The curious incident of porpoises killed by ‘dog-bite’ bacteria
Scientists from a wide range of backgrounds have pooled their resources to solve the mystery of a ‘dog-bite’ bacteria attributed to the death of harbour porpoises.
In a study led by researchers at Scotland’s Rural College (SRUC), microbiologists, pathologists and ecologists took a forensic approach to identify the bacteria in wounds found on harbour porpoises stranded in Scotland, England, the Netherlands and Belgium. However, the mystery deepened when they identified it as Neisseria animaloris –previously linked to human infections following dog bites.
Lead researcher Geoff Foster, a microbiologist with the Scottish Marine Animal Stranding Scheme – part of SRUC, said: “We realised it was unlikely that porpoises would be bitten by a dog. “Subsequent investigations indicated that the porpoises had been attacked by grey seals. Such attacks can be fatal, but in the cases of the animals involved in this investigation, the porpoises appear to have survived the initial assaults, only to die later of infections introduced from the mouths of seals during the attacks.”
Previous research found that grey seals are an important predator of porpoises, with seal attacks among the most common causes of death in this small whale species. This new study, published by Nature’s Scientific Reports, has now shown that porpoises that survive the initial attack may still die as a result of the bite injuries.
Co-author and lead researcher in the Netherlands, Lonneke IJsseldijk, said: “A predator never has a 100% kill. There are always animals that escape. But for these porpoises this did not end well: after a long agony, these bitten porpoises still died.”
The research highlights a potential risk to humans, with Neisseria animaloris having a so-called zoonotic potential, which means that people can become infected with it.
Lonneke, who works in the Faculty of Veterinary Medicine at Utrecht University, said: “People should be careful if they come into contact with curious seals on the beach or while swimming.” She added, “Grey seals have only been found in the southern North Sea since the 1980s, with their numbers rising to several thousand nowadays. Porpoise numbers in the southern North Sea have also risen in the last few decades, leading to increased encounters between the species – and a possible explanation for the rise in seal-related porpoise mortality recorded in this particular area.”
Geoff said: “The number of porpoises killed directly or indirectly from these attacks will be higher than initially anticipated. “This work highlights a previously unknown consequence of grey seal attacks on porpoises that is of relevance to scientists studying the threats to other wild populations, as grey seals also attack other marine mammals.”
The research was carried out by SRUC and Utrecht University in partnership with the Animal and Plant Health Agency (APHA), Moredun Research Institute, Public Health England, Cetacean Strandings Investigation Programme, Agri-Food and Biosciences Research Institute, Erasmus University and Wageningen Bioveterinary Research.
The research was funded by the Scottish Government, UK Department of Environment, Farming and Rural Affairs (Defra) and the Dutch Ministry of Agriculture, Nature and Food Quality.