Greatest distance sampled by a marine survey

The Continuous Plankton Recorder (CPR) Survey is one of the world’s longest-running marine science projects. Established in 1931 by British marine biologist Sir Alister Hardy, it was originally intended to help understand how plankton influenced herring numbers, however its scope today goes much further than just fishery data. Coordinated by the Marine Biological Association (based in Plymouth, Devon, UK) the CPR Survey uses towed marine samplers to provide a comprehensive overview of the current state and historic trends of plankton, as well as valuable insights into aspects such as climate change, marine litter (including a crucial role in the recent recognition of microplastic), pathogens and ocean acidification. By 31 December 2020, the survey had studied 7,063,622 nautical miles (13,081,828 km; 8,128,671 mi) of ocean – equivalent to 326 circumnavigations of the world – over the course of its almost-90-year history. The greatest distance sampled in a single year was 140,208 nautical miles (259,665 km; 161,348 mi), logged in 2014.

A Continuous Plankton Recorder (CPR) is a 1-m-long (3-ft 3-in) torpedo-shaped device containing an internal “cassette” to collect plankton samples. Towed behind ships, seawater enters the CPR and is filtered through a fine silk mesh which captures the plankton. A second layer of silk covers the first, forming a plankton “sandwich” before being preserved in formaldehyde. Each cassette covers 450 nautical miles (833 km; 518 mi) of ocean. Back at the lab, the silks are unwound and cut into samples ready for analysis using light microscopy. Each sample represents 10 nautical miles (18.5 km; 11.5 mi), approximately 3 m3 (100 cu ft) of seawater. Since 1931, the design of the CPR and subsequent analysis techniques have changed very little.

This long-running citizen-science project relies on volunteer merchant vessels and ships of opportunity towing CPRs on voyages they would already be making as part of their day-to-day business.

CPRs are regularly deployed in the North Sea, North Atlantic and North Pacific, however they have been towed in many locations around the world through collaborative projects. Several institutes globally have also adopted the CPR design to monitor plankton in their local waters.

Today the CPR Survey provides unparalleled information on the health of our oceans. This careful monitoring helps shed light on changes occurring at the base of the marine foodweb, which may affect the wider marine ecosystem. All CPR Survey data are freely available and used by scientists and policymakers around the world to support improved management and conservation of the marine environment.