12 dead loggerhead turtles found – which are the biggest threats to sea turtles

glavata želva

In Sakarun Bay on Dugi otok last week, the sea washed ashore the bodies of 12 dead loggerhead sea turtles (Caretta caretta). According to the first findings of the autopsy, carried out at the Croatian Veterinary Institute in Zagreb, some of the turtles were found to have pathological changes that indicate drowning, while others were found to have changes that suggest sepsis. Interestingly, a large number of individuals were found, considering that loggerhead turtles do not usually move in groups. Further autopsy and organ analysis will provide additional information.

Let’s meet the loggerhead turtle

It is estimated that about twenty thousand loggerhead turtles live in the Adriatic Sea. The weight of the dead individuals in the Sakarun Bay was on average about fifty kilograms, so it is assumed that they are individuals of a younger population, which are not yet ready to breed.

Sea turtles, like freshwater turtles, hibernate during the colder months. During that period, they become lethargic and lay on the seabed, covered with mud, and often partially buried in the sediment. They periodically surface for 5 to 7 minutes to breathe air, after which they return to the bottom. The duration of their dive varies depending on the time of year. Research conducted in 2005 showed that the length of the dive increased from 5.5 minutes in July to 341 minutes in February.

Turtles are known to be excellent swimmers and can move in the opposite direction of sea currents, while surface circulation can facilitate their dispersal. Although Sakarun Bay faces south, the chances that they were washed ashore just because of a strong southerly wind, according to the experts, are very small.

glavata želva
Glavata želva, autor: Goran Šafarek

What threatens loggerhead turtles?

Although it is a fishing ban season, the Croatian Veterinary Institute does not rule out the possibility that the death occurred due to interaction with fishing gear. A trawl can lift turtles from the seabed to the surface. With a sudden emergence, the half-awake turtles are disoriented and can hit the shore. Likewise, turtles that come across a vessel in such a state are very slowed down and give the impression that they have died. Their sudden return to the sea can lead to drowning.

The situation is similar with set nets – the problem arises when turtles get entangled and the net suffocates them. On the other hand, when encountering fishing gear such as hooks and lines, they may swallow the baited hook which thus causes, internal bleeding.

Thus, bycatch on fishing gear represents one of the biggest problems affecting the population of sea turtles. Reducing bycatch, increasing surveillance at sea, and preventing illegal fishing should be the goals of modern sustainable fisheries.

The second most common cause of turtle mortality is collisions with boats. Collisions with boats can cause fractures or cuts to the shell, head, or limbs. Mortality is also common when swallowing marine litter, especially plastic, which due to its appearance turtles can mistake for food.

It is true that, apart from man and climate change, in the adult phase in the Adriatic Sea, turtles have no enemies. However, it is estimated that more than 5,000,000 sea turtles are caught by trawlers in the Adriatic Sea every year. According to the available literature, the bycatch of turtles in the Mediterranean Sea is around 132,000 individuals per year, with a high number of deaths, over 44,000 per year.

The International Union for Conservation of Nature (IUCN) recognized sea turtles as one of the most endangered groups in the world and included them on the Red List and under strict protection in all European Union countries.

By Kristin Snippe, Unsplash

What can we do for sea turtles?

During sailing or fishing activities, there is a possibility of spotting, as well as accidentally catching, sea turtles. Below we suggest what we can all do to protect sea turtles and reduce their mortality.

  • If you see sea turtles while sailing, keep a minimum distance of 45.7 m (50 y). Do not disturb them.
  • If sea turtles are accidentally caught with fishing gear, the turtles must be kept on deck for some time. They should be in a position where their back is slightly higher than their head to facilitate the expulsion of water from their lungs. Once they are active again, you can release them back into the sea. Report this bycatch of a sensitive species through a logbook or catch report.
  • If you find dead, sick, or injured strictly protected marine animals, including turtles, mammals, and cartilaginous fish, report it to 112. In Croatia, a Protokol (in Croatian only) has been established for action in these situations.

There are also various solutions to mitigate the bycatch of sea turtles during the fishing activities. These are changes in fishing techniques and/or modifications of fishing gear:

  • reducing the time of soaking the nets in the sea
  • use of circular hooks instead of traditional J-shaped hooks (circular hooks are wider and less likely to be swallowed by turtles)
  • use of TED devices (Turtle Excluder Device) that enable the escape of sea turtles from trawl nets.

In conclusion, importance should be attached to the adequate protection of sandy beaches, which are the main breeding grounds for sea turtles, as well as to the implementation of better surveillance at sea, and thus to the prevention of illegal fishing. The establishment of a recovery centre for sea turtles is also one of the effective solutions to this problem. It is also very important to reduce the generation of plastic waste and to better regulate waste disposal sites to reduce the intake of waste into the sea.

https://www.fao.org/3/i8951en/I8951EN.pdf

Unexpected meeting of a Croatian fisherman with a sea turtle – an example of good practice

Although this is an extremely sad event, which led to a drastic reduction in the population of loggerhead turtles in the Adriatic Sea, it is still an opportunity to learn something and point to positive examples. Thus, in a flurry of different media announcements, the one showing the proper fishermen’s treatment of a bycatch turtle came out.

The fisherman took the sleepy individual out to the vessel, adjusted it in the correct position, and waited for it to come to its senses. After two hours, the animal fully recovered and was returned to the sea. He even removed the barnacles that covered her eyes and nose. Of course, the bycatch was reported through the logbook.

Kudos to the fisherman! Protecting the sea and its inhabitants today is an investment in a better tomorrow. We hope that such examples of good practice will become more frequent in the future!

Used literature:

  • Gvozdenović Nikolić, Slađana & Vuk, Iković. (2015). Dead sea turtles on the Montenegrin coast. Studia Marina. 28. 61-66.
  • Casale, Paolo & Freggi, Daniela & Basso, Roberto & Argano, Roberto. (2005). Interaction of the Static Net Fishery with Loggerhead Sea Turtles in the Mediterranean: Insights from Mark-recapture Data. The Herpetological Journal. 15. 201-203.
  • Hochscheid, Sandra & Bentivegna, Flegra & Hays, Graeme. (2005). First records of dive durations for a hibernating sea turtle. Biology letters. 1. 82-6. 10.1098/rsbl.2004.0250.
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