped fish again, however. In the trial, fully 44 per cent of the tagged cod were caught again with no extraordinary effort.
Must be re-caught quickly
"It is good news that escaped production cod seem to be easier to catch again than escaped salmon," says Dr Bjørn, "but catching them must be done quickly." Nevertheless, he believes that the most critical measures for thwarting escapes will involve technical solutions.
- Published:
- 25.05.2009
- Last updated:
- 27.05.2009
From the newsletter:
The newsletter (in Norwegian):
- Nytt fra HAVBRUK nr 1/2009 (PDF-310.7 KB)
Contact
- Rolf Giskeødegård +47 22 03 70 97 rg@forskningsradet.no
