Prey or predator—expanding the food web role of sandeel Ammodytes marinus

Abstract

We report an unexpected observation of lesser sandeel Ammodytes marinus foraging on juveniles and late larval stages of the same species. This recording sheds new light on the can- nibalistic and piscivorous capacity of forage fish and raises a number of questions about the role of forage fish in marine food webs. In 2012 and 2013, the stomachs of 748 sandeels from 36 differ- ent commercial sandeel hauls in the central North Sea were opened, and 9% of these contained late-stage sandeel larvae. In order to better understand the cannibalistic nature of sandeels, we made a detailed analysis of another 450 sandeels from a single haul with a high frequency of apparent cannibals. One-third of the stomachs contained a minimum of 1 young sandeel (mean length 2.7 cm; max. length 4.9 cm), 10% contained 5 or more, and 1 stomach contained 18. Analy- ses of sample DNA confirmed that predator and prey were conspecifics. Larger specimens were more likely to be cannibals. Among cannibals, however, the specific sandeel larvae consumption was independent of cannibal size. We argue that this piscivorous cannibalistic behaviour may not only be a key factor in explaining recruitment fluctuations in North Sea sandeel stocks, but it may also add a new element to the complexity of energy flow in marine food chains.