Possible vessel avoidance behaviour of capelin in a feeding area and on a spawning ground

The avoidance reactions of Barents Sea capelin (Mallotus villosus) to Norwegian research vessels were studied by means of the Bergen Acoustic Buoy (BAB), which was equipped with a Simrad EK60 echo-sounder operating at a frequency of 38 kHz. BAB experiments were carried out in the capelin's feeding area in the Barents Sea in the autumn and on its spawning grounds in Varangerfjord in Northern Norway in early spring. The vessel approached the BAB at normal survey speed (approximately 11 knots), eventually passing it at a short distance (5-25 m). Changes in the volume scattering coefficient and in the centre of the depth distribution under the BAB were analysed. There was no significant influence of the avoidance reactions of capelin to survey vessels on the volume scattering coefficient, either in the feeding area or on the spawning ground. However, there were indications of changes in the centre of depth distribution (diving) before the pass, especially in dense concentrations on the spawning grounds. An analysis of the time of start, maximum and end of a possible avoidance reaction using a fitted polynomial, indicated that there might be an avoidance reaction with a defined start, but not a defined end within a +/-5 min range. The authors propose that the selective process relating to capelin might favour maximising its ability to flourish by concentrating on feeding and reproduction. (C) 2004 Elsevier B.V All rights reserved.