Here are two others. Get a digital camera and morph it with a GPS. When
a photo is taken of the back deck every 5 minutes not only do you have
the date/time on each frame, you also have the lat and long. Put the
unit into a security housing and bolt it to the boat. The guys here
would have a better idea of cost per unit. Maybe $1000 each?

The National Marine Mammal Lab (NMML) people have used satellite
tracking technologies for about 25 years to get diving/movement data of
flippered beasts. Last I heard the units are about the size of a pack
of cigarettes, most likely smaller now. They record depth, duration,
water temp, location etc and when animal surfaces the unit burst dive
data to a satellite, then relayed to your office. Put it on a trawl
door or at the zipper end of the bag. Bruce Mate was the pioneer with
that stuff and worked out of OSU in Newport, OR. I think he's moved
on or retired now. Most likely you have seen his work featured on an
old Discovery Channel program.

Probably the most fun solution to your problem is to go to Seattle, WA
, walk into the NMFS Observer Program debriefing room (Sand Point Bldg.
5) and announce, "free beer for any observer who meets me at
Murphys/Buckeroo/Moon etc. You'll get lots a very bright young people
who'll brain storm you a cheep and fool proof solution for the price
a several pints.

Earlier in this thread you ask if it matters who is gathering the data.
It most certainly does. Also equally important is who will have access
to the data and for what purpose.
Might want ot read a book in the area of social and envionmental
economics. One of the best books I ever read was the history of Cod.
For example, how do you feed Europe when there is no industrial sized
protine source? Yep, 1392 Basks sailed the ocean blue in search of Cod.
In Cod We Trust. Which state flag had a Cod on it? Just another
thought. Why would a colony put a Cod on a coin? How about the more
recent Cod wars of Icland.