Opportunities and challenges for managing European smelt (Osmerus eperlanus); a threatened UK species

Ecological data on Osmerus eperlanus, also known as the European smelt, is extremely limited in the United Kingdom. The small diadromous species which belongs to the Osmeridae family is found in the Northeastern Atlantic from the White Sea to the western coasts of France including the Baltic Sea, Southern North Sea and British Isles (McAllister 1984). A report on the status of Smelt in the UK, published in 2003 suggested that there are approximately 21 populations around the coasts of England (19) and Wales (2) (Maitland 2003). Smelt populations have declined across Europe, with the fish now considered a rarity within the Thames.

Little is known about the parasite fauna of smelt in general, with even less known about the populations living in the UK. A recent survey by Pilecka-Rapacz et al. in 2017 suggested that only one historical publication was available on the parasitic fauna of smelt in the UK. Studies from the Gulf of Bothnia and Finland account for approximately 70% of the historical literature (Pilecka-Rapacz et al. 2017). Russia has also produced a number of publications however these papers are very hard to access and most are not written in English.

Annual surveys by the Environment Agency together with the Smelt Project survey run by the Zoological Society of London (ZSL) have been monitoring the smelt populations within in the tidal Thames and greater UK. Their samples have revealed an increasing prevalence of xenomas (cysts) within the gut of young-of-the-year smelt. The smelt have been identified to be infected with a microsporidian parasite, tentatively identified as Glugea hertwigi. This parasite has been identified in European smelt in the Baltic Sea and in Omerus mordax (Rainbow smelt) in Canada and the USA (Pekcan-Hekim, Rahkonen and Horppila 2005). Most publications on G. hertwigi were published in the 1970s and 80s, with few modern publications. The parasite has been shown to cause mortality through starvation and intestinal poisoning as a result of large xenoma masses in the stomach and intestine (Nepszy and Dechtiar 1972; Pekcan-Hekim, Rahkonen and Horppila 2005; Costa, Melo-Moreira and De Carvalho 2016). The increasing presence of this parasite in compromised populations in the Thames is of concern.

This project will be supported by the Environment Agency. The first aim is to validate the species of Glugea using molecular techniques and provide histopathological observations, which will then be published. This project aims to further the knowledge about the life history of the European smelt in the UK, identify potential threats to the species and access ways to conserve and restore declining populations