The Old Man and the Sea: on mating for life

"He remembered the time he had hooked one of a pair of marlin. The male fish always let the female fish feed first and the hooked fish, the female, made a wild, panic-stricken, despairing fight that soon exhausted her..." p. 49 The Old Man and the Sea

I was wondering if what the Old Man caught that one fishing trip with the boy was a blue marlin? According to this website, they are solitary creatures that can sometimes swim in pairs (as he remembered), but they do not seem to mate for life from what I could find online. I wondered why there would be a male/female paired off if they didn't mate for life? Do you know?

In case you were wondering (as I was) which animals DID mate for life, feel free to tilt your head and maybe let an oooooo or ahhhhh escape your lips whilst you peruse this Treehugger article with photos of 11 animals that DO mate for life.