WOBEC SOP RMT

Weddell Sea Observatory of Biodiversity and Ecosystem Change – WOBEC Standard Operating Procedures Technical Documentation December 2025 To be cited as Schaafsma, Fokje, Nils Van den Steen, Anton Van de Putte, and Hauke Flores. ‘WOBEC SOP RMT’. Zenodo, 15 December 2025. https://doi.org/10.5281/zenodo.17935936. Co-funded by the European Union (c) The authors This report is licensed under the Creative Commons Attribution International license Versions Date Comment Responsible Approved First Draft H. Flores/F. Schaafsma 12/12/2025 Formatting N. Van den Steen Table of Contents 1 Description of sampling gear .......................................................................................................... 4 2 Sampling gear deployment .............................................................................................................. 5 3 Sample sorting-collection-preservation procedure ............................................................... 6 4 Annex ........................................................................................................................................................ 6 1 Description of sampling gear The CCAMLR Working Groups recommended the use of a standard type of net to avoid potential variation in catchability and selectivity of nets. The most appropriate type of net presently available is the RMT8+1 (Rectangular Midwater Trawl ; Baker et al. 1973). It was agreed at CCAMLR WG-EMM-99 that this net shall be used as the standard net for target and random hauls. Alternative gear, such as an equivalent IKMT type of net of 8 to 10 m2 mouth opening, shall only be used if the RMT net is lost or damaged to such a degree that it cannot be repaired. The net has a mesh size of 3 to 4 mm. The net shall be equipped with a flowmeter to estimate the filtered water volume as accurately as possible, and a real-time time-depth-recorder (TDR) to follow the track of the net. Figure xx: The multi-RMT hanging from the A-frame, ready to be deployed (left) (©Fokje Schaafsma). 2 Sampling gear deployment Sampling strategy will depend on whether a multiple opening/closing RMT (MRMT 8+1) is used or a single RMT 8+1. The single RMT 8+1 down to 200 m is the minimum standard. If possible, however, the MRMT should be preferred to enable stratified sampling over a greater depth range. RMT 8+1 At each station a quantitative standard double oblique tow will be conducted from the surface down to 200 m and back to the surface (or to within 10 m of the bottom at stations shallower than 200m). During the hauls a constant ship's speed of 2.5 ± 0.5 knots is mandatory. It is recommended to maintain a wire speed of 0.7 to 0.8 m/sec (42 to 48 m/min) during paying out and of 0.3 m/sec (18 m/min) during hauling. The net mouth angle is remarkably constant during hauling within the speed ranges given above. When the net reaches maximum depth, the winch should be stopped for about 30 seconds to allow the net to stabilize before starting to retrieve the net. Usually, the net is hauled from the stern of the ship requiring to stop the propeller of the ship when the net reaches a depth of 15 to 20 m; this is to minimize the effects of the propeller action on the net operation and avoids damage of the samples. The total time of the net haul from surface to bottom to surface should be about 40 minutes. The use of a real-time TDR is essential to maintain a smooth net trajectory and control the maximum fishing depth. Factory-calibrated flowmeters must be used to give a measure of net speed during the haul as well as the total distance travelled. The dependence of mouth angle to the vertical speed of then net has been investigated for the RMT system. The formula of Pommeranz et al. (1982) should be used to calculate the filtered water volume for oblique hauls. (If horizontal hauls are used then the formulas of Roe et al., 1980, should be used). MRMT 8+1 missing – add in next version. At each station a quantitative standard oblique tow will be from600 m depth to the surface, opening nets at c. 600, 200, and 50 m depth. The maximum sampling depth is based on the penetration depth of the 38 kHz echosounder ensuring that the echosounder results, which is a non-invasive technique, can be validated. Ship’s speed, wire speed and max depth stop is similar to what is recommended for a regular RMT haul. 3 Sample sorting-collection-preservation procedure Process the catches from the RMT 1 and RMT 8 nets separately. Use a separate catch sheet for each net. Details on further sample processing can be found in the SOP for net sample processing. 4 Annex 1. Station protocol single RMT 2. Station protocol multiple RMT Annex 3: Explanatory example catch processing protocol