When a marine turtle is incidentally by-caught by a longliner, fishermen try to cut the line -- without hauling it on board -- and release the turtle into the sea. However, a research published in the journal Marine Ecology Progress Series alerts that about 40% of post-released turtles die some months later due to the impact of longline fishing. The study is signed by experts Lluís Cardona and Irene Álvarez de Quevedo, from the Department of Animal Biology and the Biodiversity Research Institute of the University of Barcelona (IRBio), and Manu San Félix, from Vellmarí Formentera. It is the first scientific study based on satellite tracking of a group of loggerhead turtles released into the sea after being by-caught by Spanish longliners.
The Mediterranean Sea: a cul-de-sac
Loggerhead turtle (Caretta caretta) is the most common turtle inhabiting Mediterranean grounds and one of the most threatened species around the world. Its migrations are long; it comes back to sandy beaches to nest. Main nesting areas are located at North-American coast, Brazil, Japan, Oman, Australia, Cape Verde and Eastern Mediterranean (specially, Greece, Turkey, Cyprus and Libya). To be exact, in Spanish waters there are turtles of Atlantic and Eastern Mediterranean origin.
The Spanish longline fleet has been reported to by-catch around 10,000 turtles in the Mediterranean annually. However, more than 95% of them are still alive when longlines are collected. When looking for food, turtles bite baits and get caught by longliners' hooks. When a turtle is by-caught, fishers cut the line. Therefore, those turtles hooked in the jaw or the mouth and those hooked in the esophagus or the stomach are released into the sea.
It is not the hook, it is the line
Forty per cent of turtles released by fishermen die during the following three months. The problem is not the hook, it is the line. Professor Lluís Cardona, member of the Research Group on Large Marine Vertebrates of the UB, alerts: "The turtle shallows the line, and it goes down the alimentary tract until the end comes out through the cloaca."
"In the case of incidental by-catch -- points out the expert -- , turtles must be hauled on board, using a brail net, and line must be cut level with the hood. That will reduce incidental mortality by half and the impact on population will be acceptable," points out Cardona.
The Mediterranean is more dangerous for turtles of Atlantic origin More....