Ocean Fish Farming Harms Wild Fish, Study Says

hermanntrude

^^^^^^^^^^^^^^^^^^^
Jun 23, 2006
7,267
118
63
45
Newfoundland!
ScienceDaily (Dec. 16, 2008) — Farming of fish in ocean cages is fundamentally harmful to wild fish, according to an essay in this week's Conservation Biology.


Sea lice on a juvenile pink salmon. Visible are the egg strings on a female louse, and the puncture tracks in the salmon's skin. (Credit: Photo by Alexandra Morton, Raincoast Research)

Using basic physics, Professor Neil Frazer of the Department of Geology and Geophysics at the University of Hawaii at Manoa explains how farm fish cause nearby wild fish to decline. The foundation of his paper is that higher density of fish promotes infection, and infection lowers the fitness of the fish.

For wild fish, lowered fitness means more difficulty finding food and escaping predators, causing higher death rates. But farmed fish are not only fed, they are also protected from predators by their cage, so infected farm fish live on, shedding pathogen into the water. The higher levels of pathogen in the water cause the death rates of wild fish to rise.

The above paradigm explains recently documented declines of wild fish in areas with sea-cage farm fish.

"Sea lice are an important example of disease transfer in ocean fish farming," explains Frazer. "Sea lice are tiny crabs that attach to marine fishes, eating their skin and sometimes deeper tissue. Skin is important to fish because they need to keep their tissues less salty than the ocean. Also, when lice puncture the skin they create an entry point for other infections. So wild fish weakened by lice have more difficulty finding food and escaping predators."

A female sea louse can produce over a thousand larvae during her life. Larvae drift in the ocean and a lucky few of them drift close enough to a fish to attach. Most larvae die without ever finding a fish. In a fish farm environment, a larva's chance of finding a fish increases, so more larvae survive to become lice, and those lice put more larvae into the water. With more larvae in the water, more wild fish become infected and die as a result.

Larger numbers of lice are especially dire for salmon because juvenile salmon must transit coastal areas where salmon farms are located. Juvenile pink and chum salmon (Pacific species) suffer most because they spend much of their early life in coastal waters, and they are so small at ocean-entry that infection by even one or two lice can be fatal.

The calculations in the paper show that even if lice levels on farm fish are controlled by medication, local wild fish still decline. Also, there is a critical stocking level of farmed fish. If a sea-cage system is stocked above the critical level, local wild fish decline to extinction. Long story short — growing farm fish in sea cages can't save wild fish, but it can easily destroy them.
 

Risus

Genius
May 24, 2006
5,373
25
38
Toronto
I'm surprised it took them that long to publish this. It hs been common knowledge for several years... both on the east and west coasts.
 

Twila

Nanah Potato
Mar 26, 2003
14,698
73
48
on the West Coast here, in BC, there is an issue with some individuals in DFO who have a vested interest in the success of farmed fish.

Even though it sounds like a conflict of interest they have invested financial support to those farms. Any negative press would have promptly been followed with a in their pocket scientist stating the opposite.
 

Said1

Hubba Hubba
Apr 18, 2005
5,336
66
48
51
Das Kapital
Apparently it's done much cleaner here, but I'm using shrimp farms as a comparison, which is done differently.
 

Tonington

Hall of Fame Member
Oct 27, 2006
15,441
150
63
If we had the resources that Norway has...the trait for resistance to sea lice is highly heritable (high is any h-score > 0.3) As it turns out, the gains in aquatic species are the same as that of terrestrial species. From one generation to the next, the genetic gains can be anywhere from 10-14%. Further, recent economic analysis places the cost-benefit ratio of efficient breeding programs at 1:15, and currently in Canada the breeding programs might be 2-3% efficient...

So, that's one solution they ought to work on, on top of other gains in breeding. The second is off-shore sites. It's not really feasible right now, the engineers haven't found a way to anchor those off-shore cages sufficiently strong enough, while maintaining economic feasibility.

I think the best near term solution short of closing all of the farms in the archipelago, is to give farm leases in duplicate. The timing of smolt runs is well known. Determining the migration routes, and have the farms out of the way during those runs, like Site B instead of Site A.

I'm going to have to wait for a bit before I can read this new paper, but it's not news by any means. There's quite a few papers on the subject already. This one gets mentioned quite a bit:
Epizootics of wild fish induced by farm fish — PNAS
 

hermanntrude

^^^^^^^^^^^^^^^^^^^
Jun 23, 2006
7,267
118
63
45
Newfoundland!
i figured this wasnt particularly new but i also figured tonington would be interested, and able to tell us what the journalists didnt
 

Tonington

Hall of Fame Member
Oct 27, 2006
15,441
150
63
The notion might not be news, but there's still some uncertainties I'd like to see addressed. How he used physics in this new work might be interesting and novel stuff. Maybe like biological mathematics. Who knows. Thanks for the story Herm.