SMRU > Research > Disease
Diseases (both infectious and non-infectious) are being increasingly reported in a very wide variety of marine mammal species worldwide. Whether this is a true increase or a function of increased interest and effort is a matter of debate. Nevertheless, there has also been an increase in the global reporting of mass mortality events among marine mammals, involving both seals and cetaceans, and outbreaks of infectious disease or unusual mortality events due to biotoxins from harmful algal blooms.
The occurrence and epidemiology of marine mammal disease is very difficult to study in free-living animals. Often our knowledge of disease events in individuals comes from live stranded animals that are taken into rescue centres for rehabilitation or from those stranded dead that are then subject to comprehensive post mortem examination. Some studies can be carried out on free-living animals (e.g. the exposure to infection through serological testing, the occurrence of ectoparasites or skin disease or investigating the causes of mortality among neonatal pups) but as the majority of adult animals captured are healthy and disease-free this approach has obvious limitations. Retrospective analyses of samples collected from long-term studies of grey and harbour seals have provided useful information on exposure to infection, such as PDV.
Studies on the occurrence of disease in marine mammals have generally been collaborative projects with the UK Cetacean Stranding Investigation Programme and the Scottish Marine Animal Stranding Scheme which collects temporal and spatial disease data from animals that wash ashore or are bycaught in fishing nets. In addition organisations involved in the rescue and rehabilitation of seals, such as the RSPCA and SSPCA, assist in the study of disease, particularly among seal pups and juveniles that are the most common age group stranded alive and taken in for rehabilitation. The recent decline in the abundance of harbour seals, particularly in Scottish waters, prompted a study into the health of these animals and although no signs of infection or systemic disease were seen, animals had been exposed to toxins from harmful algae, particularly domoic acid and saxitoxin. These toxins cause Amnesic and Paralytic Shellfish Poisoning when ingested by humans so further research into whether they may be causing similar disease in harbour seals is currently underway.
Ailsa Hall, Mike Lonergan, and Paddy Pomeroy studied the impact of disease events and mass mortalities on populations and as such have been central to the UK response and follow up during the two outbreaks of phocine distemper virus (PDV), largely among harbour seals that occurred in 1988 and 2002. Ailsa Hall currently has students studying the risk of biotoxin exposure on harbour seals and pathogen exposure in grey seals.