Fish Farming Harms Wild Salmon

[sagefisher]

New Study Details How Ocean Fish Farming Harms Wild Salmon

Farming of fish in ocean cages is fundamentally harmful to wild fish, according to an essay in this week's Conservation Biology.

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," said 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 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.

http://www.cbbulletin.com/310188.aspx


Larry ---sagefisher---

[Hans]

Think this is really a point to worry about Sagefisher.
Despite the fact that most professional net-fishings have been bought by the NorthAtlantic Salmonfund in both Norway and Scotland the amount of spawning fish has become less over the last decade.
It's not only the sea-lice that do all the harm; because seals make holes in the farming-nets, and there are many so called escapees.
Unfortunately these fish seem to be able to find rivers and spawning grounds, thus mixing with the wild salmon.
This causes a breed that is less capable of fighting the dangers they are about to encounter during life at sea.
So most will not be able to return after a few years to produce new offspring.
It's really something to worry about...
Hans

[CoachBob]

The calculations in the paper show that even if lice levels on farm fish are controlled by medication, local wild fish still decline.

This is confusing. Apparently it is possible to control lice through medication. If that is so, why would all the discussion of lice in the preceding paragraphs matter? Is it a question of when the medication is applied and is it only being done after wild fish are infected? If so, why not just apply the medication sooner?

I have no dog in this fight, it just appears that either some of the calculations are SWAGs or it's apples and oranges. If the lice can be controlled, then there are other causes at fault.

[hap]

The lice issue is actually several issues... Slice is the only current lice medication. There are already many indications of resistance developing to the medication. Generally the Slice is given with feed. Not all feed gets eaten and there are many questions about how the Slice will affect other critters. All of which leads to the notion of medicating minimally (saves fish farmers money, too) and carefully... Right on the edge of efficacy.

Planting those pens right in the migration route of the downbound smolts leaves them swimming through an artificially inflated population of lice. The lice are there only because the salmon pens are there. This is not an easy fix...
art

[ak_powder_monkey]

This is not an easy fix...

Sure it is, make salmon Auquaculture illegal, problem solved

[hap]

Easily said, now go convince the Canadians...