Vertical migration of Norwegian spring-spawning herring larvae in relation to predator and prey distribution

Abstract

A diel vertical migration (DVM) pattern of Norwegian spring spawning herring (Clupea harengus) larvae was investigated during 19 and 20 April 2009. Factors influencing DVM included physical and biological properties of the water column. Data on larvae, prey and predators were collected with a depth-stratified multisampling device, inshore of Sklinna bank, close to the Norwegian coast, while light conditions were calculated using a Matlab® algorithm. A type I DVM pattern (i.e. deep during daytime, shallow at night) was observed for herring larvae, mainly occurring above the thermocline. No size-dependent differences were observed for larval vertical positioning. The highest overlap in depth distribution with their main prey was observed during daytime, when larvae were distributed deeper in the water column. From acoustics and macroplankton trawl data, a type I DVM was also observed for krill, although their concentrations were relatively low in the area. Cumulative predator–prey overlap plots suggest that krill most likely forage on copepods and smaller organisms. During the day, larvae concentrate near the thermocline to feed, while they move towards the surface at dusk, possibly to use the remaining light to continuing feeding. During the night, when light levels were too low to feed, larvae spread out in the water column above the thermocline. This migration pattern reduces the overlap between larvae and potential predators such as krill, which also move higher up during nighttime. It is suggested that the pattern of herring larvae DVM is a behavioural response to active pursuit of prey.

Keywords:

• Vertical migrations
• Clupea harengus
• predator–prey interactions
• fish larvae

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CORRIGENDUM

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

Special thanks go to everyone on board of RV ‘Johan Hjort’, April 2009, for helping with the sampling procedure. Furthermore, thanks to Laura Rey and Padmini Dalpadado for the help at the zooplankton laboratory; Ruben Patel and Tor Knutsen with acoustics scrutinizing; and Melle Webjørn with macroplankton trawl information. This work was funded by the Institute of Marine Research.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark