Enough of this love for marine arthropods in which we’ve been indulging over recent weeks! New Scientist sets us straight with their revelations over a growing menace of parasitic proportions. Or, at least, of parasites – big ones. Creatures called sea lice are on the march:
Fish parasites from salmon farms on the west coast of Canada are driving the local wild salmon to extinction. The wild fish could be gone in four years, warn scientists in a new study, unless the farms are moved, or made watertight.
Critics of aquaculture have long charged that salmon farms harm wild fish, but this has never before been demonstrated so dramatically.
…Tiny shrimp-like parasites called sea lice can infest the skin of adult salmon and can kill thin-skinned juvenile salmon. However, juveniles rarely encounter lice naturally as the parasites normally stay out at sea with adult fish, while the juveniles hug the coast as they migrate from their native streams into saltwater.
But salmon farms in coastal waters swarm with sea lice,exposing juvenile fish.
NB: These sea lice are completely different from the sea lice I grew up dreading on the Florida coast near the Gulf Stream.
The paper you reference, Krkosek et al, specifically make a point that the “prediction” is “if things don’t change”. By its very nature, the environment is an ever changing entity. We cannot predict what will or will not happen based on models.
Additionally, the same paper omits earlier data that does not support their model. They have selectively utilized data sets that they can manipulate to their benefit to support their argument.
Further, sea lice are very much present in the near-shore environment. To portray them as existing out int he open ocean until farms came along is simply untrue. Salmon migrating out from streams and rivers have had to cope with sea lice since before humans roamed the earth, and they will have to cope with them long after we are gone…assuming the commercial fishery and our own pollution doesn’t wipe everything out first.
Fish on salmon farms acquire lice from the environment and from passing wild farms. In turn, assuming farms are not treated, they “can” act as an amplifier of parasites, that is certainly true.
However, bear in mind that it has always been normal for up to 97% of all the pink salmon migrating out of a stream to fail to return due to natural death by disease, parasites, predation etc. A normal, expected return (escapement) is in the range of 3-5%. That’s normal!
One other cool fact, we are so busy comparing everything that happens in BC to the lice problems in Norway. We base our expectations on what has happened there. But there is evidence that the lice we have here are at least 10% different in their genetic make-up when compared with those in the Atlantic. Chimps and humans are closer…species are defined by differences in the 3% range.
The truth is, we simply don’t have the data to say much of anything about sea lice and pink or chum salmon in BC because we only just started looking at them to see if there really is anything unusual going on…or if natural bumps in the environment (water temperature, salinity etc) have caused some of the blips we have seen. Is aquaculture a culprit? Maybe…but maybe not. Each argument bears consideration……
Apologies, in paragraph 4 I meant to say wild fish not “wild farms”