I said I would post info on this. Here it is:
I have not read through the whole thing yet but I am sure it will be interesting.
http://publications.gc.ca/collections/collection_2007/dfo-mpo/Fs97-4-2662E.pdfThe potential for predation by caged Atlantic salmon on wild food organisms has
raised concerns about the possible impacts on local populations of wild fish species in
the vicinity of fish farms. The use of
bright lights on some sites had raised specific
concerns that wild species of fish and zooplankton were being attracted to the lights and
were then being consumed by the captive salmon. We collected and examined
stomachs from Atlantic salmon reared at four different aquaculture sites on the northern
end of Vancouver Island. One site used large lights as a technique to enhance growth.
We examined a total of 600 stomachs from all sites collected over a 9-week period. We
collected another 134 stomachs from an experimental aquaculture site near the Pacific
Biological Station, Nanaimo. Most gut contents were contained within caecae, in
various states of digestion. The gut contents varied in time and within and among pens
but very little wild feed was taken by salmon at any of the sites. The main wild
organisms consumed were caprellids, small crustaceans that are part of the ‘fouling’
community that grows on the webbing of nets on the cages where the fish are held.
There were some wild pelagic organisms such as copepods and euphausiids but these
were rare. Only one fish was found in the stomachs, a small sand lance (Ammodytes
hexapterus). No fish larvae were found in the stomachs but very small items, such as
larvae of marine fish such as herring (Clupea pallasi) or eulachons (Thaleichthys
pacificus) might have gone undetected because after a short time in the stomachs, the
fragile tissue in fish larvae would have been unrecognizable. It is probable, however,
that if substantial numbers of fish larvae had been consumed, we would have detected
some. There were no obvious differences in the consumption of wild organisms among
the sites and lights had no apparent effect on the consumption of wild food.
http://publications.gc.ca/collections/collection_2007/dfo-mpo/Fs97-4-2662E.pdf