A question was asked: have marlin or swordfish ever been known to attack marine mammals, such as seals or dolphins?
There appears to be only one published scientific observation of interactions between billfish and marine mammals of any kind. This was an observation in 1951 of humpback whales being impaled by (probably) blue marlin off Hawaii.
Two marlin were seen embedded in the flanks of separate whales, which were breaching in obvious stress. The author observed that one of the marlin "thrashed back and forth, snapping off its bill and fell into the water, as the whale turned upright and submerged."
Before going into likely explanations for this amazing observation, there are a couple of important points of which to be aware.
First, marlin do not have teeth, so they could not possibly be trying to eat a whale!
Second, it appears that marlin rarely, if ever, purposely "skewer" their prey. They "bill-whack" their prey, stunning it before they eat it.
On the other hand, marlin and swordfish bills have historically been found embedded in ships' hulls, logs and bales of rubber, and there are also records of marlin and swordfish bills found embedded in three species of marine turtles.
And, to round out this topic, bills are sometimes found in sharks, especially makos. I have personally witnessed several broken off marlin bills, one to four inches, embedded in different parts of other marlin upon weighing.
So, why would marlin and swordfish apparently attack ships, logs or large animals that they can't possibly eat? Are they really trying to inflict mayhem and destruction, or is there another explanation?
We know that many open ocean fishes are strongly attracted to floating objects, the most common of which are tree trunks and logs flushed out to sea after storms.
Predators, especially marlin, are also attracted to flotsam, presumably because of the potential prey concentrated in the area.
A wooden sailing ship, especially one moving slowly, would act as just such a log or FAD (fish aggregating device), so it is highly likely that, in certain circumstances, these ships would be accompanied by a whole entourage of various fish, including lurking billfish.
When marlin attack from below, they often hit with such speed that they propel themselves clear of the water.
Now, if they were to make an error of judgment, just as the intended meal swerved, it is not hard to imagine a crushing collision with the hull of a ship or a log.
This might be where the whale encounters come into play, too. A likely explanation is that the humpback whales were feeding on a concentration of baitfish, and the opportunistic marlin had dashed in for a free feed, and, being so intent on chasing prey, blundered headfirst into the whales.
Marlin attack when they feel the need to destroy things that are in their way. They hit the smallest of things and kill swiftly, sometimes without taking it for food. They are very precise animals that spot things very clearly and deploy themselves with speed. Sometimes they will eat what they are going for, but also seem to kill for the fun of it.
Billfish attacks on whales have been recorded in whaling journals at least as far back as 1832, also noting that no lesser an authority than Jacques Cousteau had written that broadbill swordfish do attack whales out of "irascibility."
Bills were sometimes found in whales when they were being flensed, although we have no way of knowing how common this was.
Billfish are probably quite bad-tempered and they do, indeed, attack whales from time to time.
Back in April 2003, veteran whale researcher and photographer Mark Ferrari was impaled through the right shoulder while filming an injured broadbill swordfish being attacked by a large pod of false killer whales.
The false killer whales were several miles off Olowalu, swimming around an estimated 600-pound swordfish. They kept darting in and taking chunks of meat off the injured billfish, staying away from its bill.
The swordfish suddenly spun around, and without warning, darted toward Mark, ramming its bill through his shoulder. Mark survived the attack without suffering any damage to his shoulder.