Endangered loggerhead sea turtle drowns in gillnet.

On Wednesday 25th, November, at 10:30 am, Peri Peri Divers were returning from a dive, when they spotted an adult male loggerhead turtle entangled in a gillnet. The boat was passing Praia de Rocha headland, ( approx. 8 km south of Tofo), an area popular with local artisanal fishers to set gillnets, where on this day, the divers counted ten nets set off the rocky headland. Gillnets are a wall of netting that hangs in the water column suspended from the surface by buoys. The nets are typically made of monofilament nylon and the mesh size is designed so that fish swim through and get caught by their gills as they try to reverse out of the net.
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Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

 

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Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

 

The skipper of Peri Peri Divers, noticed that one particular net seemed like it was being pulled down and suggested they check the net. After quick inspection of the net with mask and snorkels, it was noted that the net had a mobula ( also known as a devil ) ray entangled and already dead hanging about 5 m below the surface. The net appeared to have some thing larger entangled at the bottom but they could not clearly see, so they mounted their scuba gear and dove down to inspect the net properly. There, at the bottom they found a large sexually mature male loggerhead turtle (Caretta caretta) which is listed Endangered on the IUCN Red list in the Western Indian Ocean.
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Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

The divers acted quickly to try and untangle the turtle from the net but it was so badly tangled in the monofilament line (with a grid size of approx.  10 cm squared) that they used a knife to cut it out. Unfortunately the turtle was already dead on their arrival. It had swam into the net and got entangled so badly at the bottom of the net. Turtles, as marine reptiles need to be able to reach the surface to breathe air. Sadly, this turtle died of drowning whilst entangled in the net, stuck at 12 meters below the surface, unable to make it to the surface to breathe. Although the turtle was dead, the divers continued with their rescue mission, released the turtle and cautiously ascended to the surface escorting the turtle, incase there was an chance of survival for the animal. Despite their gallant rescue attempts, the turtle had seemingly drowned some time before their arrival so despite bringing the animal to the surface, it was past the point of resuscitating.
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Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

 

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Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

The loggerhead was brought ashore and the carcass was presented to local police so they could coordinate an official report with local maritime agency in Inhambane. At the police station, an official inspection of the animal was made by local sea turtle researcher, Jess Williams and measurements and genetic samples were collected. Male sea turtles, unless sick never return to land after they leave their home beach as baby turtles, so this portion of the population is scarcely studied and not well understood, so the samples collected from this animal will provide essential information to improve our understanding of the health and size of the population. It is estimated that loggerhead turtles of the SWIO reach sexual maturity around 36 years, so based on the size of this animal (92 cm carapace length, 84 cm width) we can assume that it was at least 36 years old. Being a mature, male loggerhead turtles, it is highly likely that it recently migrated into the Praia do Tofo/ Inhambane coast line for the mating and nesting season. Photos of the scale pattern on the left and right sides of the turtles face were also collected and compared with the photo identification database which has been running in Tofo now for over five years. However no match was found suggesting that this animal was new to the area.

Left profile

Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

Male turtles will mate with as many many females as possible and mating pairs of turtles can often be seen coupled at the surface. The nesting season runs from November to March each year here in Southern Mozambique, which means there are likely to be a lot turtles sighted in the water and on the nesting beaches over the next few months.  Both mature male and female turtles migrate long distances (some times several thousand km) to return to use the coastal habitat here for mating and then the female turtles return to their natal or home beaches, where they were born some 36 or more years ago to lay multiple clutches of eggs throughout the nesting season.
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Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

The use of gillnets in coastal waters has become increasingly popular in recent years by local fishers. It is a favourable approach with local fishers because it often entangles anything it swims into which maximises the success of their catch. Unfortunately, this kind of fishing method, because of its lack of target species, is not a sustainable method and is known to have very high rates of by-catch often including charismatic mega fauna species like sea turtles, dolphins, dugongs, sharks and rays.  This fishing approach can have even more devastating effects when nets are set in migratory corridors of such mega fauna species. The nearshore waters adjacent to the Praia de Rocha headland are thought to be utilised by whale sharks, two species of manta ray, two species of dolphin, 4 species of sea turtle and many species of sharks as a movement corridor. Whilst by-catch of mega fauna species occurs year round, the rate of catching turtles is likely to be higher during the nesting season as there are more animals in the area. All sea turtles are protected by Mozambican law and targeting hunting for turtles can result in jail time or large fines if caught. The catch of turtles in such nets has a particularly devastating impact on the population as it removes many of the sexually mature males and females who have returned to the area to breed and these animals are likely to be very old (> 36 yrs).
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Loggerhead turtle, found dead entangled in a gillnet at Praia de Rocha, Inhambane Province (Photo credit: Alexandra Patane and Ole Siegfried).

Footage of the rescue effort was kindly supplied by Alexandra Patane and Ole Siegfried. Many thanks to all the divers who were involved with the attempted rescue and recovery of the turtle (Especially, K. Reeve-Arnold, R. Newbigging and J. Cross) and Peri Peri Divers for bringing the large heavy turtle ashore with their boat.
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