Discarded Tires Are ‘Ghost Fishing’ Hermit Crabs

Around 30 million metric tons worth of truck and car tires are thrown away each year. Most of these tires are recycled and used in fuel or in other ways, but millions of tires end up in landfills or being illegally dumped. Some of these tires end up in the oceans, where they can cause severe harm through negligence or unscrupulous intentions.
Although toxic chemicals and microplastic pollution from tires have been well documented, new research shows that their shape can pose a threat to wildlife. Tires can be deadly to crustaceans and hermit crabs if they end up in the oceans.

Today's study in Royal Society Open Science published its findings. It found that hermit crabs, who are known to live in discarded shells and climb into tires to seek shelter or food, eventually become trapped within the tire's interior. Researchers found that more than 1,200 hermits were trapped in six tires on the seafloor.

Atsushi Sogabe (an ecologist at Hirosaki University, Japan) is the study's principal author. He writes via email that he was inspired to conduct this research by his 2012 study of pipefish in Japan's Mutsu bay. On a research dive, Sogabe encountered a tire stuffed with shells on the seafloor. Sogabe discovered that some of the shells contained hermit crabs. He suspected that the tire's unique shape was similar to ghost fishing. In this case, lost fishing gear like nets and crab traps continue to capture sea life, but are never recovered.

Sogabe and his colleagues set up two experiments to see if hermit crabs could not find their way out from a tire after they had ventured inside. Sogabe and his coauthor set up six passenger car tires on the seafloor using tent spikes in 25 feet of water. To closely replicate tires that have been in the marine environment for a long time, the team allowed the tires to sit in the brine for approximately a year. Researchers also made sure to rescue any sea creatures from the tires during this period. Sogabe and his coauthor then swam to the tires every month and counted all the hermit crabs captured. The researchers released the animals after each visit from their rubber-walled cages.

Over the twelve months Sogabe and his coauthor spent watching them, the tires collected a total 1,278 hermits crabs. The highest number was March, when 246 hermit crabs were found trapped by the team. The researchers intervened and almost all the animals would have died inside the tires, it seems.

The lab conducted the second experiment. It was intended to evaluate hermit crabs' ability to escape from a standard car tire. Researchers dropped a tire into a large aquarium. They then released ten groups of hermit crabs, one inside and one outside. It took them 18 hours to work out the results. From 120 hermit crabs of two species, only 19 were able to crawl into the tire's interior.

The researchers found that submerged tires are a problem for hermit crabs and that marine pollution can have serious consequences for many ecosystems.

Past research has shown that hermit crabs are susceptible to the temptation to crawl inside shabby looking trash. In 2020, a study published in the Journal of Hazardous Materials showed that more than half a million hermits were trapped by plastic debris washed up on three islands. The study revealed a disturbing twist to the story: the plastic tombs' stench may attract more victims.

Because they are attracted by the scent of their dead, hermit crabs will be drawn to the shells that have just been re-sold. Once their fellow hermit crabs have died in a rubber tire or plastic bottle, the new crop of hermits may be tempted to find new real estate.

Ingrid Giskes is the Ocean Conservancy's Ghost Gear Initiative Director. She says this creates a dangerous parallel to what can happen with abandoned lobster or crab traps. Giskes says that it becomes a vicious circle where an empty trap becomes baited and continues to go on and on. Tires are so strong and durable that they can last for many decades.

There is no evidence that tires are causing problems for any of the 800 species of hermit crabs. However, if they are found in areas where tires and other forms are more common, this could have serious consequences for local ecosystems. Hermit crabs play an essential role as scavengers, searching the seafloor and intertidal zones for food that larger species might have missed. They also keep the environment clean. Because of their importance as food sources for other animals, many of the smaller hermit crab species are more closely related than lobsters.

Sogabe says that while the environmental problems found in this study are not as severe as global warming or ocean pollution due to microplastics, they can be significant. This is an example of how casual behavior can have a devastating impact on wildlife.

Sogabe believes future research on the topic may seek to narrow the scope of the problem and assess how many tires end-up in the oceans around the world. This will help determine where they could be dangerous for wildlife like hermit crabs.

Jennifer Lavers, a marine ecotoxicologist from the University of Tasmania, is the lead author of the 2020 paper. It highlighted the dangers of hermits getting stuck in plastic pollution. When you add them up to the global scale, the mortality that our paper calculated and this paper suggest are not small numbers. These numbers could rise further as plastic and tire production continue to increase.