Sorry I miss that episode, I would have like to have seen their methodology. The efficiency of the swimming motion is not the high in the world of propulsion mainly because it occurs in a liquids as opposed to walking which occurs on a solid and result in a higher efficiency of work done. I know I can pull about 250 lbs. (me on my floattube) on a calm pool of water with a 4 lb. line, the dynamic coefficient of friction is very low less than 0.016. The federal govt. requires a 0.5 coefficient for walking surfaces. All of which really means nothing to most of us.

I would think the highest stress a fish can put on a line is at the end of a jump when even if there is no slack there is a bow in the line that suddenly become taut. Then the fish has hit you with its full weight, dropped at a speed generated from the effects of gravity and the high of the jump. I don't remember many physic formulas and am not inclined to go digging for them at the moment.