Four steps to curb ‘ocean roadkill’

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Humanity and some of the world’s most charismatic wildlife are on a collision course in the oceans.

The world’s merchant fleet — from oil tankers to bulk cargo carriers and container ships — has doubled in size in just 16 years to more than 100,000 vessels, according to United Nations figures (see ‘A fast-growing fleet’). Between 2014 and 2050, shipping traffic is expected to rise by up to 1,200%1.

These numbers, combined with data on where shipping networks overlap with the movements and aggregations of marine animals2,3, together with assessments of the effects of ship strikes on certain marine species, present an increasingly alarming picture. They suggest that ship strikes could be helping to drive the population decline of many animals, leading to profound effects throughout their ecosystems, for instance by altering biogeochemical fluxes4.

Source: UNCTAD

Yet compared with other threats to marine biodiversity, such as climate change and pollution, the problem of ship strikes harming wildlife is tractable. Various technologies and approaches are increasingly enabling surveillance of both ships and wildlife. Global regulation of the shipping industry has already been established to limit greenhouse-gas emissions. And various schemes to reduce strikes have proved effective in some locations for certain species.

What’s needed now are four changes. First, researchers require better data on where, when, how often and for which species strikes are occurring. Second, there must be greater engagement with the problem, both from the shipping industry and the public. Third, regulations should be brought in to either reduce ship speed in certain areas or reroute vessels; and finally, there must be monitoring of adherence to such restrictions. With these changes, there is no reason why this problem cannot be addressed.

Tip of the iceberg

Collisions between ships and ocean animals are hard to quantify because they are not systematically recorded, and can go unnoticed when large vessels are involved. Carcasses can sink before they are observed.

Numerous lethal strikes have been documented worldwide in the past 100 years or so, often by scientists using eyewitness accounts or by direct observations of floating, dead animals2,3. Researchers have been warning of the impacts of global shipping on whales for nearly two decades5. And for some species, research has established the importance of ship strikes relative to other threats. A 2019 study, for instance, showed that, alongside entanglement in fishing gear, ship strikes are a leading cause of human-induced mortality for the critically endangered North Atlantic right whale (Eubalaena glacialis)6.

An acoustic monitoring buoy.Credit: Woods Hole Oceanographic Institution

By collating information dating back to 1877 on what species have been struck by vessels, a 2020 study identified more than 75 marine species as being at risk of harm from strikes2. The marine megafauna — whales, sharks, sea turtles and other organisms with a body mass of 45 kilograms or more — top the list. These ocean giants spend most of their lives at the surface3, travel hundreds or thousands of kilometres across ocean basins and often aggregate in coastal and continental-shelf areas7.

The list includes some of the most endangered animals: 60 are on the International Union for Conservation of Nature’s Red List of Threatened Species2. More than one-third of those listed are threatened with extinction. For the other 15, there are insufficient data to make an assessment.

Studies on ship strikes so far, however, are not comprehensive and have drawn on data collected only from particular areas and only for some species. According to conservative estimates based on deaths of three whale species in four US study sites, for example, ships kill more than 80 whales a year in an area measuring roughly 800,000 square kilometres8. Yet for other species, data on the number of deaths and the location of collisions are missing. Reports of strikes tend to focus on a few species that are most likely to be seen floating when dead, such as whales, dolphins and turtles. But the majority of marine animals, and all cartilaginous fishes (sharks, rays, skates and so on), sink when dead and so will not be observed2.

A 2022 study co-authored by two of us (F.C.W. and D.W.S.) attempted to assess the global impact of collisions on whale sharks (Rhincodon typus), a species that sinks quickly when dead3. The findings are concerning. Satellite data that tracked the relative positions of whale sharks and vessels show that 92% of the species’ use of horizontal space and nearly 50% of its vertical space use overlaps with shipping routes. Strikes could explain why the population is continuing to decline even though mortality caused by fishing has been reduced.

In short, various lines of evidence indicate that existing records of ship strikes — and the estimates made so far of the impact of collisions on marine life — represent the tip of the iceberg for current and future harms of the shipping industry to marine biodiversity.

Data on demand

Fortunately, the tools and key players needed to collect and analyse data across ecosystems and jurisdictional borders — and to develop mitigation strategies — already exist.

Various international projects are already collating and distributing data on where animals are and how they move through the ocean. These include platforms that rely on surveys, such as the Ocean Biodiversity Information System; animal-tracking databases such as Movebank; and tools that predict animal distributions on the basis of sightings and assessments of habitat suitability, such as AquaMaps.

Likewise, shipping information can be obtained from providers of Automatic Identification System data, which use satellites to track vessels, as well as from ocean-monitoring initiatives such as Global Fishing Watch and from the US National Oceanic and Atmospheric Administration (NOAA).

A shortfin mako shark (Isurus oxyrinchus) with satellite tags in the Pacific Ocean.Credit: Mark Conlin/Alamy

Using such data, whale experts and other researchers have already started to pinpoint high-risk areas2,3 (see Supplementary information). Our work on whale sharks showed that one is the Strait of Hormuz between the United Arab Emirates and Iran, through which about one-third of global maritime-traded oil passes each year (see

For many species, this information is not yet available. Also, data collection is often patchy and disparate, with animals being tracked only in part of their range, and various data-gathering approaches being used in different areas.

Governments, industry and philanthropic and other organizations can help to fill the gaps by bolstering pre-existing projects. Various mobile-phone app and web-based initiatives are leading the way with technology-powered mapping and analysis. For instance, the Whale Safe tool uses various measures, including public whale sightings, to help establish voluntary speed restrictions and other actions to reduce the risk of strikes. The use of low-Earth-orbit satellites to monitor large marine animals from space — currently an untapped technique — could provide researchers and other stakeholders with near-real-time, actionable data for high-risk areas9.

But efforts must be scaled up, with those involved in local and regional projects facilitating the establishment of similar initiatives in other parts of the world, particularly in the global south. Existing efforts to connect projects and partners associated with the ocean will be key. Since 2021, for instance, the United Nations Decade of Ocean Science for Sustainable Development programme has been connecting people and organizations concerned with the role of kelp forests and seagrass beds in storing carbon, among many other issues.

Increased engagement

In the past few years, it has become increasingly common for commercial shipping companies to disclose their environmental, social and governance goals in publicly available sustainability reports. Although nine of the ten largest shipping companies address whale strikes as an area of concern in their reports, the degree to which companies take action on this issue varies widely. Also, to our knowledge, none of these sustainability reports explicitly mentions megafauna other than whales.

In 2007, the International Whaling Commission launched a long-term initiative to collect and analyse information about reported whale strikes: the Global Ship Strikes Database. With greater engagement from shipping companies, port authorities and industry partners, a centralized database of strikes could be built for all affected species. As well as protecting marine wildlife by helping ships to avoid collisions, such a database could bolster companies’ reputations in an increasingly eco-conscious world, and lessen disruptions to shipping operations.

Hong Kong’s container terminal is one of the largest in the world.Credit: xPACIFICA/Redux/eyevine

Currently, the International Convention for the Safety of Life at Sea (SOLAS), a treaty that ensures ships registered by signatory states comply with minimum safety standards, requires that all ships engaged in international voyages keep an on-board record of navigational activities and incidents relevant to safety. Adding wildlife collisions and near misses to this reporting could enable information to be collected in a comprehensive ship-strikes database. Another measure could require particular ships to have marine megafauna observers on board. (This already happens on vessels conducting seismic surveys, for example, to ensure that the noise from underwater soundings is minimized when whales are nearby.) On the rare occasions on which animals remain lodged on a ship’s bow, strikes could even be recorded by port authorities.

Ways to record ship strikes without direct human involvement are being developed, including forward-facing and thermal-imaging cameras, infrared and thermal sensors and underwater echo sounders to image animals. Technology developed by the Woods Hole Oceanographic Institution in Massachusetts uses a camera the size of a shoebox and an artificial-intelligence (AI) algorithm to help ships detect and avoid whales10. (The algorithm is trained to identify whether a whale is present; if so, the program sends a signal to the ship’s operator so they can slow down or change course.) Also, the shipping industry is increasingly using advanced autopilot systems based on AI and deep learning11. In principle, hazard-detection systems on autonomous vessels could be trained to identify marine megafauna, log incidents and implement any necessary evasive manoeuvres.

Conventions and treaties that are already in place to increase industry and public engagement in ocean-environment issues could help with all this. But instruments such as the Biodiversity Beyond National Jurisdiction treaty (a framework adopted earlier this year to tackle biodiversity loss on the high seas) must explicitly address the issue of ship strikes. Currently, there is no mention of this in the treaty.

Shipping regulations

The best way to reduce strikes is to separate ships from wildlife. The International Maritime Organization (IMO) is a specialized UN agency responsible for worldwide shipping regulations. Through SOLAS, the IMO can reroute ship traffic to avoid collisions with a floating object or to ensure that areas crucial for some species’ feeding or reproduction at particular times of year are avoided.

Permanent or seasonal traffic diversions around wildlife areas have proved hugely effective2. For whales, even minor routing changes in high-risk areas have led to substantial reductions in strikes. For instance, in the Bay of Fundy off Canada, moving a shipping route eastwards by just 4 nautical miles (7.4 km) in 2003 reduced the risk of vessels colliding with North Atlantic right whales by 90%12.

A whale shark (Rhincodon typus) thought to have been scarred in a collision with a vessel.Credit: Claudio Contreras/Nature Picture Library

Several studies and reports show that, in places where ships cannot be rerouted, speed reductions can lower the risk and the lethality of a strike2. In 2008, voluntary and mandatory speed limits of 10 knots (18.5 km per hour) were applied in certain areas along the US east coast. In the first 5 years after implementation, there were no records of ships striking North Atlantic right whales either inside or within 45 nautical miles of these areas13. Studies incorporating emissions show that speed restrictions can bring other benefits. In a 2019 study, decreasing speeds by as little as 10% lowered the risk of ships striking whales by 50%, reduced underwater noise by 40% and cut greenhouse-gas emissions by 13%14.

Despite the evidence that rerouting and speed reductions mitigate ‘ocean roadkill’, restrictions on ship routes and speeds remain disparate and uncoordinated, just like data collection on marine animals. A global, IMO-mediated treaty mandating maximum average speeds — and rerouting to ensure ships avoid areas of high collision risk — could be one of the easiest ways to protect wildlife from ship strikes. In fact, regulations introduced this year to ameliorate the effects of climate change from shipping, such as the IMO 2023 Energy Efficiency Existing Ship Index and the Carbon Intensity Indicator, already stipulate lower speeds for certain vessels.

A cloud-based, open-data portal could facilitate the establishment of up-to-date, dynamic policies by integrating data on animal and ship movements, risk maps, geo-referenced strike reports, current spatial protections and relevant maritime features into a single mapping resource. This would be similar to HUBOcean, which brings diverse data sources together on one platform to enable scientific collaboration, industry transparency and regulation. Crucially, data could be made available to all stakeholders, from government agencies and non-governmental organizations to academic researchers and industry partners.

Monitoring adherence

Once regulatory changes have been relayed to industry, adherence to speed and route restrictions could be monitored at a national level using data from Automatic Identification Systems. Ship owners, shipping companies and port authorities could also help to ensure regulatory compliance. Financial penalties could be used to discourage speeding or encroachment in no-go zones. In principle, subsidies, tax breaks and other forms of governmental financial support aimed at environmental objectives could be used to reduce ship strikes on marine megafauna.

Because governments are unlikely to act without sufficient public pressure, a global ‘wildlife-safe’ shipping eco-certification scheme could be crucial. Similar to NOAA’s ‘dolphin-safe’ tuna-can labels — which aim to signal compliance with US laws and regulations around tuna fishing operations — this would help to increase consumer awareness of the problem and enable informed choices. Scaling up the success of voluntary certification programmes, such as Friend of the Sea’s Whale-Safe label, alongside its certification of seafood from sustainable fisheries and aquaculture, would greatly increase the visibility of this issue.

Loss of the ocean’s largest animals will have major unforeseen consequences for the health of the seas. Making ship strikes a higher priority globally is one immediately achievable way to help to conserve the world’s most vulnerable and iconic marine species.

Source: Ecology -

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