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Ship traffic connects Antarctica’s fragile coasts to worldwide ecosystems

Significance Ship movements related to fishing, tourism, research, and supply expose the Antarctic continent to human impacts. Until now, only rough estimates or industry-specific information have been available to inform evidence-based policy to mitigate the introduction of nonnative marine species. Antarctica’s Southern Ocean supports a unique biota and represents the only global marine region without any known biological invasions. However, climate change is removing physiological barriers to potential invasive nonnative species and increasing ship activities are raising propagule pressure. The successful conservation of iconic Antarctic species and environments relies on addressing both climate change and direct, localized human impact. We have identified high-risk areas for introduced species and provide essential data that will underpin better evidence-based management in the region.


Supplementary Information Text Overview of Antarctic-going vessels
The network created by the movements of ships that visit Antarctica spreads right across the world. Ships that visited the Southern Ocean (south of -60) from 2014-2018, visited 1581 different ports outside the Southern Ocean and 126 within it. Our data show 255 ships visited the Southern Ocean (south of -60°) from 2014 to 2018, approximately 140 ships annually (Fig. S4). Although vessels used for fishing, research and tourism are well documented through the organisations that manage fisheries (Commission for the Conservation of Antarctic Marine Living Resources -CCAMLR (1)), national operations (Council of Managers of National Antarctic Programs -COMNAP (2)) and tourism, (International Association of Antarctica Tour Operators -IAATO (3)), we find that only 7% of supply vessels that visited the Southern Ocean from 2014-2015 were recorded in lists published by these organisations (Table S3).
Since data on sailing or many private vessels are not available through LLI, our annual ship numbers are in line with previous estimates (4). Previous estimates suggested that approximately 180 ships visit Antarctica each year, split almost evenly into research, fishing and tourism activity (4). At 29%, supply vessels form a substantial, and likely underestimated, proportion of ships visiting Antarctica (Fig. S4). Moreover, 56% of ships visited in only one or two of the 5 years studied (Table S4).
The sum of nodes from activity type networks (Table S5) (1839) indicates that there are 966 instances of a node appearing in at least two activity type networks. Tourism has 1284 nodes, much higher than any other activity type, meaning that tourism alone contributes at least 457 unique ports to the network. The range of species that could be introduced by tourism may be greater than for other activity types. In contrast, the fishing vessel network, is more dense than other networks, indicating that these ships re-visit the same ports over and over, rather than travelling between many ports.

Detection of known ships in satellite data
Of the 255 ships that passed the six stages of QC, 109 were not listed by IAATO (3), COMNAP (5) or CCAMLR (1) (Table S3). Thus, 43% of vessels that visit the Southern Ocean, were 'unknown' vessels, whose activity in the region is not readily available and were not included in previous estimates (4). However, it does not necessarily mean that that these vessels were unauthorised to visit, since Treaty Parties can authorise vessel visits without requiring the vessel to be listed with IAATO, COMNAP or CCAMLR.
However, there are also ships that are present in those lists that are not present in the satellite AIS data. The lists available through IAATO and COMNAP are not produced for specific years or seasons, therefore there may be some ships on those lists that did not intend to visit during the period in question. Any ships on those lists that were not built or operational during 2014-2018 were removed from the comparison. CCAMLR licenses fishing vessels for seasons that overlap calendar years, thus some vessels licensed for 2013/14 or 2018/19 might not been active during the 2014-2018 calendar years and would not be expected to be observed in the satellite AIS data. In addition, the CCAMLR area is greater than the Antarctic Treaty Area. It is divided into Areas and sub-Areas, some of which are entirely north of -60° and others that are partially south of -60º. Any vessels that were only licensed for areas north of -60° were removed from the comparison (after first checking that they were also not observed south of -60°). Vessels licensed for areas that were largely north of -60° but extended south of -60 were included in the comparison, but it is possible that the vessels did not travel south of -60° during their course of activity.
CCAMLR licensed 75 ships to fish within the CCAMLR area for the seasons 2013/14 to 2018/19. Of those, nine ships were not licensed to fish in areas south of -60° and were not observed south of -60° in the LLI data. 10 ships of the remaining 66 were not present in the LLI data. 80% of licensed fishing vessels were present in fishing vessels observed in the satellite observation data.
IAATO had at least 73 member vessels from 2014-2018. Of those, 23 were sailing vessels that are not in the LLI data. 50 IAATO member vessels were in the LLI data. Therefore 69% known IAATO member vessels are present in the satellite AIS data. Given the regulations on IMO numbers and AIS requirements, the lack of sailing vessels in the AIS data is expected. In addition, non-IAATO vessels authorised by a Treaty party were captured in previous estimates (4). 7 of 45 (15%) ships on the COMNAP list are not in the LLI data (85% of ships are present). However, this does not necessarily mean that the ships visited and were not observed, rather that national operators indicated that they intend to use these ships for their Antarctic operations.

Accuracy of Satellite coverage
Visits to Maxwell Bay, Pig Rock and Potter Cover in the port network (all in close proximity to the Fildes Peninsula on King George Island, South Shetland Islands) (Fig. 3), were compared to data on ship visits (name of ship, date, time, and duration of stay) collected by researchers studying seabirds and seals. The researchers were stationed at a field site on the Fildes Peninsula for up to three months during summer from 2013 onwards, from which they could observe ships in the bay and verify observations with radio activity. Some ships may have been missed if far away or when visibility was poor. Data were shared by Christina Braun, University of Jena, Germany.
For the overlapping periods, the satellite AIS data used to generate the port-to-port network captured 59% of visits to Maxwell Bay. 49% of visits were captured by both satellite AIS and researcher observations, 41% were captured only by researcher observations and 10% of visits were only found in satellite AIS data. Most observations present only in the researcher observations were from military vessels or yachts that are not present in the LLI data because they do not have IMO numbers. A small proportion of observations detected only by researchers were for ships that are present in the satellite AIS data.

Temporal and seasonal activity around Antarctica
The number of ships active in the Antarctic region (south of -60°) is highly seasonal, but consistent from year to year (Fig. S5). Tourism activity has a more distinct seasonal profile than the other activity types, operating only from September to April, and primarily from November to March, (Fig.  S5). All activity is lowest from August to October, coinciding with the greatest sea-ice extent in September. Activity is highest in January (fishing, tourism, research), February (supply) or March (other). Fishing and supply continue at moderate levels until May-June. Research activity is very low from May to October.
Each year saw more tourist ships visit Antarctica than other activity types (Fig. S4). Although, there may be a modest increase in tourism, fishing and research vessels over the 5-year study period ( Fig. S4) our data do not conclusively show that the overall number of ships visiting Antarctica each year is increasing, although other measures of impact, for example number of visitors, could have risen (4)). Supply ships had a peak in 2015, perhaps due to the adoption of the polar code in 2016 which introduced more stringent regulations for ships active in the polar regions (6).

Figure SD:
The port-to-port traffic network of ships that visited Antarctica from ijkl-ijkm inclusive, grouped by activity type: a Fishing, b Tourism, c Research, d Supply and e Other. Fishing vessels visit relatively few worldwide ports and tourist ships visit many ports worldwide, but visit few areas of Antarctica. Research vessels visit more Antarctic locations than other activity types, using many ports to access Antarctica. Supply vessels visit many worldwide ports but have fewer Antarctic voyages. For all activity types except other, the most important hub ports are in southern South America. Lines represent voyages between locations, darker lines indicating more journeys, but lines do not reflect the path travelled. For example, voyages across the pacific are represented by lines crossing over continents and the Atlantic Ocean. Circle color indicates the number of visits. Circle size represents Eigenvector centrality, the relative importance of ports within the network based on their connectivity to other highly ranked ports.

Figure SG:
Monthly activity of ships that visited the Southern Ocean (south of -vj°) from ijkl-ijkm inclusive. Antarctic ship activity is highly seasonal but consistent between years (a). Different activity types, while all more active in the summer months, show some variation (b). Tourism does not operate at all from April to September, but fishing, supply and research ships are active in low numbers over the autumn and winter months.