Been out of town. This is an interesting thread. Although it is unlikely that a 900 pound halibut is swimming around out there, it is certainly possible.

for you photo measurement junkies, here's a couple formulas:

The head length (tip of snout to end of opercular plate) is about 23-26% of the total length.

To calculate dressed weight of halibut from it's length:
WN = 6.921x10-6 x L3.24 , where WN=(head-off, eviscerated wt in pounds)
and L=(fork length in cm)

Round weight = dressed weight X 1.33

cheers