An analysis of 0+barbel (Barbus barbus) response to discharge fluctuations in a flume

We studied the response in velocity use and time in refuge of 0+ juvenile barbel (Barbus barbus) to an increase in discharge in a flume. Each of five treated and five control fish were observed individually in separate eight-hour experiments. Observations (trials) were arranged into a hierarchically structured, semi-randomized sampling schedule consisting of four time levels: phase (4 h) D period (2 h) D sub-period (30 min) D trial (120 s). Increased discharge caused treated barbel to use higher velocities than control individuals, with individual differences in behaviour present at the various temporal tiers. Individual responses were modelled as either random-walk or short-memory processes, and those by treated fish were generally abrupt and permanent, with only one individual showing a gradual and permanent use of the higher velocities. Time in refuge was not affected by increased discharge, except for one fish that sought shelter after intervention. There was a significant relationship for most treated individuals between selection of lower velocities and time in refuge, and most barbel (both treated and control) showed significant deviations of used from mean flume velocities. The potential of the proposed approach to assess memory-based individual fish responses to discharge and its consequences for (PHABSIM-oriented) behavioural studies is discussed, and the mosaic of barbel behaviours observed is compared with available laboratory and field studies. Copyright (c) 2005 John Wiley & Sons, Ltd.