Article: When sharing isn't caring: sociality of marine mammals vulnerability to the spread of infectious diseases
When sharing isn't caring: sociality of marine mammals vulnerability to the spread of infectious diseases
As part of the Research Team at ORRCA, we’re committed to sharing the newest insights and discoveries shaping the marine mammal world. Our goal is to break down fresh research into accessible, meaningful stories that highlight why this science matters - for our marine mammal species, for the ocean, and for the communities who care about them.
There is no shortage of pressures facing marine mammals today. Climate change, pollution, and human disturbance are reshaping the oceans at a pace these animals have never experienced, and our marine mammals are living in trying times. Infectious diseases pose a serious threat to marine mammal populations that are already under stress.
The recent COVID-19 pandemic reminded us how profoundly social behaviour can shape how diseases spread through populations. For marine mammals, understanding how their social interactions may spread pathogens, as well as understanding the patterns of social interactions themselves, is essential for conservation, outbreak response, and designing targeted interventions (such as vaccinating key individuals or populations).
Researchers at the Cetacean Ecology, Behaviour, and Evolution Lab at Flinders University in South Australia set out to what science currently knows about marine mammal sociality and disease. They conducted a systematic review of the global literature on marine mammal social structures and their influence on infectious disease transmission.
After scanning 1,920 papers, the researchers found only 14 studies that directly examined marine mammal social structures and infectious disease transmission, and that used social network analyses (or epidemiological modelling).
Across the papers, they found the following key findings:
- Social connectivity increases disease risk – across several species, individuals with stronger or more frequent associations with other individuals were more likely to transmit and acquire diseases.
- There can be “super-spreaders” within marine mammal communities – there are individuals that are highly central within populations and have many social connections, often acting as bridges for pathogens to move across sub-groups within a population. Identifying these key “super-spreader” individuals in the event of an outbreak would be vital in order to direct vaccination efforts and is often suggested throughout the literature as an effective response strategy.
- Group structure will shape the outbreak size – fragmented networks (which are loose or have modular social structures) tend to limit the spread of disease throughout a population. In contrast, populations with highly connected subgroups can amplify and accelerate transmission. This means that not all social species are equally as vulnerable to disease transmission and that the pattern of connection within a species population matters more than the group size alone.
The review also highlighted that research in this space is extremely limited and there are several gaps in our collective knowledge. Most studies focus on bottlenose dolphins (who have what is known as a fission-fusion social structure where alliances change over time) and killer whales (which live in tightly woven matriarchal family groups). There are very few studies that examine pinnipeds or baleen whales. Most of the studies also focus on North America and Australia, meaning that there are large areas across the world that are data deficient in this space.
Given the increasing risk of disease transmission for marine mammals globally, there is a need for broader species analysis and greater geographic coverage, as well as an integration of environmental and ecological variables that may determine how vulnerable a population currently is to additional stressors such as diseases.
With this field of study still in its infancy and with diseases such as rabies and avian influenza entering marine mammal populations, the message is clear: protecting marine mammals in a rapidly changing ocean will require research that combines epidemiology, behavioural science, and conservation. Marine mammal social lives aren’t just fascinating, but are also key to understanding and managing disease risk.
