Larval trophic ecology of small pelagic fishes: a review of recent advances and pathways to fill remaining knowledge gaps

ABSTRACT: Early life stages constitute a bottleneck for most fish populations, particularly for small pelagic fish (SPF), for which the interannual variability in recruitment strength is very high, and recruits frequently constitute the bulk of the population biomass. Finding the right prey (in terms of size and quality) during these early stages is critical for recruitment success. In this work, we synthesize the available literature on the trophic ecology of the early life stages of SPF, particularly clupeiforms. Works published during the last decade (2013-2022, 37 papers) were compared to those published previously (1920-2012, 107 papers). Gut content analysis of field-caught larvae is still the most commonly used technique (44%), while the use of biomarkers (e.g. stable isotopes and fatty acid composition), molecular tools (e.g. metabarcoding) and multitrophic approaches has increased in the last decade. Significant new knowledge was gained recently, such as that on larval feeding rates and behavior through laboratory experiments for species kept in culture (e.g. Atlantic herring, Pacific and Atlantic sardines), but some old challenges remain, such as the high vacuity rates of field-caught larvae. Lastly, we provide recommendations for future studies, such as the use of complementary techniques, the importance of studying ontogenetic shifts, the use of metabarcoding for analyzing the diet of early larvae that depend on microplankton, and the identification of prey with high taxonomic resolution. Such studies are essential to better understand larval growth and survival at sea, and thus to better understand and predict SPF population dynamics.