Trawl Net Mounted Sea-Bird SBE 19plus V2 CTD – 180 Successful Deployments

With over 180 trawl mounted CTD deployments successfully completed by Dr Larry Hutchings (Ma-RE, UCT) using a Sea-Bird SBE 19plus V2 CTD system mounted in a Sea Technology Services ruggedized Trawl Net Instrument Casing, Sea Technology Services is pleased to announce the awarding of an order from Nautic for a duplicate of this system.

The Sea Technology Services ruggedized Trawl Net Instrument Casing has enabled the collection of high quality SBE-19plus V2 data during demersal trawling operations.

Dr Hutchings summarises:

“The CTD not only provides profiles of the water column during the start and end of the trawl (up to 10 nautical miles apart on some commercial trawls) but also a time series during the bottom time, where changes in temperature of up to a degree celcius have been observed. Hake are generally relatively sparsely distributed, with high catch rates signifying aggregations of some sort. This CTD may provide us with insights into some of the environmental reasons why hake aggregate, apart from spawning or feeding activities.

The CTD is deployed under all sorts of weather conditions, such as strong winds and rough seas, which can inhibit vertical deployment from a dedicated winch and davit system. There are a few processing issues as sample analysis depends on selection of a profiling mode or mooring mode and this deployment is a bit of both. In particular the loop edit processing step, designed for removing ships roll or a slow rate of descent is a bit confounded when the trawl net reaches the sea bed, so a mixed mode of processing is required.

The other sensitivity is relatively rough handling as the package goes down or comes up over the stern ramp and up the trawl deck. However some care by the crew and skipper/winch operator and some foam padding has cushioned many of the bumps and jolts which are inevitable in this mode of sampling. It also provides useful supplementary information on actual bottom contact time to complement the net sensing system in place. For research surveys, there is an additional bonus of a saving of expensive ship’s time, allowing extra trawl stations each day and reducing survey costs.”