Plattform Platform	Reise-Nr. Cruise-No.	Zeitraum Period	Projekt Project	Arbeitsgebiet Working area
Tridens II	HERAS 2014	23.06.2014 - 18.07.2014	HAS	North Sea

Fahrtleiter Chief Scientist	Institut Institute	Auslaufhafen Port of departure	Einlaufhafen Port of return	Stationskarte Station map	Schiffsroute Trackchart
Fassler Sascha	IMARES, Wageningen UR, Institute for Marine Resources and Ecosystem Studies, Texel	Scheveningen	Scheveningen

Ziel der Reise / Objectives of Cruise:

The objective was to carry out an hydro acoustic survey defining the abundance of herring and sprat in the North Sea, in co-operation with the institutes of Norway, Scotland, Denmark, and Germany. Calibration of the echosounder in a sheltered area, preferably at Scapa Flow, Orkneys 58?56'71N - 003?00'57W. The first week of the whole 4 week survey period was used for calibration of the acoustic equipment in a sheltered location on the Orkney Islands. Departure from Scheveningen was on Monday 23 June and Tridens steamed up north-west towards the proposed calibration location in Scapa Flow, UK. Arrival in Scapa Flow was in the morning of Wednesday 25th June. Calibration of the acoustic equipment took place during the following 2 days on 25th/26th June and was completed before the vessel departed again. Conditions at the calibration site were very favourable and good calibration results could be achieved. Tridens then steamed to Aberdeen for an extended weekend break before it left again the following Monday to start conducting the survey. The survey continued according the planned transects until Thursday 10th July. Due to bad weather between Wednesday 9th and Thursday 10th July, the towed body housing the echosounder transducers got damaged. In the morning, it was evident that the steal towing cable was torn. The towed body was then only attached at the transducer data cables and a Dyneema rope which was wound up tight around a winch on the back deck. The result was that the towed body got closer to the ship than usual and was tight against its starboard side. Waves and swell were smashing it against the boat causing bent metal and fractures in the frame. In the morning of Thursday 10th July, about 6 hours were lost for repairs (exchanging metal pieces of the towed body, welding on new stabilising weights, and repairing damages to the transducer cable). Therefore, the planned transect coverage had to be compromised (see "Deviations from the proposed station grid") in order to reach the end of the transect in time before the agreed weekend stop in Newcastle. After that incident, the survey could be conducted as planned. During the standard survey protocol, 3 pilot trawls just below the surface aimed at mackerel were conducted successfully. The chosen survey setup (1 week calibration/gear trials, followed by 3 weeks of survey transect coverage) proved again to be an optimal solution to complete the transects in good time with adequate possibilities for trawl samples (to guarantee a good survey precision), before the scheduled weekend breaks. Arrival in Scheveningen after the survey was on Thursday 17 July with an ETA of 19:00 UTC. Since 2010, cruise leaders keep a weblog during the survey, which can be found at: http://herringsurvey.blogspot.nl

Messungen / Measurements