COMPARISON OF CATCH RATES AMONG SMALL AND LARGE BONGO SAMPLERS FOR CALANUS-FINMARCHICUS COPEPODITE STAGES

Comparison of catch rates between small (20-cm, 0.165-mm-mesh nets) and large (61-cm, 0.333- and 0.505-mm-mesh nets) plankton samplers was carried out for Calanus finmarchicus copepodite stages sampled simultaneously during six different times. It is concluded that C. finmarchicus stages CI and CII were undersampled in 0.333-mm-mesh samples, while stages CIV-CVI were undersampled in 0.165-mm-mesh samples. Stage CIII catch rates were not different for these two samplers. Comparison of catch rates between 0.165- and 0.505-mm-mesh samples demonstrated that stages CI-CIII were undersampled in the 0.505-mm-mesh samples, stages CV and CVI were undersampled in the 0.165-mm-mesh samples, and there was no difference in catch rates for stage CIV. There was evidence of substantial variability in results among cruises for most stages. This is attributed to inherent variability associated with plankton sampling due to their patch distribution. Due to the large variation in catch rates between these different samplers, it is recommended that the appropriate sized sampler be used to collect different stages of C. finmarchicus copepodites rather than attempting to correct for catch rate differences among different sized samplers.