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Hi Simon:
I've used UV lamps, though never underwater--I used them with aquaria
constructed of UV-transparent acrylic plastic. This would in many ways
be the easiest way to pursue your objectives; do they have to be
pursued in the field? You should be able to find an inexpensive "black
light" (high UV output) from a specialty or novelty shop. This, at
least, would allow you to test your VIE, and it'd be fairly easy to
fabricate an underwater housing for a battery-operated lamp.
There are some big problems, however, that you may not have considered.
First and most important many fish species can see UV light, including
juvenile rainbow trout. I'd rather expect juv atlantic salmon to be
similarly sensitive, so UV may disturb them too. The cheap black lights
I refer to above also put out a fair bit of light in the blue/violet
portion of the human-visible spectrum so this may startle the fish even
if they're not UV-sensitive. UV-only filters (to eliminate blue
wavelengths) are very expensive. If you want to pursue these filters,
write to me off-list, and I can help with some sources. Also, UV
scatters very quickly underwater, particularly if there are many fine
suspended particles, so it would be capable of locating a VIE tag only
over a limited distance, dependent on UV intensity, water clarity and
the sensitivity of whatever you're using to detect that fluorescing
tag. Can you work in shallow water, illuminating them from above?
I'd look into using infrared. There are good video cameras that are IR
sensitive, some with an integrated IR source (but check that any
housing won't block either source or in-coming (ie reflected) IR). It's
a fairly safe assumption that your fish are insensitive to IR, and you
could tag your fish with colored acrylic paint (ie blue or red perhaps)
so as to create individually-identifiable marks. (OK that last
suggestion is a little tenuous but easy to try.) This still wouldn't
be easy, but I think it has a bit more promise than the UV
alternative.
I've also tried flash photography at night. As long as you have some
clue about where to point your camera, this can reveal spatial
position, orientation, habitat association, etc with minimal visual
disturbance to your subject...at least until you trigger the flash! I
used a dim red light to orient myself to key features underwater,
pointed my camera, waited two minutes (to mitigate any disturbance I or
my red light may have caused), and released the shutter & flash.
Obviously, I couldn't repeat the procedure at the same location any
time soon, but it worked (more or less) for my purposes.
Good luck. Let us know what you come up with.
Cheers, Pete
----------------------------------
Peter A. Nelson, Ph.D.
Marine Fisheries Advisor
University of California
Sea Grant Extension Program
2 Commercial Str, Suite 4
Eureka, California 95501
tel 707.443.8369
fax 707.445.3901
On May 17, 2005, at 10:27 AM, Simon Blanchet wrote:
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>
> Hello everybody,
>
> I aim to study night activity of atlantic salmon fry in a field
> experiment.
> Because I want to measure activity at the individual level, every fish
> used
> in the experiment will be individually tagged using VIE tags (Visible
> Implant Elastomer, http://www.nmt.us/products/vie/vie.htm). Such tags
> are
> highly visible under low luminosity conditions when fluoresced with
> blue
> light and amber filters.
> However, in a laboratory experiment I found that atlantic salmon fry
> were
> highly disturbed when illuminated with such light. I contacted the
> fabriquant and they said to me that this problem can be resolved using
> UV
> lamps.
>
> I've got two questions:
> -Has someone ever used such kind of UV lamps? Is it really
> possible to fluoresce VIE tags with UV lamps?
> -Where can I find waterproof UV lamps?
>
> Moreover, if someone used to do underwater observation by night, I
> would be
> greatful for any advice!
>
> I look foward to hearing from you
>
> Simon Blanchet
>
>
> BLANCHET Simon
> PhD student
> Université Laval - Québec-Océan / CIRSA
> Pavillon Alexandre-Vachon
> Local 8022
> Québec (Québec), Canada G1K 7P4
> Téléphone : (418) 656-2131 poste 8022
> courriel : [log in to unmask]
>
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