Abstract
Simple SummaryDisease factors and mortality etiologies of free ranging wild cetaceans such as the harbour porpoise (Phoceona phocoena) are difficult to study. However, stranded animals and carcasses can provide invaluable information on the health and biology of this species. Post-mortem examinations performed on 128 stranded harbour porpoises collected over 15 years from Swedish waters examined general health, disease findings and cause of death. The main cause of death was bycatch in fishing gear (31%, confirmed or suspected). Disease, most often pneumonia, was also a frequent cause of death (21%). Porpoise population health may mirror the overall health and stability of marine ecosystems and the effects of human activities on coastal environments. Monitoring health, diseases and causes of death of porpoises allows for identification of threats to these animals, to other animals, to humans and to the environment.Harbour porpoises (Phocoena phocoena) are useful indicators of the health of their wild populations and marine ecosystems, yet their elusive nature makes studying them in their natural environment challenging. Stranded porpoises provide an excellent source of data to study the health and biology of these animals and identify causes of death, diseases and other threats. The aim of this study was to document pathology, and where possible, cause of death in porpoises from Swedish waters. Post-mortem examinations were performed on 128 stranded porpoises collected from 2006 to 2020. Overall, bycatch including definitive and probable cases was the most common cause of death (31.4%), followed by disease (21.3%), predominantly pneumonia. In adults, infectious disease was the most common cause of death. Bacteria with zoonotic potential such as Erysipelothrix rhusiopathiae and Brucella sp. were documented for the first time in porpoises from Swedish waters, as was the porpoise-adapted group B Salmonella enterica ST416/ST417. Three of four deaths from non-infectious diseases involved parturition complications. Four cases of suspected predation were documented, but further analyses are required to confirm these findings. Our results are consistent with those from other regions in Europe and serve as a reference for future monitoring for changing patterns of health and disease of porpoises and their environments.
Highlights
Harbour porpoises (Phocoena phocoena) are small, coastal cetaceans that inhabit subarctic and temperate waters of the Northern hemisphere
Six porpoises in this study were collected from the overlapping area of suggested population management borders for the Belt Sea and Baltic Sea porpoise populations (Figure 1) and genetic analyses are ongoing to determine the origin of these animals
This study provides an important first description of causes of death, diseases, pathology and potential population threats in porpoises inhabiting Swedish waters and serves as a reference for future monitoring of trends
Summary
Harbour porpoises (Phocoena phocoena) are small, coastal cetaceans that inhabit subarctic and temperate waters of the Northern hemisphere They are the only cetacean species that resides in Swedish waters year-round. Porpoises are top predators in marine ecosystems They have a relatively short life span compared to other top predators such as seals, dolphins and whales [3] and a comparatively more intensive reproductive cycle including earlier maturation and more frequent reproduction when compared with other odontocetes [4]. Their nearshore habitat makes them vulnerable to anthropogenic activities, which include incidental bycatch in fisheries, pollution, noise and marine traffic [5,6]. Data from stranded porpoises in other parts of northern Europe and
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