Avoidance of a midwater frame trawl by herring larvae

Abstract

Analysis of a time series of samples, taken with a large opening and closing frame trawl at a fixed position in the North Sea in January 1988. identified two sources of variability in the depth-integrated catch rates of herring larvae. For larvae smaller than 25 mm, variability over the 45-h sampling period was mainly accounted for by lateral advection of a horizontally patchy distribution past the sampling position. However, visually cued diurnal changes in avoidance of the gear accounted for most of the variability in catches of larvae between 25 and 40 mm long. The results were consistent with the development of sensory abilities with increasing length of the larvae and consequent decrease in the probability of capture by foraging predators. © 1990 Oxford University Press.