Feeding of European pilchard (&lt;em&gt;Sardina pilchardus&lt;/em&gt;) in the northwestern Mediterranean: from late larvae to adults

David Costalago,Isabel Palomera

doi:10.3989/scimar.03898.06d

Abstract

Summary: We assessed the relative importance of different prey types of the European pilchard (European sardine) from the late larval to the adult stage. Two different methodologies for analysing stomach contents were used to describe the trophic dynamics of sardine and the relationship of sardine feeding behaviour with the ontogenetic development of body structures used for feeding, such as gill rakers and pyloric caeca. This information is essential to accurately depict the use of the planktonic resources in the area by sardine and to discuss the extent to which the sardine population could be affected by environmental changes in the Mediterranean Sea. We showed that cladocerans in summer and diatoms in winter were numerically the most important prey types for both juveniles and adults. However, decapod larvae were the most important prey during all seasons in terms of carbon content. Accordingly, differences in methodology should be considered in the analysis of sardine diets. An analysis of the composition of the plankton showed that small copepods were strongly selected by sardines at all ages and in both seasons. We also observed that the pyloric caeca began to grow when the sardines were approximately 4-5 cm standard length (SL) and ended their development when the sardines reached approximately 8 cm SL, whereas the gill rakers appeared to be completely functional when the sardines reached 7 cm SL. Therefore, filter feeding of small particles could be performed with total efficacy beginning at 7-8 cm SL. In view of the energetic advantage of filter feeding in a well-adapted filter-feeding species such as sardine, the prospective limited availability of small particles hypothesized by certain authors for the Mediterranean could have negative consequences for sardine. This study demonstrates that sardine populations, given their extremely high dependence on the lower marine trophic levels, could be strongly affected by alterations in the environment and in the planktonic community.

Highlights

Most marine fish ecologists consider that the dietary habits of a fish species may depend upon both the availability of prey (Frederiksen et al 2006) and the anatomy of the fish (Gerking 1994, Wainwright et al 1995)
The number of gill rakers (GR) maintained a significantly positive trend (p
Pyloric caeca in sardines were first observed in specimens of 4 cm SL

Summary

Introduction

Most marine fish ecologists consider that the dietary habits of a fish species may depend upon both the availability of prey (Frederiksen et al 2006) and the anatomy of the fish (Gerking 1994, Wainwright et al 1995). The European sardine or pilchard, Sardina pilchardus, is a rapidly growing and short-lived small pelagic fish species It is one of the most important fish resources throughout its range in the northeastern Atlantic, from the North Sea to the Senegalese coast, including the Mediterranean and the Black Seas. Studies of its feeding dynamics have been conducted on the Atlantic coast of Spain, where the diets of juvenile and adult sardine have been found to consist entirely of plankton (Bode et al 2004, Garrido et al 2007, 2008) and where adults are able to perform both filter and particulate feeding Due to this difference between stages, the adults show a greater fraction of phytoplankton in their stomachs than the juveniles do. It has been shown that sardine larvae in the same region generally feed on copepods (Conway et al 1994, Munuera and González-Quirós 2006)

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