Continuous Plankton Recorder

A scientist prepares the recorder to be dropped overboard
Setting up continuous plankton recorder on trawl deck of Aurora Australis (Photo: Wayne Papps)
Expeditioner connects the CPR to the cableThe metal casing is hung out on a winch over the back of the ship.

The Continuous Plankton Recorder (CPR) is one of the most successful and longest running marine monitoring devices.

The concept of the CPR was first developed by marine biologist Sir Alister Hardy in 1922, while aboard the British Ministry of Agriculture and Fisheries research ship, George Bligh. His ideas bore fruit and the first CPR was built and perfected during his time as zoologist on the RRS Discovery, in Antarctic waters between 1925 and 1927. This was known as the Type I CPR. Later the more compact Type II CPR set the design standard and has been used for over 70 years in the North Sea and North Atlantic CPR survey, the world longest running marine biological survey.

The Australian Antarctic Division's CPR units were obtained in 1990 from the Sir Alister Hardy Foundation, and trialed on the Aurora Australis during the ship's first voyage to Heard Island. Due to constant ice damage during retrieval the Australian Antarctic Division instrument workshop designed the Type II Mark V CRP. Two main departures from the original design were to use marine grade stainless steel instead of phosphor bronze, and to streamline the shape further.

Below is a description of how the CPR works by the AAD's Dr Graeme Hosie

It is a self-contained automatic sampler towed behind the ship at normal ship speed and can operate in nearly all sea conditions. As the CPR is towed along, water and zooplankton enter a small 1.25 x 1.25 cm aperture in the nose cone, which then expands into a wider collecting tunnel, slowing down the water flow. The plankton are then trapped between two bands of 270 µm mesh silk (6 m long x 15 cm wide) loaded in a removable cassette. The silk and plankton 'sandwich' is wound onto a take-up spool inside a formalin preserving chamber, all driven by passing water turning an external propeller. Regardless of the speed of the vessel, the sheets of silk are advanced at a fixed rate of 1 cm per nautical mile travelled. Each tow represents a 450 nautical mile track of continuous sampling. Back in the laboratory, each set of silks is unrolled and cut into sections representing five nautical mile samples. Plankton are then identified by microscope and counted.