The availability of suitable prey during the early life of fish may determine recruitment to the adult population. Since larval and juvenile feeding can be highly selective, their preferences for certain prey species and sizes should be considered when estimating the availability of prey. In this study, diet composition (and prey preferences) of 4984 (1366) Faroe Plateau cod (Gadus morhua) larvae and juveniles between 3 and 63 mm sampled on the central Faroe shelf (62°N, 6.8°W) over an 8-year period was investigated. Cod preyed on successively larger food items as they grew. Yolk-sac larvae consumed phytoplankton, copepod eggs and nauplii before the yolk sac was exhausted. Copepod eggs followed by calanoid nauplii were the predominant and preferred food items in the early larval stage. In the late larval stage these were replaced by small to medium sized (0.6-1.2 mm) copepod species mainly Pseudocalanus sp., Acartia sp. and early stage Calanus finmarchicus, of which the two former species appeared most preferred. Temora longicornis was highly abundant in juvenile cod, but the preference for this species was neutral. Positive selection and high abundance of late stage (≥ 1.5 mm) C. finmarchicus was observed in early juveniles, but C. finmarchicus was replaced by decapod larvae in late juveniles. Other abundant prey species such as Oithona sp. and barnacle larvae occurred in varying numbers in the guts, but were generally not positively selected at any stage. Late larval and early juvenile cod appeared to suffer from unfavourable feeding conditions as they fed on smaller prey than what they prefer potentially indicating bottle necks in the feeding at these development stages.

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Recruitment to the Faroe Plateau cod (Gadus morhua) stock (62°N, 6.8°W) is highly variable between years, and availability of suitable prey during the early life stages may determine the year class strength. Here we first investigate interannual variability in recruitment (1983–2017) of cod based on survey data and data from stock assessments. Positive relationships between the spawning stock biomass and larval abundance and between juvenile abundance and recruitment at year 1 were detected. However, the relationship between larval abundance and juvenile abundance was not statistically significant, indicating variable survival during the larval/early juvenile stages. We then investigated if food availability at the larval and early juvenile stages could explain the variability in recruitment using an 8-year long time series of larval and juvenile gut content. Feeding at the early larval stage, present during the pre-bloom, was relatively stable between years. However, large interannual variability in feeding at the early juvenile stage was detected. When juvenile survival and mean length were high, juveniles clearly had less food in their guts. This contradiction is suggested to be due to intense grazing pressure on the zooplankton at high juvenile abundances. However, years with high larval survival coincided with years when the phytoplankton spring bloom was early and intense, suggesting that production of suitable prey during the larval stages determines larval growth and survival and that this production is dependent on the phytoplankton spring bloom characteristics.