Molecular barcoding reveals patterns of egg predation in small pelagic fish

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Cannibalism and intraguild predation occur in a vast number of small pelagic fish (SPF) species. Egg and larval predation can have important consequences on mortality, and its accurate assessment is important to estimate the impact on recruitment strength and population dynamics of predators and prey. Such assessments are hampered by limitations in visual species identification of many fish eggs and larvae in the predators’ stomachs. European sardine Sardina pilchardus and Atlantic chub mackerel Scomber colias, the dominant species of the pelagic food web off the Canary Current Upwelling ecosystem, are major predators of fish eggs. Egg predation by these SPF species is particularly high on sardine and anchovy eggs, but many preyed fish eggs are not amenable to visual identification. This study provides a proof-of-concept application of molecular identification of diverse fish eggs from SPF stomach contents not suitable for visual identification, as a way to improve our understanding of the impact of intraguild predation on fish population dynamics. Results show a high diversity of fish species in the eggs ingested by sardines and chub mackerel (18 and 15 families, respectively), mostly comprising locally abundant coastal taxa. Sardine ingested predominantly anchovy, sardine and sparid eggs, while chub mackerel ingested predominantly sparid eggs, followed by serranid (Serranus spp.) and sardine eggs. Sardines also showed higher variability in prey composition compared to chub mackerel. Exploratory analyses also suggested variability in prey composition with sampling area, season and maturity stage for sardine and chub mackerel, highlighting the need for dedicated follow-up studies.