What are possible causes of loggerhead turtle biting swimmers?

With the aim of raising public awareness and clarifying possible causes of these unpleasant experiences, especially for individuals who have been bitten, in the following text, we will attempt to briefly explain the possible reasons for the bites and provide guidance on how to behave.

Authors:
Asst. Prof. Draško Holcer, PhD – Croatian Natural History Museum, Zagreb
Tina Belaj, DVM – Sea Turtle Rehabilitation Centre, Blue World Institute, Veli Lošinj
Assoc. Prof. Bojan Lazar, PhD – University of Primorska, Koper, Slovenia

In recent days, there have been reports in the media about swimmers being bitten by sea turtles. Numerous explanations for the bites have been circulated, and the media attention and various layman explanations have caused concern among individuals, especially in areas where such incidents have been recorded.

Loggerhead turtle (Carreta carreta)

Sea turtles mostly live as solitary individuals. The Adriatic Sea is predominantly inhabited by loggerhead turtles, for which the northern Adriatic is one of the main Mediterranean areas for feeding and hibernation. It is estimated that there are over 100,000 individuals of loggerhead turtles in the entire Adriatic region. This number includes various age groups of turtles – from small, sexually immature animals to adult individuals whose shells can be up to 120 cm in length. Most turtles primarily reside in the open sea, so they are usually not noticed by people. A smaller number of turtles approach the coast and enter the channels between our islands, making occasional encounters possible. Besides loggerheads, a small number of green turtles, which also inhabit the Mediterranean, and very rarely the leatherback turtles, which come to the Mediterranean Sea from the Atlantic Ocean, can be found.

The main Mediterranean nesting sites for loggerhead turtles are found in Greece, Turkey, and Cyprus. During the mating season, adult individuals migrate from their feeding areas to the nesting sites. The actual mating takes place in front of the nesting areas, and after fertilization, females come out on the beaches where they lay eggs in the sand in multiple sessions over a period of several months. Male sea turtles never leave the sea.

Although they mostly live solitarily, during the mating season, adult males gather in the nesting areas and can aggressively defend the territories they occupy while waiting for females to mate with. While sea turtles are not aggressive and do not pose a threat, there can be interactions and fights between males in the nesting areas as they establish dominance. These fights may involve biting opponents’ necks and flippers or attempting to keep the rival underwater, among other behaviors. Occasionally, males defending their established territories may also attack other larger “organisms,” including swimmers.

Due to the hard bony shell that protects the loggerhead turtle’s body, their mobility is not particularly high. Therefore, when attacked, the turtle can only defend itself in two ways: by trying to escape or, if that is not possible, by biting. Since loggerhead turtles feed on prey from the sea floor, such as mollusks, snails, crabs, sea urchins, and other invertebrates, they have exceptionally strong jaws to crush the shells of these organisms. Hence, depending on the size of the animal, injuries from a bite can be severe.

Loggerhead turtle (Carreta carreta)

During the last few days, there have been several reports of bites by loggerhead turtles in the vicinity of Slatine beach on Čiovo. As bites by sea turtles in the Adriatic are extremely rare, and there have been no significant incidents before, it was presumed that sea turtle might have bitten swimmers out of fear and self-defense, especially considering recent reports of intentional harassment of the animals. It is essential to note that the only known recorded case of loggerhead turtles biting multiple swimmers in the Adriatic occurred in the Bay of Kotor, as described by physicians from the General Hospital in Kotor in a scientific article published in the journal Acta medica Croatica (the scientific article is available at https://hrcak.srce.hr/file/319644). Similar “attacks” have been reported elsewhere, such as in Greece, and there are known cases where male turtles, driven by increased testosterone secretion during the mating season, have attempted to mate with swimmers.

The repeated incidents in recent days suggest other possible causes for the bites. An analysis of the recent events on Čiovo may indicate that the individual turtle has settled in the area in front of the beach and is defending it from intruders for some reason. While we described aggressive behavior by male turtles in nesting areas at the beginning of the text, no nesting of loggerhead turtles has been recorded in Croatia. However, in recent years (presumably due to the influence of global climate change, warming seas, and an increase in the number of loggerhead turtles in the Mediterranean), several nests of loggerhead turtles have been recorded in the Adriatic – in Albania and Italy. In 2021, a nest was found in Jesolo near Venice, which is the northernmost nest of loggerhead turtles ever recorded. During the mating season, male loggerhead turtles can travel between multiple geographically distant reproductive habitats. To ascertain whether a solitary male has “occupied” the area in front of the beach on Čiovo and is defending it while waiting for females, or if it is a temporary stay of an adult individual in this area, better photographs of this turtle are needed. Apart from the impact of possible extension of nesting habitats due to climate change and warming seas, the reason for this animal’s attack might also be related to its previous “experience” with humans. For example, it is known that solitary dolphins or dolphins that frequent areas where humans feed them can become extremely aggressive when they do not receive the expected food from swimmers. Animals that receive food from humans may stop actively hunting and become accustomed to being fed by people, so they associate all humans with the possibility of being fed. When they encounter people who do not offer them the expected food, they can become aggressive. Many other marine and terrestrial wildlife species behave similarly when humans feed them in the wild. That’s why we often emphasize that dolphins (and other marine animals) should not be fed in their natural habitat. Without proper marking (metal or plastic tags with a number and the name of the institution that issued the tags attached to the flippers), it is not possible to determine if this turtle has previously been in an area where it was in proximity to humans and received food from them, leading it to expect something similar now.

Harassment of loggerhead turtle in Petrčane is punishable by Law.

At the same time as the emergence of information about the bites, we received footage from a beach in Petrčane showing two men dragging a large loggerhead turtle into shallow waters. In the video, the turtle is seen struggling to free itself and attempting to bite the person holding it, confirming our previous statement that biting is the only defense mechanism of sea turtles. All species of sea turtles appearing in the Adriatic are strictly protected, and the behavior of these individuals clearly indicates a violation of the Nature Protection Act, as it involves hunting and maltreatment of a strictly protected species. The video has caused public outrage and condemnation, indicating a high awareness among citizens that marine organisms are not toys.

What can we do?

In the case of the turtle residing in the area of Slatina Beach on Čiovo, we urge swimmers to be cautious. When entering the sea, it would be desirable to pay attention to the presence of the turtle and, in case it approaches, to step back from the water. If possible, it would be beneficial to use a mask when entering the sea to check underwater and ensure that the turtle is not near the bottom. Moreover, swimmers should avoid going too far from the shore alone so that they can safely return in case the turtle appears. We assume that this turtle will eventually leave the area on its own. We invite you to send us your videos or photos so that we can learn more about this individual and the reasons for its presence in the Slatina area on Čiovo. According to eyewitness accounts, some individuals have interacted with the turtle despite the possibility of being bitten. We want to emphasize once again that this is a strictly protected animal, and such behavior is punishable by law.

Regarding the turtle incident at the beach in Petrčane, the police are conducting investigations, and upon completion, depending on the findings, charges will be filed against the individuals who mistreated this turtle. In case you witness such behaviour towards strictly protected species we are inviting you to call police or nature protection inspection through Service 112.

In both cases, it is evident that human activities, indirectly (Slatina) and directly (Petrčane), put these animals in danger while also exposing other people to risks and unpleasant incidents.

Dead loggerhead turtle entangled in marine debris.

We emphasize once again that sea turtles usually do not approach or interact with other larger animals or humans but keep a safe distance. It is extremely rare for sea turtles to bite humans, and such instances are isolated cases.

By nature, sea turtles are not aggressive animals, although males during the mating season may display signs of territoriality and dominance, using their strong bite.

Moreover, like most other animals, sudden proximity and contact with humans may startle and scare the animal, triggering its natural self-defense reaction.

Therefore, if you have the opportunity to observe a sea turtle in the sea, do not approach it, attempt to touch or disturb the animal. Sea turtles are wild animals not accustomed to close contact with humans, and due to their vulnerability and crucial role in the marine ecosystem, they are strictly protected.

As is the case for most marine organisms, the biggest threats to sea turtles are, in fact, a result of human activities. The main reasons for their endangerment today include interactions with fishing activities (where almost 10,000 loggerhead turtles in the Adriatic become accidental bycatch in fishing gear), collisions with vessels, pollution, and the destruction of their habitats. Since they are classified as endangered species, all three species of sea turtles that inhabit or appear in the Adriatic are strictly protected, and intentional disturbance, harassment, or hunting of these turtles is strictly prohibited.

Loggerhead turtle in Turtle rescue centre on Lošinj.

If you come across an injured, exhausted, or sick sea turtle, it is essential to contact the emergency services at 112 or directly reach out to the Sea Turtle Rescue Center in Lošinj at the phone number +385989981232 or email info@plavi-svijet.org.