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Costa Rica is the country with most amount of turtles caught by longline fishing in the world

Longline fishing activities are responsable for this situation.

For every 1,000 hooks that are thrown into the sea, 14 turtles are snared

Costa Rica has the highest rate of sea turtles caught by longline fishing in the world. For every 1,000 hooks that are thrown into the sea, 14 turtles from different species are snared. This is higher than the global rate of two turtles for every 1,000 hooks.

“This information places Costa Rica as the country with the highest rate of turtles caught by longlining”, comments Randall Arauz, biologist and author of the study on the impact of Golden Dorada fishing on sea turtles and sharks.

This situation doesn´t occur on purpose. Sea turtles aren´t usually targets of fishing in the country but they can get snared on the hooks. This is known as “incidental fishing” (accidental).

Apart from Arauz, Sophie Whoriskey y Julia Baum from the University of Dalhousie, Canada, also sign the article that was published in the scientific magazine Biological Conservation.

To achieve their results, the investigators took observations onboard 12 ships of the Papagayo Seafood fleet in playa del Coco.
The observations took place between 1999 and 2008. In total 217 throws were counted, that is that the fishing line was thrown that amount of times.

Investigators registered all the catches, writing down if the animal was dead or alive and the use that was given to it afterwards, be it to return it to the sea, place it in a freezer o use it bait.

Dorado and longline. Accidental turtle fishing is related to dorado fishing.

Costa Rica is the fifth golden dorado fish exporter in the world, with 4,792 tons a year. Dorado is fished with longlining. This method consists in throwing a 25 kilometre long nylon line into the water, equipped with buoys so that it floats and, every ten metres, with a cord or string that carries the hook reaching down to between 15 and 20 metres.

The larger hauls for dorado are between october and february, with peaks between december and january.

During the time the study was carried out, 6,884 doradas were caught with 217 throws. “That is hardly 53 dorados per 1,000 hooks”, said Arauz.

Yearly, fishing for dorado can vary between three and 122 fishes per 1,000 hooks. “That proves that the dorado fish is very seasonal: When it´s the season, there are loads”, said the biologist.

Although they aren´t the objective, olive ridley sea turtles are the second most caught species by the longlining fleet. According to the study, 1,348 animals were caught by 217 throws. That would be nine turtles per 1,000 hooks.

The largest hauls take place between july and november, with peaks between september and october.

Also, there is an annual variation that is from 3 to 22 individuals per 1,000 hooks. “We have noticed that the olive ridley sea turtle is also very seasonal but their abundance doesn´t coincide with the dorado fish, which gives us options to protect them” said Arauz.

In contrast with the fish, the capture of olive ridley turtles grew throughout the years. In 1999 two turtles were caught for every 1,000 hooks but in 2008, 39 turtles were caught for every 1,000 hooks.

Also, the further the ship from the coast, less the number of turtles found on the longline.

“That has to do with the season and the landing beaches for this turtle, which are Nancite and Ostional. Logically, the closer to places where they nest on the coast, the more turtles you will find” explained Arauz.

Another observation that the scientists made was that the fishermen would leave the longline in the water for longer periods so as to catch more fish. This, more likely, increased the catches of olive ridley turtles: passing from 7 to 21 animals per every 1,000 hooks if the period was increased from 7 to 26 hours.

On the other hand, the death rate for turtles was relatively low. Of 100%, only 2% perished and this trend can be reversed. “That will depend on the fishermen and the considerations they will have when they take the hook off the turtle. It is proven that, with care and a circular type of hook that tends to only sticks to the mouth of the animal, the impact can be mitigated”, claimed Arauz.
Now, although the shark is not a target of their fishing, it is among the most caught species and is considered as complementary fishing.

The higher rates of hauls for grey sharks took place between july and november, with a peak between september and october.
As with the dorado fish, shark populations have decreased during the last few years. They went from 4,7 per 1,000 hooks in 1999 to less than 1 per each 1,000 hooks in 2008. With the study´s results, Arauz proposes to program fishing efforts throughout the year. Also, the expert believes that it is necessary to prepare national fishermen in turtle manipulating techniques so as to be able to remove the hooks from them and therefore reduce the mortality rate.

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