Tourists and crew on a whale-watching expedition from Bremer Bay were distressed to see a humpback whale with a fluke tangled in fishing gear. When they saw killer whales heading towards it, they feared the humpback's day was done, a suspicion the unfortunate whale probably shared. Yet instead of living up to their names, the orca pulled most of the fishing lines off the humpback and then swam away, leaving the amazed observers wondering if their actions were deliberate cetacean solidarity or simply chance.

Humpback whales are rarely seen in the summer months in the waters off southern Australia, where Whale Watch Western Australia (WWWA) operates. However, WWWA owner Gemma Sharp told IFLScience that during their migrations, they sometimes fall prey to orca pods.

Orca tackling a healthy adult would likely be crushed by a blow from the tail. However, Sharp said; “Half the pod will distract the mother so the other half can drown a calf a few hours or days old.” Once a juvenile humpback leaves its mother, the danger returns, with pods sometimes grabbing the larger whale's flukes and trying to roll it onto its back and keep it there long enough to drown.

Having witnessed a humpback barely survive such an event last year, the WWWA crew feared the tangled individual would prove a sitting duck for the orcas, who they know well enough to have individually named. They launched a drone to gain footage of the terrible event, but instead got something much better.

“We could see Blade swimming directly underneath his fluke and looking at the rope entanglement,” WWWA report on their website. “Further Orca arrived in the area and similar approaches were made as they charged towards the humpback while he defended himself with pectoral fins and fluke swiping. Matriarch Queen arrived and moved towards the Humpback Whale which caused a commotion of white water and then something incredible happened… a large chunk of the green rope that was entangling this Humpback floated free behind him.”

Nor was the pod simply giving the humpback a fighting chance; they headed west, while the freed whale approached the boat before wisely swimming east.

On the humpback's approach, the WWWA team was able to see only a little fishing line, probably not enough to pose a major problem, was left. On the other hand, the whale was badly underweight and riddled with parasites, indicating he had been carrying the line for a long time and had struggled to feed. Presumably, this was why he wasn't in Antarctic waters in search of summer krill like the rest of his kind. The events occurred off Bremer Bay, where ghost currents produce an astonishingly rich marine ecosystem.

Sharp told IFLScience that orca pull the skin off beaked whales – along with squid, the main summer diet for this pod – before they eat them, which is thought to be an effort to avoid the parasites. Perhaps the whale lice plaguing the humpback saved him from a worse fate.

That still leaves the question of why the orca helped their usual prey – Sharp said some customers joked they were leaving him to fatten up for next year. Alternatively, the orca may have simply been curious about the fishing line and dislodged it by accident while investigating. Sharp notes killer whales have been known to bite expensive satellite tags off larger whales.

However, the unusual way the orca moved left Sharp with the distinct impression they “Felt like giving the humpback a second chance.” She notes they sometimes bring gifts such as sunfish to the boat, despite not being fed in return. Perhaps this really was an example of that much-debated thing, altruism in animals.