"Nytt fra HAVBRUK" newsletter no. 2/2009:
Farmed cod gone astray
Researchers have now documented what many have feared: not only do farmed cod spawn in their cages, but the larvae journey far and wide. And some survive to become sexually mature.
Experts have long warned against the dangers of interbreeding between production cod and wild coastal cod, but documentation of the occurrence of interbreeding has been lacking. Furthermore, greater focus has been placed on fish escapes rather than on what happens to any eggs from cod spawning in their cages.
Viable larvae
"It was not even known whether the cod actually spawned in their cages, and if so whether the eggs would be fertilised, and whether those would survive," says researcher Knut Jørstad of the Institute of Marine Research, who is leading the group that has answered these questions. The project is profiled in the most recent newsletter from the HAVBRUK programme ("Nytt fra HAVBRUK" no. 2/2009, available in Norwegian only). This issue of the newsletter is focused on sustainability.
Looking for offspring from genetically marked cod. (Photo: Skjalg Ekeland)
"With this study, we have been able to verify that cod do indeed spawn in cages, that the eggs survive and that the larvae journey far from the production sites. What's more, our current investigations indicate that a large proportion of the larvae survive into adulthood. We have captured sexually mature cod that were the result of a 2006 trial involving in-cage spawning."
Genetically marked cod
This study was made possible by a strain of genetically marked cod that were bred at the Austevoll Aquaculture Research Station from 2003 to 2006. These cod originated from the 1990s and possess an extremely rare gene that can be easily identified in larvae and adult cod.
"In the first trial, in 2006, we placed a small number of these marked cod into cages at Heimarkspollen, a small fjord in Austevoll municipality. We were able to document that they spawned and that the larvae travelled far from the cages. The following year we scaled up the trial and placed 3,000 cod ready to spawn.
"That trial confirmed the first year's findings," continues Dr Jørstad. "In the area surrounding the cages we found that about 35 per cent of the larvae were from spawning in the cages. They had spread out across a large area, even beyond the Heimarkspollen fjord."
Needle in a haystack
The next question was whether the larvae would survive or end up as food for other fish.
"The fieldwork we are conducting now involves capturing cod to check if any of them carry the marker gene. We are searching for cod between 35 and 40 centimetres, from the 2006 crop. To ascertain anything with any certainty about the survivability of our marked cod, we need to capture a large number of fish. It's a bit like looking for a needle in a haystack," explains Dr Jørstad.
The fieldwork, led by Terje van der Meeren of the Austevoll Aquaculture Research Station, is still underway. Preliminary findings, however, indicate that 4-6 per cent of the targeted-sized fish captured carry the genetic marker.
"This is a surprisingly high proportion," says Dr Jørstad, "considering that these are cod from the first release in 2006. So we anticipate a substantially higher ratio next year, when the 2007 crop has grown large."
Do they interbreed?
The remaining question, nevertheless, is whether farmed cod interbreed with wild cod.
"We have not yet analysed all the material from this year's spawning season. But we cannot expect a definitive answer until 2010 or 2011, when the 2007 year class reaches sexual maturity." Dr Jørstad is anxious to find out, yet he fears the trials will confirm the worst.
"Interbreeding could represent a serious threat to wild cod. At the same time, it could threaten the aquaculture industry, since biological diversity is required in order to selectively breed new generations of hardy, healthy production cod."
- Published:
- 27.08.2009
- Last updated:
- 27.08.2009
Other articles from "Nytt fra HAVBRUK" no. 2/2009
The newsletter (in Norwegian)
- Nytt fra HAVBRUK nr 2/2009 (PDF-336.2 KB)
Contact
- Rolf Giskeødegård +47 22 03 70 97 rg@forskningsradet.no
