I decided to do some reading to fill in some of the gaps in my knowledge
of sea lice, prompted by Tom Wolf's post. What I found out was that all
the "sea lice" are in the same family, and there are a lot of them. The
two main species which affect sea trout are Lepeophtheirus salmonis and
Caligus elongatus. Both of these are limpet like copepods, as Tom
describes them. I'm not sure which species is infesting sea run cutts, but
I suspect it is L. salmonis, it is bigger, more or les the size of the
ones I saw. As soon as I catch another fish I will preserve the lice and
ID them. Nothing I read mentioned cutthroat as a potential host for sea
lice.
Being crustaceans, the lice have planktonic larvae, which metamorphose
into an infective stage (a copepodid). These are the ones which can attach
to the gills, and are presumably too small to be noticed when they are
there. They also can attach to the fins and eyes. The adults can move
around on the body of the fish once they have developed.
The lice feed by scraping away at the mucus and skin of the fish. The
seriousness of this depends on the number of parasites, but can be severe
skin erosion which causes osmoregulatory failure, or opening avenues for
secondary bacterial infection. There is also a high instance of fungal
infection in fish which return to fresh water.
5 L. salmonis or 12-15 C. elongatus were enough to kill salmon smolts. It
took 40-50 C. elongatus to kill adult salmon. The lice also act as vectors
of other diseases, such as Aeromonas salmonicida or infectious salmon
anaemia. (Other parasites can do this too, and many diseases are directly
transmitted in water. The fish in the cages are vaccinated and treated
for disease if it occurs in the pen, wild fish are not so lucky.)
There doesn't seem to be any great seasonality in their occurrance, they
are present all the time. The greatest numbers in most of the studies were
in late summer or autumn. It seems to depend on temperature and salinity
affecting the survival rate.
Fresh water affects different species to different extents. L. salmonis
can live for up to 25 days in fresh water, but C. elongatus dies sooner.
Most of this information came from "Fish diseases and disorders" Edited by
P.T.K. Woo, published by CAB International, ISBN 0 85198 823 7.
With regard to the Irish sea trout problem and gill nets, I don't give any
credence to the theory that the decline was caused by poaching. The
relationship between the pattern of decline and the siting of cages is too
consistent, and the first thing that was noticed was the loss of the
larger sea trout. These were the same size as the wild salmon, but the
salmon didn't decline at the same time, as they would have if there had
been poaching on the scale needed to catch all the sea trout.
There has been a lot of focus on sea lice with little conclusion. Lice are
the most visble disease of course, and others may be more prevalent. I
wasn't aware that lice could transmit ISA. I believe that ISA is what
caused the crash of New Brunswick salmon, and that they have now banned
net pens. More stuff to read up on!.
Anyway, if you got this far, thanks for listening.
N.
On Fri, 13 Jul 2001, Jere Crosby wrote:
> Enjoyed your post and your knowledge on the subjects you wrote about is far
> above mine. I have done a 360 on the subject of net pens. A recent
> article, I believe in Flyfisherman Mag., quoted a Scandinavian source as
> stating, "Any river entering the salt, within 3 miles of net pens, WILL NOT
> have native fish."...the pens are that destructive. They applauded the
> Eastcoast decision to reject net pens. I have learned, as you have stated,
> to take, what fly fisherman suggest as fact, with a grain of salt, until all
> the evidence is in.....to much emotion involved. Jere
>
>
>
>
> ----- Original Message -----
> From: "Tom Wolf" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Friday, July 13, 2001 1:36 AM
> Subject: Re: sea lice
>
>
> > Nicholas,
> >
> > Its been my experience that cutthroat loaded with sea lice mix in with
> those
> > that don't. I see this all over the deep south sound and even up into the
> more
> > open main basin areas. I Believe the sea lice that were supposedly
> responsible
> > for the Irish trout problems (even though the stronger evidence was major
> > poaching with tight mesh nets), attached to the gills of the fish. The sea
> lice
> > in the sound are the limpet like copepods that attach themselves to the
> back of
> > the fish and are found no where near the gills. I have never been able to
> tell
> > while playing a cutt if it was infected with copepods or not until I could
> > clearly see his back. I have not been able to find any good science on
> the
> > subject and do not know what the relationship between host and parasite
> is. I
> > use the copepods as a way of gathering information on the run timing of
> the fish
> > i catch. The diversity of the runs of cutthroat put them spawning up
> rivers as
> > early as november maybe even october all the way through April and May.
> The
> > copepods attach themselves to the cutts once they spend a certain amount
> of time
> > in the salt water so one can conclude that a cutt in Feb. or March covered
> with
> > copepods is either a fish that has wintered over in the salt or an early
> run
> > fish. In any case a cutt need only a bit of fresh water to shake the
> critters.
> > Another gap in the science is that we have no data on the amount of
> copepods
> > before the net pens or after. Then we have to look at the life cycle of
> the
> > copepods and determine when the populations are at their greatest during
> the
> > year and what fish are present at these times. I have followed certain
> pods of
> > cutts over the years and have observed no loss of populations with fish
> that
> > are more prone to infestation than others. A few years back when the
> atlantic
> > salmon escaped from the pens near Bremerton, we had a fishing emergency
> and had
> > to get to the scene right away to test our various patterns on the run
> away
> > fish. I do not recall seeing any limpet like copepods on the atlantics.
> Did
> > anybody else? I can most definitely say there is no correlation between
> the
> > infestation of the sea runs and the proximity of the net pens. There is a
> more
> > dangerous threat to our cutts and salmon in the sound in the form of gill
> nets.
> > The state record sea run is around 6 lbs. How many cutts have you seen
> over 22
> > -24 inches? A four inch mesh will take these beauties out in a hurry. Just
> think
> > what it could be..............
> >
> > The net pens could be a great help to our dwindling salmon runs in the
> Puget
> > Sound. They have the potential to take the load off our remaining wild
> stock (I
> > use the term wild loosely), while still keeping us active and interested
> in our
> > sport. Before we run the salmon farmers out of town, make sure we have
> the best
> > science available to make our case.
> >
> > T Wolf
