Although largely solitary, humpback whales are sometimes seen in groups. In breeding grounds, females with their calf can be escorted by one or several males. If several males escort a female, there can be competition between males behaving with impressive aggressive behaviour. The mother will travel with her offspring for the first year of the calf's life. Beside this mother-calf relationship, studies have analysed groups that were traveling together and found out there was no obvious relatedness between the individuals either in the same group or in the same day. Either going or leaving the breeding ground, humpbacks seem to not particularly gather with their kin. For example, some associations have been observed for bubble net feeding, probably to help each other to gather as much food as possible. It appears that humpback whale organisation or social structure is not constant nor based on kin selection but formed when needed and based on reciprocal altruism, to help each other out.
Photo by Miquel Pons
In feeding grounds and at least in Faxaflói, humpbacks seem to be solitary, feeding by themselves. However, their songs, their oral communication, can travel extremely large distances. Low frequency sounds can even travel unbelievable distance of hundreds or thousands of kilometres if they are produced at a certain depth in the SOFAR channel where the low frequencies get trapped.
In the bay songs and sounds produced by the humpback might not travel quite that far but still enough for individuals to communicate in the areas of Faxaflói that we usually explore. We have noticed many times that when a humpback was exhibiting active behaviour such as pectoral slapping, tail slapping or breaching, other humpback whales in the bay would "answer" with a similar behaviour.
Photo by Miquel Pons
We took the assumption that when several individuals were seen in the bay the same day or in a 3h range, they might be together, associating. There is no scientific evidence to confirm this but given the acoustic range of these animals we thought it would be interesting to make this hypothesis. One of our research assistants, Hadrien, used his great skills in programming to perform an analysis and visualise which humpback whales were seen together several times in the same time-lapse. When several individuals are seen in the bay in a similar time range (a day or 3h), it might be an association, or they just tolerate to be in the same area. We will call that co-presence.
Groups formed by the analysis are represented by the colourful polygons. They are calculated according to the number of times those individuals have been seen in the bay together in the same day or in a 3h range. Red lines between groups represent intergroup links of individuals that have been observed with humpbacks from another group. Black lines represent intra-group links of co-presence between individuals of the same group. Numbers represent identified humpbacks of our photo-identification catalogue from 2011 to 2021. We have pictures allowing us to identify each one of those individuals and we often give them names.
Humpback whale individuals seen in Faxaflói the same day at least 2 times.
In this first figure we can see that in the 4022 days of sightings of this study, many individuals have been “co-present” in the bay the same day with another humpback whale individual at least two times.
We can also observe that many small groups are formed with individuals that don’t mix with the other groups. There seems to be a large main community of whales sharing the bay and mixing together with a few groups that are socially independent.
Humpback whale individuals seen in Faxaflói in a 3h range at least 2 times.
We obtain the same type of structure when we do the analysis again with a shorter range of 3h. There is still a main “community” of humpbacks mixing together and small exclusive groups, but this time more groups are formed and the main group seem to have less individuals.
Humpback whale individuals seen in Faxaflói on the same day at least 5 times.
In this graph, we asked the program to only show us individuals that have been seen in the bay on the same day for at least 5 times. There are much less individuals in this graph, which shows that most humpbacks do not very often associate with other specific individuals in time and localisation when they are in there feeding ground. This graph shows us seven groups of two to eight individuals. Four of those groups are inter-connected through key individuals that have links with those other groups (individuals 37, 52, 156 known as Picasso, Charlie and Lumière). The other three groups are more exclusive, especially the duo formed by 280 and 220, humpback whales called Kolbrun and Neve.
Humpback whale individuals seen in Faxaflói in a 3h range at least 5 times.
In this graph, we changed the numbers for the names that we gave to the humpbacks in our catalogue and added a picture of the fluke that allowed us to identify them. With only a 3h range for co-presence, less individuals are appearing in the graph. We have five groups, two of which are exclusive duos. Homer Simpson and Mariupol have been seen associating a lot in 2021. The other three small groups seem to be linked, with Picasso and Charlie still being the social individuals linking the groups together as well as Tattoo and Þröstur. Although, 2022 have not been processed in this analysis, many associations were observed during last year.
Most humpback whale individuals seem to not have particularly strong long-term relationships with other members of the population, but a few connected groups seem to appear with key individuals that are particularly social and that are often seen in the bay during the same day or tour. Since the Icelandic population of humpback whales comes from different breeding grounds like the Caribbean or the African west coast, it would be interesting to know if the members of a group are coming from the same or different feeding grounds. There seems to be much more research to do before unveiling the mystery of humpback whale social structure.
By Miquel Pons