Australasian Science Magazine

By Vanessa Pirotta

Road ecology is being applied to shipping routes to stop marine giants from becoming “roadkill”.

More than 80% of the world’s merchandise is transported by sea, but this comes at a cost to marine wildlife. Ships introduce oil and chemical pollution into the marine environment, emit greenhouse gases and other wastes, as well as noise pollution from ship engines.

Whales, basking sharks and whale sharks share similar traits that make them vulnerable to shipping activity. This includes their large body size, as well as time spent at the surface breathing (whales), feeding (some whales and sharks) and basking (sharks). They are also capable of long-range ocean movements that can cross many shipping routes.

We need to better understand how ships interact with these marine giants, many of which play important ecological roles within the marine environment. For example, whales are capable of moving nutrients and biomass through the ocean when their carcases fall to the bottom of the sea and via their bodily excretions.

While we have documented evidence of shipping impacts with some species, we know very little about impacts with others. To help better understand this knowledge gap, my colleagues and I have turned to the terrestrial world and sought help from ecologists who are studying the impacts of roads on the environment.

In a novel merging of disciplines, we applied road ecology to help better understand a number of impacts arising from shipping routes. From this we created a framework using known terrestrial road impacts to assess the ecological consequences of shipping on marine giants.

This resulted in the identification of four key road impacts used within the framework: physical disturbances, modification of animal behaviour, chemical pollution, and shipping lanes acting as fragmenting features.

Just like the roadkill we see on terrestrial roads, whales and sharks can also become “marine roadkill”. Ship strike is when a ship unintentionally collides with a marine giant, and is most commonly documented with large whales. For some species, such as the North Atlantic right whale, ship strike is one of many factors directly responsible for limiting population recovery post-whaling.

However, for most marine giants, the prevalence of ship strike is largely undocumented. Reasons contributing to this data gap include underreporting and species that are remote, rare or have vast ocean movements.

To complicate matters further, unlike terrestrial roads, shipping routes are featureless and only visible due to the presence of ships. This makes understanding how marine giants respond to the presence of shipping challenging. For example, whales use sound as their main form of communication, and this may be impacted by shipping noise. The sound produced by ships may deter whales from marine roads and impact their ability to communicate, while others may become habituated to the sound may not alter their behaviour.

Using terrestrial road ecology, we suggest managing shipping noise at the source (the ship) and beyond, as sound is capable of extending up to 10 km away from the ship. We call these areas “transition zones”, which provide a buffer for protecting marine giants from ship noise beyond the shipping route. This can also be applied to help understanding the movement of chemical pollution, such as oils, within the marine environment.

Now, more than ever, we must continue to consider shipping impacts upon marine giants, especially as the global shipping industry continues to grow while whale populations recover post-whaling. We must also consider the role of climate change in creating new shipping routes due to the decline in sea-ice in areas such as the Arctic, opening up once unnavigable areas and exposing some marine giants to shipping impacts for the first time.

Action needs to be a collaborative effort to ensure the protection of our marine giants, including help from the global shipping industry, International Maritime Organisation, scientists and marine conservationists. Implementing new technologies such as satellite tracking devices for whales and sharks, as well as automatic ship identification data, may provide further insights into the movements of both ships and marine giants.