CPR – Industry and Science working together

Figure 1. The Discovery held up in congested pack ice off MacRobertson Land Antarctica. Dundee Heritage Trust

How an Industry/Science partnership using steam age technology is improving our monitoring and understanding of the Southern Ocean.

This story begins with Sir Alister Hardy (1896-1985) who invented the Continuous Plankton Recorder (CPR).

Sir Alister was the son of an architect, and following war service went to Oxford in 1919, studying zoology, graduating with distinction. He was taken on as zoologist on the RRS Discovery voyage to the Antarctic between 19251927 and it was during this voyage he invented the Continuous Plankton Recorder (CPR). His groundbreaking research into plankton and his design of the CPR is still the basis for much of the global plankton work carried out today.

Figure 2. The internal workings of the Continuous Plankton Recorder (CPR). (after New Zealand Aquatic Environment and Biodiversity Report No. 257 – Fisheries New Zealand)

Full credit to Sir Alister, the CPR used by us in this project today is still largely based on his original model, with some minor modifications to allow for the more extreme sea conditions in the Southern Ocean. No batteries, no apps, no digital technology only brass gears, steel wires, a bit of preservative and a timeless clever design. Sir Alister was knighted in 1957 to recognise his groundbreaking work in marine biology.

A CPR survey was implemented in 1931 in the North Sea and North Atlantic and is still carried out today. This is one of the longest-running marine biological monitoring programs in the world and has identified and continues to monitor major changes in marine ecosystems.

How does the CPR work? The unit is towed horizontally about 10 m down from the surface and around 100 m behind the boat. As it is pulled along, water enters a small aperture at the front of the CPR body and then passes through a 270 µm filtering collecting silk (See figure 2). An external propeller advances the silk at a rate of around a cm for each nautical mile towed independent of the speed of the ship. This ‘filtering silk’ then a ‘covering’ silk, and any plankton caught are trapped between the two layers. These sandwiched silks are then rolled storage where a supply of buffered formaldehyde preserves the sample. At the end of each tow lasting around 420 nautical miles the silks are recovered, labelled and stored in formaldehyde At this point new silks can be inserted, and another tow commenced. On return to port, the silks are removed from the mechanism and divided into sections representing 10 nautical miles (19 km) of tow.

In 2008 an agreement was made between government (now MPI), Sanford Limited, and NIWA to use Sanford science representatives on the longline vessel San Aotea II to carry out CPR transects on north and south transits between New Zealand and the Ross Sea toothfish fishing grounds.

Figure 3. CPR about to deployed in the Southern Ocean from San Aotea II

The initial aim of this project was to map quantitative changes in the distribution of epipelagic plankton, including phytoplankton, zooplankton and euphausiid (krill) life stages, both within New Zealand’s EEZ and the Ross Sea, Antarctica. Extending from just south of the port of Timaru to the Ross Sea, the exact route has varied over seasons due to the fishing locations chosen and the seasonal distribution and concentration of sea ice in the south. Since 2008 about 30 north and south transits have been carried out by San Aotea II.

Information provided from the 16 years of this collaborative research has provided excellent data to support various analyses such as mapping the concentrations of chlorophyll-a in the Southern Ocean, general information on the broad spatial and temporal patterns of zooplankton abundances associated with environmental changes due to climate change, and quantification of micro plastics in the marine environment.

NIWA trains Sanford vessel scientific representatives to load the internal cassettes with new silks, replace these in the body of the CPR at about 410 nm intervals, deploy and retrieve the CPR, label and preserve the samples silks, and carry out all associated recording of location and time. NIWA carries out the post-trip analyses on the collected material. General support for CPR equipment and training is also provided by Graham Hosie and John Kitchener (Australian Antarctic Division, Hobart, Australia) and The Marine Biological Association CPR Survey).

This is now one of the longer-running time series CPR projects from the southern hemisphere/ Antarctica and continues to provide consistent, and increasingly useful trend information.

This project is a great example of industry support and cooperation (Sanford Limited) with government and research providers closing information gaps and provide an alternative and useful addition to more limited research vessel activities. This is increasingly important in times of potential changes in the environment.

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