ORCAS, FISHERMEN, DEPREDATION AND RECIPROCITY

Text: Sevi Golinvaux, photos: firmm

In July and August, firmm organises 3-hour excursions to observe orcas when they come to catch bluefin tuna from the lines of the fishermen in the Strait of Gibraltar. In this blog we take a closer look at the interactions between orcas and these fishermen.

But first of all: why do killer whales come to take the tuna from fishermen's lines?

Bluefin tuna pass through the strait several times a year, and Iberian orcas remain in the area around the Strait of Gibraltar to hunt their favourite food for a large part of the year. However, tuna hunting is a very energy-intensive activity, as the orcas must dive and chase the fish, which escape at high speed to inaccessible depths.
It is therefore much easier to catch the fish once it is hooked on the line. In this way, the fish cannot escape, which saves the orcas a lot of energy. This behaviour is called depredation.

When I explain this phenomenon in the information talk before our boat trips, I often get the following question: aren't the fishermen frustrated because the orcas are taking their fish?

Perhaps some fishermen are indeed defending ‘their’ catch or trying to keep the orcas away. But perhaps some fishermen feel that what nature offers belongs to everyone and are therefore perfectly OK to help orcas by letting them feed off their lines?

And what kind of thoughts do the orcas have about snitching tuna from fishermen?

I was lucky enough to find a possible answer to these questions when I took part in the “Fifth International Conference on Orcas”. It took place in Tarifa in February 2025, with no fewer than 180 participants from all over the world and a further 80 online. Scientists and experts came from all over the world to present their recent research on killer whales.
A number of topics were covered: health, populations, tagging, captivity, photo-identification, acoustic research, genetic research, the effects of human interaction and orca behaviour. It was a week full of presentations and collaboration between experts and orca lovers.

Regarding our questions about depredation on fishermen, my attention was drawn to a presentation entitled: “Underlying mechanisms, proximate causes, ultimate benefits and implications of why some wild killer whales offer prey to people.” Really? Orcas offer prey to humans? That was news to me.

In his presentation, Jared Towers, a marine biologist from BayCetology in Canada, explains that he has observed killer whales offering their prey to humans. And as no wild animal generally offers its prey to humans, he launched a study to better understand this behaviour. Here's a summary of the findings of his study, which you'll find surprising ...

Firstly, his case study revealed a number of facts:

• 1/The orcas bring the prey towards the boat, release it just in front of the boat, then wait for a reaction before leaving.
• 2/In each case it was an individual killer whale approaching with its prey, but with its pod nearby.
• 3/In 60% of cases, the orca showed no interest in playing; this was not play behaviour, which is very common in killer whales.

Jared then wondered whether orcas simply share their prey because there is an abundance of food? Or is there a “reciprocal” aspect to this behaviour?

So, “reciprocity” in killer whales is a complex psychological behaviour whose aim is to create a bond between individuals, such as helping each other or giving and receiving, and which is thought to increase their chances of survival.
In all populations, killer whales seem to share their prey with their own kind, their family, their clan. In the strait, too, when they capture tuna, we regularly observe them sharing their catch with younger individuals.
They do this because they know they will benefit from sharing. When hunting, for example, some orcas are more active and others more passive, but the prey is shared between them all. Orcas also help each other when certain individuals are ill or injured. There are even exchanges between different groups, such as sharing knowledge and helping each other out in times of need. Orcas are very sociable, as you can see. But that's not all ...

Videolink auf YouTube: youtu.be/BCsgChzbZu8

Another aspect to bear in mind is that, according to scientists, orcas are by nature very curious. They are great explorers. This may be due to the fact that they have a very varied diet, so in order to survive they are always on the lookout for new opportunities. A bit like humans: exploration and learning are skills that increase our ability to survive. There have been numerous observations of orcas learning new hunting techniques.

You've probably already seen videos of a matriarch teaching the younger ones how to catch a seal on the beach...

In conclusion, scientists agree that these orcas share their prey with humans, on the one hand out of curiosity, to try new things, and on the other - incredible as it may seem - to create a bond with us.

As described above, in the world of orcas, socialisation, collaboration and mutual aid are completely natural and frequent behaviours.

Coming back to the Strait of Gibraltar, regarding the question of what orcas think of the depredation of tuna, I've understood that it's perfectly normal for them to come and help themselves to the well-stocked lines. According to their principle of reciprocity, it is natural that the fishermen cooperate with them. Especially as fishermen are catching more and more bluefin tuna and it is becoming increasingly difficult for killer whales to hunt them.

In fact, in his firmm research report 2024, our marine biologist, José Manuel, writes:

The status of the Iberian orcas in the Strait of Gibraltar is “critically endangered”. Although the tuna fishing quota has been increased in recent years, which actually benefits the orcas, the number of boats involved in this activity has also increased, including the number of illegal ones. Added to this are the consequences of the new fishing gear that was recently introduced, the encounters with sailing boats in which some captains resort to vigilante action, the intense shipping traffic ... there are countless threats to the orcas in this part of the planet, hence their worrying conservation status.

So, in order to preserve the Iberian killer whale population, we can hope and encourage that as many fishermen as possible also apply the principle of reciprocity with killer whales and that they share part of their catch with them to help them survive.

And, who knows, perhaps in the name of reciprocity, the orcas will remember and help them too if they find themselves in trouble...