Turbulence enhances feeding of larval cod at low prey densities

Abstract

The ability of larval fish to find food successfully after hatching is critical for their growth and survival during the early life stages. However, the feeding ecology of larval fish is strongly dependent on prevailing physical and biological conditions. Small changes in the prey distribution, turbulence, light, and ocean temperature can affect larval survival probabilities. This study combined physical and biological observations collected from Atlantic cod (Gadus morhua) spawning grounds from Lofoten, Norway, during the years 1991-1992 with an individual-based model (IBM) that is able to simulate behaviour, feeding, and growth. Observational data on the vertical distribution of larval cod revealed that they congregated at 10-25mduring the day, although the highest abundance of preywas generally in the upper 10 m. Using the behavioural component of the IBM, we analysed the mechanistic interactions between larval bioenergetics and the physical-biological environment and compared modelled with observed vertical larval cod distribution. During periods of both low and high prey densities, turbulence had a significant impact on larval cod feeding and growth rates as well as on larval vertical distribution. At low prey abundance (<5 nauplii l-1), turbulence enhanced encounter rates were very important for sustaining ingestion and growth rates for first-feeding larval cod. Our results suggest that turbulence allowed larval cod to sustain high ingestion rates even deeper in the water column, where prey densities are usually lower.