A plankton monitoring device towed behind commercial ships has accidentally created one of the longest records of floating plastic pollution in the North Atlantic with researchers finding a clear rise in plastic entanglements over six decades.
The Continuous Plankton Recorder, which filters seawater through silk mesh at about seven metres below the surface, has been towed across the North Atlantic since 1957. Between 1957 and 2016, it completed 16,725 tows covering more than 6.5 million nautical miles.
Researchers led by Clare Ostle of the Marine Biological Association examined decades of maintenance records originally created to document equipment failures. They identified 208 confirmed cases in which the recorder became entangled with man made plastic debris.
The first recorded incident occurred in 1957 off Iceland, when trawl twine became caught in the instrument. A plastic bag was recorded in 1965 off northwest Ireland.
Plastic encounters remained relatively uncommon for several decades but increased sharply from the 1990s onward. The research, published in Nature Communications in 2019, found that entanglement rates were roughly an order of magnitude higher from 2000 compared with the earlier baseline.
Fishing related debris, including nets, ropes, lines and fragments, became increasingly prominent in later records, particularly in the North Sea. Plastic bag entanglements, however, declined after 2000 even as overall macroplastic encounters continued to rise.
The dataset is valuable because the records were not originally created to monitor pollution. Technicians were simply documenting problems with an instrument, reducing the likelihood that the observations were influenced by expectations about plastic pollution.
However, the records do not measure the total amount of plastic in the ocean. They cover mainly surface waters along commercial shipping routes and cannot reveal pollution in deeper waters or areas outside those routes.
Researchers say the findings nevertheless provide important evidence of the long term increase in floating macroplastic pollution and demonstrate how decades old monitoring archives can reveal environmental changes that were never part of their original purpose.
The Continuous Plankton Recorder survey continues to operate today, using commercial vessels as “ships of opportunity” to monitor plankton and changing ocean conditions across the North Atlantic.