Can pathogens alter the population dynamics of sardine in the NW Mediterranean?
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Sardine populations worldwide can fluctuate drastically over short time periods, in terms of both biomass and biological characteristics. Fluctuations might be amplified by pathogens, but such hypotheses have never been considered in the absence of clear macroscopic symptoms. In the Gulf of Lions (NW Mediterranean), an enduring severe decrease in sardine (Sardina pilchardus) size, condition and age has been observed since 2008, resulting in a strong decline in landings. This situation might have been caused or aggravated by diseases, especially as other drivers such as fisheries are not expected to be important. Therefore, we developed and performed a general veterinary study, aimed at detecting a wide range of potential pathogens, including parasites, viruses and bacteria. We explored which infectious agents are most likely to produce a causal relationship with sardine health, important information for future infection experiments. Among about 1300 sardines sampled during June 2014–July 2015, microscopic parasites (often trematodes and coccidians) and bacteria Tenacibaculum and Vibrio spp. were found. However, no clear damage to tissue was observed and there was generally no link between the agents’ presence and host size or condition, so that no strong indications of pathogenicity were present. Nonetheless, 54 % of the sardines analysed in 2015 had elevated quantities of melano-macrophage centres (macrophage aggregates), indicating stress on the fish that might potentially be related to starvation and/or pollution.
KeywordsVibrio Fish Condition Sardina Pilchardus Sardine Population Lean Fish
We would like to acknowledge J.-F. Bernardet (Institut National de la Recherche Agronomique) for the characterisation of Tenacibaculum, J.-C. Raymond (Comité National des Pêches Maritimes et des Elevages Marins) for his useful comments on the results and the manuscript and D. Duplisea (Fisheries and Oceans Canada) for the thorough language editing. We also thank the captain and the crew of the RV “L’Europe” as well as all the scientists on board for their assistance during the PELMED surveys. PELMED surveys are cofinanced by Europe through the Data Collection Framework. Our gratitude is extended as well to the MEDITS team and the fishermen who provided us with sardine samples. We would also like to thank the two anonymous reviewers, whose suggestions greatly improved the manuscript. This work is a part of the programme EcoPelGol (Study of the Pelagic ecosystem in the Gulf of Lions), financed by France Filière Pêche (FFP).
Compliance with ethical standards
Conflict of interest
The authors declare no competing financial interests or conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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