More than 100 eagle rays gathered around a tuna farm off Malta; scientists say it is the largest aggregation of the species ever recorded |

Picture of Myliobatis aquila. Image Credit: Wikipedia

More than 100 ‘eagle rays’ were recorded gathering around a tuna ranch off the north-eastern coast of Malta. Scientists believe it is the largest aggregation of the species ever recorded. The remarkable sighting was captured during routine underwater monitoring in October 2024, when a remotely operated vehicle surveyed the seabed beneath several tuna cages. Researchers estimated that between 100-150 rays were present, moving through the water and across the seabed where leftover food fish had accumulated. The study, published in the journal ‘Marine Biodiversity,’ suggests that this gathering was largely driven by the opportunity to feed on this readily available food. Common eagle ray aggregations are rarely documented, making the discovery particularly significant. The researchers also noted that the species is considered vulnerable in the Mediterranean, raising important questions about how tuna farming may influence the behaviour and conservation of these rays.

How the 100 eagle rays were recorded gathering around the Malta tuna farm

The discovery was made during routine monitoring of the seabed near tuna ranches off Malta. According to the study, researchers surveyed 8 of the 24 tuna cages on the site, along with 4 nearby reference locations. A remotely operated vehicle(ROV), collected video footage at depths of around 50-55 metres. Out of the eight cages surveyed, three had fresh food fish resting on the seabed beneath them.The largest gathering of common eagle rays (Myliobatis aquila), was found around one of these cages. Their constant movement made an exact count difficult, but researchers estimated from the footage that between 100-150 individuals were present. Smaller numbers of other rays, including common stingrays, were also observed. However, this gathering of eagle rays was not like any previously documented for the species. Earlier reports have described much smaller groups, and the researchers believe this Malta sighting is the largest recorded aggregation of common eagle rays till date.

Approximately 30 common eagle rays are visible in this image, some of which are feeding on the food fish that have settled to the bottom. Image Credit: Springer Nature

Leftover fish created a rare feeding opportunity for the eagle rays

The footage provided a strong clue about what had brought so many rays together. The large aggregations were observed only beneath cages where food fish used to feed the tuna had accumulated on the seabed. Under the remaining cages, where no food fish were present, researchers recorded only isolated rays. The ROV also captured the eagle rays actively feeding on the fish. They frequently bumped into one another while moving around the seabed, and two individuals were seen tugging at the same piece of food. The researchers said these direct observations provide strong evidence that scavenging on leftover fish was a major reason for the aggregation. The study noted that previous observations of common eagle ray gatherings had rarely provided such clear evidence about why the animals had come together.

The gathering brought together adults and younger eagle rays of different sizes

The gathering included both large and small individuals. Several eagle rays had an estimated disc width of more than 80 centimetres, while others measured about 20 centimetres, suggesting smaller animals were part of the population. The researchers estimated the rays’ size by comparing them with the food fish on the seabed, which were approximately 20 centimetres long. Among the individuals that could be examined closely enough to determine their sex, all appeared to be female because researchers did not observe male reproductive structures known as ‘claspers.’ However, the study did not rule out the presence of males elsewhere in the group. The sighting also occurred during a period that roughly overlaps with the species’ breeding season in the west and central Mediterranean. Yet the researchers could not determine whether reproduction played any role in the gathering and concluded that feeding appeared to be the primary explanation.

The tuna ranch may be changing the dietary habits of the eagle rays

Common eagle rays mainly feed on ‘molluscs,’ although fish can also form part of their diet. The abundance of food beneath the tuna cages may therefore provide the animals with an easy feeding opportunity. The study suggests that this could temporarily alter their normal feeding behaviour and encourage the rays to remain near the ranches while food is available. During fallow periods, when the farms are not feeding tuna, their diet and behaviour may return to usual patterns typical of the surrounding Maltese waters. The findings illustrate how aquaculture operations can influence nearby wildlife. Food that escapes or falls from fish farms can affect ‘where wild animals gather and obtain part of their diet.’

What does the record eagle ray gathering mean for conservation

The discovery has particular conservation significance because the common eagle ray is classified as vulnerable in the Mediterranean. The gathering of such large numbers in one location could create both opportunities and risks. The researchers noted that predictable concentrations could make the rays easier to target by fishers. Although there is no fishery specifically targeting eagle rays in Malta, the species is caught and traded in other parts of the Mediterranean.The study suggested that additional fishing restrictions around the tuna ranches could help protect these aggregations. At the same time, the researchers warned that aquaculture sites can alter the natural movement patterns and behaviour of wild marine animals. Continued monitoring could help determine whether the Malta gathering was an isolated event, a seasonal occurrence or part of a pattern linked to feeding activities at the tuna ranches. The extraordinary sighting has opened a new window into the behaviour of a species whose large gatherings have remained poorly understood.