International North East Atlantic hydro acoustic survey for blue whiting. The survey is coordinated by ICES and has been executed annually. Ireland, Russia, Iceland, Denmark, Faroes and Norway also participate in the survey.
The purpose of the survey is to estimate the blue whiting stock of the North East Atlantic. The ICES uses this estimation is as a "tuning index" to assess the North East Atlantic blue whiting stock. For this survey a Simrad 38kHz splitbeam transducer was used together with a Simrad EK60 echo sounder. The applied method was echo integration. By sailing transects over the survey area, the total acoustic cross-section can be calculated by surface area sampled. Trawling identified species composition of localized schools. The length composition of each species was determined. Blue whiting was examined on age and fecundity from which a split up stock structure was made. Blue whiting where found throughout the survey area associated with the continental shelf edge but showed a clear increase reaching the northern part of the Tridens survey area.
Although a considerable loss of transects due to bad weather conditions, the survey has been successful in terms of acoustic data quality and inter vessel communication. Due to bad equipment Tridens was not able to meet international agreements (PGNAPES) on CTD downcasts.
Sytse Ybema (Institute for Marine Resources and Ecosystem Studies, IJmuiden)