Fatty acid composition and parasitism of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) populations in the northern Catalan Sea in the context of changing environmental conditions.

Sebastian Biton-Porsmoguer,Ricard Bou,Josep Lloret,Elsa Lloret,Manuel Alcaide,Steven Cooke

doi:10.1093/conphys/coaa121

Abstract

The status of sardine and anchovy populations in the northern Mediterranean Sea has been declining in recent decades. In this study, fatty acids and parasitism at different reproductive and feeding stages in these two species were assessed using specimens caught along the northern Catalan coast, in order to assess the links between lipid dynamics, reproduction and feeding in these two species and to contribute towards an explanation of the potential causes of the current poor situation of the stocks. The results support the use of fatty acid levels as indicators of the body condition of sardine and anchovy at different reproductive and feeding stages, as well as that of the pelagic environmental conditions. In particular, the relatively low n-3 polyunsaturated fatty acid levels found in spawning sardines compared to spawning anchovies indicate a poorer reproductive health status of sardine. By comparing the current total lipid content values with those recorded in other Mediterranean and North Atlantic areas, and others from more than 10years ago, in the adjacent area of the Gulf of Lion, our study reveals the persistent poor condition of sardine and anchovy in the northern Catalan Sea. Furthermore, the low levels of diatom fatty acid markers observed throughout the spawning and non-spawning seasons in both sardine and anchovy indicate a diet poor in diatoms. Moreover, the results indicate that it is very unlikely that parasitism is a significant factor in the decline in condition of sardine and anchovy in the northern Catalan Sea. In fact, the results, which we believe provide useful insights for the management of small pelagic fisheries in the Mediterranean, suggest that the current poor condition of sardine and anchovy in the northern Catalan Sea has probably been exacerbated by a decrease in plankton productivity and/or a shift in the taxonomic composition of phytoplankton communities, adding to the ongoing effects of overfishing.

Highlights

Fatty acids and parasitism at different reproductive and feeding stages in these two species were assessed using specimens caught along the northern Catalan coast, in order to assess the links between lipid dynamics, reproduction and feeding in these two species and to contribute towards an explanation of the potential causes of the current poor situation of the stocks
By comparing the current total lipid content values with those recorded in other Mediterranean and North Atlantic areas, and others from more than 10 years ago, in the adjacent area of the Gulf of Lion, our study reveals the persistent poor condition of sardine and anchovy in the northern Catalan Sea
The results from this study provide evidence that fatty acid levels are good indicators of the body condition at different reproductive and feeding stages of small pelagic fish and of pelagic environmental conditions in the context of global change

Summary

Introduction

Substantial declines in the stock size, mean body size and/or condition of European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) have been observed in the north-western Mediterranean Sea since 2009 (Van Beveren et al, 2014; Brosset et al, 2015, 2016a, 2017; Ferrer– Maza et al, 2016; Albo-Puigserver et al, 2017, 2019; Saraux et al, 2019), resulting in profound changes in the structure of the stocks and a major decline in the landings and fishing activity (Brosset et al, 2017; Coll and Bellido, 2019; Saraux et al, 2019). Overfishing, climate change, diseases, predation by large fish such as tuna and competition between pelagic organisms for the zooplankton they feed on have all been suggested as factors to explain the decline in abundance and mean weight of sardine and anchovy populations in the Gulf of Lion It seems, that the combined effects of poor condition, slower growth and the disappearance of older and larger individuals mediated by potential changes in food availability have been the major causes (Saraux et al, 2014; Van Beveren et al, 2014; Saraux et al, 2019). In the Bay of Biscay, the decline in body condition in sardine since the late 2000s had no apparent link with fishing pressure but instead was linked to trophic responses involving a potential shift in the timing of the secondary production and/or the quality of the food (Veron et al, 2020)

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Conclusion