Our findings are the first to confirm the expected significant increase in plastics in the open ocean since the 1990s7,14,15,16,17. We have presented a significant increase in macroplastics from 1957 to 2016 (Fig. 1), which agrees with the exponential increase in total plastic production worldwide3. It has been suggested that there may be a sink of plastic items within global oceans, which could have led to reduced estimates of sea surface plastics and have implications for plastic pollution7,17. Perhaps the reason we have been able to show the expected increase, is because the focus of this work has been on larger plastic items that entangle on the CPR. It should be noted that these larger plastics (macroplastics) break down under ultra-violet light and mechanical forces within the ocean, leading to smaller fragments forming microplastics20, therefore they have the potential to be a proxy for a wide-range of plastic sizes within the oceans.

There are very few historical records of oceanic plastic occurrence, in particular time series of macroplastics, with the most common reporting stemming from ingestion studies of seabirds and sea turtles3,5,11,21,22,23,24,25. In 1947 the earliest known reporting of entanglement was documented, when a herring gull was impeded by a piece of string5,26. However, it is uncertain if this string was made of plastic or natural fibres. In this study we have presented two early records of entanglement, one from 1957 when trawl twine was caught on the CPR and one in 1965 from plastic bag entanglement. The observations of trawl twine is synonymous with the widespread use of plastic for fishing practices in the 1950s as plastic became economical and more efficient to use than natural fibres5,6. Therefore although we cannot confirm that the twine was made from plastic, it is likely, as it was recorded in the late 1950s and was specified as trawl twine. The record of a plastic bag entangled on the CPR in 1965 is within the same decade as the first known recordings of plastic entanglement and ingestion by seabirds21,22,23, and marine turtles7,24,25, which were observed in the late 1960s.

The data presented in Fig. 2 demonstrate that macroplastic debris are found throughout the North Atlantic. More macroplastic entanglements occurred in high-density shipping route areas, than areas of the open ocean such as the eastern North Atlantic, this could be due to the increased presence of human activity6 introducing large plastic items to those areas (Fig. 2, and www.marinetraffic.com). Although the first record of man-made entanglement on the CPR in 1957 was recorded in Arctic waters (Fig. 2 and Supplementary Fig. 1), we do not find a significant increase in macroplastic entanglements (Supplementary Fig. 3e), this is due to an increased number of CPR tows in the last decade in Arctic waters and our normalisation method employed to remove sampling bias (see methods for normalisation method and Supplementary Fig. 2e). However, we do record a peak in macroplastic entanglement cases in Arctic waters between 2009–2011 (Supplementary Fig. 3e), which corresponds with a significant increase in macroplastics between 2002–2014 seen at two stations at the HAUSGARTEN observatory in the Arctic27. Although not a significant increase, there were more plastic entanglement cases reported during January and December than any other month, suggesting that winter conditions such as high winds, rainfall and river run-off, may have increased the amount of plastics within the oceans (Supplementary Fig. 4). This could partly explain the distribution of macroplastics seen in Fig. 2, where more entanglements have occurred near coastal and riverine input areas, such as the southern North Sea and the English Channel (Fig. 2 and Supplementary Fig. 4, perMANOVA p-value < 0.0519). These areas are also more likely to be impacted by anthropogenic pollution due to their close proximity to human populations6.

Macroplastic items such as line and string are more likely to cause entanglement due to their shape (Fig. 3 and Supplementary Fig. 5). Our findings suggest that man-made entanglement from fishing related gear has significantly increased in recent decades (Fig. 3 and Supplementary Fig. 4), and could be more likely in areas such as the North Sea than the open ocean of the North Atlantic, where higher occurrences of macroplastics were reported to be entangled on the CPR (Fig. 2 and Supplementary Fig. 4, perMANOVA p-value < 0.0519). Although very few recreational fisheries are monitored in the North Sea, and commercial fish landings have reduced overall since the 1970s, data from the ICES fisheries overview indicates that pelagic trawl/seine fishing gear landings have increased since 2003 to 2015 in the North Sea28. The North Sea has large seabird and seal populations, as well as cetaceans, that are likely to have encountered plastic items and are at increasingly higher risk of entanglement29,30.

As the global population continues to increase, plastic waste will continue to grow31. The realisation that plastics are ubiquitous, and that the consequent health impacts are yet to be fully understood, has increased the awareness surrounding plastics. Plastics are likely to be used as an indicator of marine health in environmental monitoring to drive policy (e.g. the Marine Strategy Framework Directive32). However, progression to reduce the inputs of plastic into the ocean is required7,33,34. There is a need for re-education, continued research and awareness campaigns, in order to drive action from the individual as well as large-scale decisions on waste-management and product design4,33,34,35. The use of ships-of-opportunity is an efficient (both in cost and time) way of covering vast areas, and should be utilised further to develop standardised and consistent strategies for monitoring plastic debris in the oceans7. The dataset presented here is an important historical record for the continued monitoring of plastics in the ocean, and confirms the importance of actions to reduce and improve plastic waste.