Could it be near death because it had the bends?
I am thinking because it was hooked on a line,then maybe it had ascended too quickly and couldn't decompress.
My understanding that it's common for creatures from the very deepest regions of the oceans to die when they are brought to or near to the surface. Their entire physiology is based upon living under literally tons of pressure that is the norm at such great depths, and so when that pressure is eliminated their bodies and body systems are unprepared for the radical change. Although I'm no marine biologist and can't cite the specific physiological functions that are affected, I think that these creatures experience just as much of a deadly change as a human or surface-dwelling animal would experience if subjected to the pressures of such depths.
Another example of a very specific physiological design can be seen in the giraffe, whose heart and circulatory system is designed to function only with the animal upright and with the long neck providing a vertical gravity load for the heart and associated organs. When the animal cannot stand up, the gravity load is eliminated and the animal dies.