The response of herring to high crowding densities in purse-seines: Survival and stress reaction

Abstract

To study the effects of crowding in purse-seines on the survival and stress response of herring (Clupea harengus), large-scale field experiments were conducted in the North Sea during 2008 and 2009. The mortality was 28 at a crowding density of 221 kg m-3 and increased further with increasing density. Crowding densities <150 kg m-3 did not result in any additional mortality compared with the control group (0.92.0). Smaller herring and herring with a lower condition factor were more vulnerable to the effects of crowding. Blood analyses showed a significant increase in cortisol, lactate, and blood ions in the crowded fish. Lactate returned to control levels 2 d post-stress, whereas cortisol and blood ion levels continued to increase during the 4-to 5-d monitoring period. Furthermore, plasma glucose appeared to be substantially reduced at the end of the trial, indicating that the herring were incapable of restoring homeostasis and were approaching energy exhaustion. These results provide important information about the crowding densities that can be tolerated in the purse-seine fisheries for herring and will benefit future development of guidelines for purse-seine slipping operations. © 2012 International Council for the Exploration of the Sea. Published by Oxford University Press. All rights reserved.